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Re: [PATCH v2 00/15] accel/qda: Qualcomm DSP Accelerator driver

by Krzysztof Kozlowski

On 19/08/2026 16:49, Rob Clark wrote: > On Wed, Aug 19, 2026 at 7:43 AM Krzysztof Kozlowski <krzk(a)kernel.org> wrote: >> >> On 19/08/2026 16:38, Rob Clark wrote: >>> On Wed, Aug 19, 2026 at 7:21 AM Krzysztof Kozlowski <krzk(a)kernel.org> wrote: >>>> >>>> On 19/08/2026 15:26, Ekansh Gupta wrote: >>>>> On 19-08-2026 00:43, Krzysztof Kozlowski wrote: >>>>>> On 17/08/2026 06:47, Ekansh Gupta wrote: >>>>>>> This patch series introduces the Qualcomm DSP Accelerator (QDA) driver, >>>>>>> a DRM-based accelerator driver for Qualcomm DSPs. The driver provides a >>>>>>> standardized interface for offloading computational tasks to DSPs found >>>>>>> on Qualcomm SoCs, supporting all DSP domains. >>>>>>> >>>>>>> The QDA driver implements the FastRPC protocol over the DRM accel >>>>>>> subsystem. It uses the same device-tree node structure as the existing >>>>>>> fastrpc driver in drivers/misc/. The approach for binding the QDA driver >>>>>>> to device-tree nodes while coexisting with the fastrpc driver is an open >>>>>>> item described below. >>>>>> >>>>>> No. Grow/replace/improve existing driver instead of coming with a duplicate. >>>>>> >>>>>> That's a standard upstream requirement, basically given on every >>>>>> upstreaming guide. >>>>>> >>>>>> Please watch old talk from Greg - "I Don’t Want Your Code!". >>>>> Posted discussion threads here[1]. Would seek comments from Dmitry, >>>>> Srini as well. >>>>> >>>>> [1] >>>>> https://lore.kernel.org/all/3476b5c3-7983-4994-a901-3d7d8bd75255@oss.qualco… >>>> >>>> The rest of the comments is still valid even if you did not acknowledge >>>> them. >>>> >>>> Anyway, regarding above - again, watch the talk from Greg. >>>> >>>> You have ONE driver. Not two. >>> >>> Long term, moving to the common driver framework (which did not exist >>> when fastrpc was first created) seems like a good thing. But does >>> that not allow for some transition period? How can we get from here >>> to there without otherwise breaking userspace? Is there some other >>> precedent elsewhere in other driver subsystems? >> >> Yes, Iris and Venus where we agreed for an exception (two drivers) as >> long as new driver supports old hardware / features. >> >> This is not the case here, right? >> >>> >>> I suppose drm exposing legacy fbdev on top of drm drivers is _sort of_ >>> a precedent if you squint a bit? I'm not really familiar enough to >>> say if that would be reasonable/possible in this case. >> >> Growing old driver does not look complicated itself. The only a bit >> tricky thing is to present somehow exclusive interface to user-space, >> like usage of one disables the second etc. Depending on actual >> differences in that interface. >> >> But having a duplicated driver is a clear no go and it is well known >> upstream requirement. Nothing new here. > > Would it be acceptable as a first step to, by default (ie. when no > cmdline override/etc) for the new driver to bind to new compatibles You have one compatible. > and the existing driver to old? Ie. have both drivers but only one > binds on a given platform? I don't see how is it possible to write such DTS, because - repeating my question - how many hardware blocks is there? I believe only one per given DSP, so how could you have two device nodes? Best regards, Krzysztof

1 month

Re: [PATCH v2 00/15] accel/qda: Qualcomm DSP Accelerator driver

by Krzysztof Kozlowski

On 19/08/2026 16:38, Rob Clark wrote: > On Wed, Aug 19, 2026 at 7:21 AM Krzysztof Kozlowski <krzk(a)kernel.org> wrote: >> >> On 19/08/2026 15:26, Ekansh Gupta wrote: >>> On 19-08-2026 00:43, Krzysztof Kozlowski wrote: >>>> On 17/08/2026 06:47, Ekansh Gupta wrote: >>>>> This patch series introduces the Qualcomm DSP Accelerator (QDA) driver, >>>>> a DRM-based accelerator driver for Qualcomm DSPs. The driver provides a >>>>> standardized interface for offloading computational tasks to DSPs found >>>>> on Qualcomm SoCs, supporting all DSP domains. >>>>> >>>>> The QDA driver implements the FastRPC protocol over the DRM accel >>>>> subsystem. It uses the same device-tree node structure as the existing >>>>> fastrpc driver in drivers/misc/. The approach for binding the QDA driver >>>>> to device-tree nodes while coexisting with the fastrpc driver is an open >>>>> item described below. >>>> >>>> No. Grow/replace/improve existing driver instead of coming with a duplicate. >>>> >>>> That's a standard upstream requirement, basically given on every >>>> upstreaming guide. >>>> >>>> Please watch old talk from Greg - "I Don’t Want Your Code!". >>> Posted discussion threads here[1]. Would seek comments from Dmitry, >>> Srini as well. >>> >>> [1] >>> https://lore.kernel.org/all/3476b5c3-7983-4994-a901-3d7d8bd75255@oss.qualco… >> >> The rest of the comments is still valid even if you did not acknowledge >> them. >> >> Anyway, regarding above - again, watch the talk from Greg. >> >> You have ONE driver. Not two. > > Long term, moving to the common driver framework (which did not exist > when fastrpc was first created) seems like a good thing. But does > that not allow for some transition period? How can we get from here > to there without otherwise breaking userspace? Is there some other > precedent elsewhere in other driver subsystems? Yes, Iris and Venus where we agreed for an exception (two drivers) as long as new driver supports old hardware / features. This is not the case here, right? > > I suppose drm exposing legacy fbdev on top of drm drivers is _sort of_ > a precedent if you squint a bit? I'm not really familiar enough to > say if that would be reasonable/possible in this case. Growing old driver does not look complicated itself. The only a bit tricky thing is to present somehow exclusive interface to user-space, like usage of one disables the second etc. Depending on actual differences in that interface. But having a duplicated driver is a clear no go and it is well known upstream requirement. Nothing new here. Best regards, Krzysztof

1 month

Re: [PATCH v2 00/15] accel/qda: Qualcomm DSP Accelerator driver

by Krzysztof Kozlowski

On 19/08/2026 15:26, Ekansh Gupta wrote: > On 19-08-2026 00:43, Krzysztof Kozlowski wrote: >> On 17/08/2026 06:47, Ekansh Gupta wrote: >>> This patch series introduces the Qualcomm DSP Accelerator (QDA) driver, >>> a DRM-based accelerator driver for Qualcomm DSPs. The driver provides a >>> standardized interface for offloading computational tasks to DSPs found >>> on Qualcomm SoCs, supporting all DSP domains. >>> >>> The QDA driver implements the FastRPC protocol over the DRM accel >>> subsystem. It uses the same device-tree node structure as the existing >>> fastrpc driver in drivers/misc/. The approach for binding the QDA driver >>> to device-tree nodes while coexisting with the fastrpc driver is an open >>> item described below. >> >> No. Grow/replace/improve existing driver instead of coming with a duplicate. >> >> That's a standard upstream requirement, basically given on every >> upstreaming guide. >> >> Please watch old talk from Greg - "I Don’t Want Your Code!". > Posted discussion threads here[1]. Would seek comments from Dmitry, > Srini as well. > > [1] > https://lore.kernel.org/all/3476b5c3-7983-4994-a901-3d7d8bd75255@oss.qualco… The rest of the comments is still valid even if you did not acknowledge them. Anyway, regarding above - again, watch the talk from Greg. You have ONE driver. Not two. Best regards, Krzysztof

1 month

Re: [PATCH v2 00/15] accel/qda: Qualcomm DSP Accelerator driver

by Krzysztof Kozlowski

On 19/08/2026 15:32, Ekansh Gupta wrote: > On 19-08-2026 00:51, Krzysztof Kozlowski wrote: >> On 18/08/2026 21:13, Krzysztof Kozlowski wrote: >>> On 17/08/2026 06:47, Ekansh Gupta wrote: >>>> This patch series introduces the Qualcomm DSP Accelerator (QDA) driver, >>>> a DRM-based accelerator driver for Qualcomm DSPs. The driver provides a >>>> standardized interface for offloading computational tasks to DSPs found >>>> on Qualcomm SoCs, supporting all DSP domains. >>>> >>>> The QDA driver implements the FastRPC protocol over the DRM accel >>>> subsystem. It uses the same device-tree node structure as the existing >>>> fastrpc driver in drivers/misc/. The approach for binding the QDA driver >>>> to device-tree nodes while coexisting with the fastrpc driver is an open >>>> item described below. >>> >>> No. Grow/replace/improve existing driver instead of coming with a duplicate. >>> >>> That's a standard upstream requirement, basically given on every >>> upstreaming guide. >>> >>> Please watch old talk from Greg - "I Don’t Want Your Code!". >>> >>>> >>>> v1: https://lore.kernel.org/all/20260519-qda-series-v1-0-b2d984c297f8@oss.qualc… >>>> RFC: https://lore.kernel.org/dri-devel/20260224-qda-firstpost-v1-0-fe46a9c1a046@… >>>> >>>> Changes since v1 >>>> ================ >>>> >>>> The v1 review raised two architectural objections and one correctness >>>> issue; all three are resolved in v2: >>>> >>>> * Christian König (dma-buf maintainer) pointed out that the imported- >>>> buffer path silently assumed the IOMMU maps every buffer as a single >>>> contiguous range, which is not guaranteed. v2 walks the scatterlist >>>> and cleanly rejects non-contiguous imports; contiguous imports (e.g. >>>> CMA DMA-buf heap) are accepted. (patch 11) >>>> >>>> * Dmitry Baryshkov objected to three different buffer-passing formats >>>> in the invoke IOCTL (DMA-BUF fd, direct/inline, DMA handle). v2 >>>> passes only GEM handles; userspace imports any fd to a GEM handle >>>> with DRM_IOCTL_PRIME_FD_TO_HANDLE before invoking. Packing and >>>> overlap handling are left to userspace. (patch 12) >>>> >>>> * The memory manager (patch 07) used a fixed 16-entry array without >>>> justification and leaked the device descriptor on teardown. v2 >>>> allocates the array from the DT context-bank count (as Dmitry >>>> suggested) and frees it correctly. >>>> >>>> User-space staging branch >>>> ========================= >>>> https://github.com/qualcomm/fastrpc/tree/accel/staging >>>> >>>> Key Features >>>> ============ >>>> >>>> * Standard DRM accelerator interface via /dev/accel/accelN >>>> * GEM-based buffer management with DMA-BUF import (PRIME) >>>> * IOMMU-based memory isolation using per-process context banks >>>> * FastRPC protocol implementation for DSP communication >>>> * RPMsg transport layer for reliable message passing >>>> * Support for all DSP domains (ADSP, CDSP, SDSP, GDSP) >>>> * DRM IOCTL interface for DSP session management, buffer allocation, >>>> and remote procedure invocation >>>> >>>> Architecture >>>> ============ >>>> >>>> 1. DRM Accelerator Framework Integration >>>> The driver registers as a DRM accel device, exposing a standard >>>> /dev/accel/accelN character device node. This provides established >>>> DRM infrastructure for device management, file operations, and >>>> IOCTL dispatch. >>>> >>>> 2. Memory Management >>>> Buffers are managed as GEM objects with PRIME support for DMA-BUF >>>> import. This enables buffer sharing with other DRM drivers (GPU, >>>> camera, video) using standard kernel mechanisms. Only contiguous >>>> imports are accepted; the driver verifies contiguity at import time >>>> rather than assuming it. >>>> >>>> 3. IOMMU Context Bank Management >>>> IOMMU context banks (CBs) are represented as proper struct device >>>> instances on a custom virtual bus (qda-compute-cb). Each CB device >>>> is registered with the IOMMU subsystem and receives its own IOMMU >>>> domain, enabling per-session address space isolation. The custom >>>> bus was introduced because IOMMU context banks are synthetic >>>> constructs — not real platform devices — and to ensure CB device >>>> lifetime is strictly subordinate to the parent QDA device. >>>> See also: https://lore.kernel.org/all/245d602f-3037-4ae3-9af9-d98f37258aae@oss.qualco… >>>> >>>> 4. Memory Manager Architecture >>>> The memory manager maintains a registry of IOMMU devices in an >>>> array sized to the number of context banks described in the device >>>> tree, and coordinates per-process device assignment with reference- >>>> counted lifetime management. The DMA-coherent backend allocates >>>> buffers with SID-prefixed DMA addresses for DSP firmware >>>> compatibility. >>>> >>>> 5. Transport Layer >>>> RPMsg communication is handled in a dedicated transport layer >>>> (qda_rpmsg.c), separate from the core DRM driver logic. >>>> >>>> 6. Code Organization >>>> The driver is organized across multiple files (~4800 lines total): >>>> * qda_drv.c: Core driver and DRM integration >>>> * qda_rpmsg.c: RPMsg transport layer >>>> * qda_cb.c: Context bank device management >>>> * qda_compute_bus.c: Custom virtual bus for CB devices >>>> * qda_gem.c: GEM object management >>>> * qda_prime.c: DMA-BUF import (PRIME) >>>> * qda_memory_manager.c: IOMMU device registry and allocation >>>> * qda_memory_dma.c: DMA-coherent allocation backend >>>> * qda_fastrpc.c: FastRPC protocol implementation >>>> * qda_ioctl.c: IOCTL dispatch >>>> >>>> 7. UAPI Design >>>> The driver exposes DRM-style IOCTLs defined in >>>> include/uapi/drm/qda_accel.h, following DRM UAPI conventions >>>> (__u32/__u64 types, C++ guard, GPL-2.0-only WITH Linux-syscall-note). >>>> Buffer arguments are identified by GEM handles; the driver never >>>> accepts DMA-BUF fds directly in any IOCTL. >>>> >>>> Patch Series Organization >>>> ========================== >>>> >>>> Patch 01: MAINTAINERS entry >>>> Patch 02: Driver documentation (Documentation/accel/qda/) >>>> Patches 03-04: Core driver skeleton and compute bus >>>> Patch 05: iommu: Register qda-compute-cb bus with IOMMU subsystem >>>> Patches 06-07: CB device enumeration and memory manager >>>> Patch 08: QUERY IOCTL and UAPI header >>>> Patches 09-11: GEM buffer management and PRIME import >>>> Patches 12-15: FastRPC protocol (invoke, session create/release, >>>> map/unmap) >>>> >>>> Open Items >>>> =========== >>>> >>>> 1. Device-Tree Compatible String >>>> The QDA driver uses the same device-tree node structure and >>>> properties as the existing fastrpc driver in drivers/misc/. A >>>> mechanism is needed to allow the QDA driver to bind to its device >>>> node independently of the fastrpc driver. >>>> >>>> The intended coexistence model is: platforms that require the >>>> complete fastrpc feature set continue to use "qcom,fastrpc"; new >>>> platforms where QDA's feature set is sufficient use a QDA-specific >>>> compatible string. New feature development is directed toward QDA. >>>> >>>> The options under consideration are: >>>> >>>> a) Add a new "qcom,qda" compatible string to the existing >>>> qcom,fastrpc.yaml binding, since the DT node structure and >>>> properties are identical. >>> No >>> >>>> >>>> b) Introduce a separate qcom,qda.yaml binding that references or >>>> inherits the fastrpc binding properties. >>> >>> No >>> >>>> >>>> Seeking guidance from DT binding maintainers on the preferred >>>> approach. >>> >>> Grow existing driver. You do not get new driver, you do not get new >>> bindings. >>> >> >> And this was already questioned at v1 (the true v1, not v1+1) but you >> ignored the comment. > The discussion were around compat layers in v1 patch (which is not yet > concluded) and on whether this driver is going to be an alternative or a No, you got comment, from Trilok I think, asking what is the plan in respect of existing fastrpc driver. Best regards, Krzysztof

1 month

Re: [PATCH v2 03/15] accel/qda: Add initial QDA DRM accelerator driver

by Krzysztof Kozlowski

On 19/08/2026 15:17, Ekansh Gupta wrote: > On 19-08-2026 00:40, Krzysztof Kozlowski wrote: >> On 17/08/2026 06:47, Ekansh Gupta wrote: >>> Add the skeleton of the Qualcomm DSP Accelerator (QDA) driver, a DRM >>> accel driver for the Hexagon DSPs found on Qualcomm SoCs. >>> >>> This patch registers a DRM accel device, exposing a /dev/accel/accelN >>> character device node, and binds it to the RPMsg channel used to reach >>> the DSP. Buffer management, IOMMU context banks and the FastRPC >>> protocol are added by later patches in this series. >>> >>> qda_drv.c / qda_drv.h define the drm_driver ops table, the per-file >>> private state (qda_file_priv) and the main device structure (qda_dev), >>> which embeds drm_device so that it can be recovered with container_of(). >>> >>> qda_rpmsg.c binds to the "qcom,fastrpc" compatible via >>> module_rpmsg_driver(), reads the DSP domain name from the "label" >>> device-tree property, and registers the DRM device. >>> >>> Assisted-by: Claude:claude-sonnet-5 >>> Signed-off-by: Ekansh Gupta <ekansh.gupta(a)oss.qualcomm.com> >>> --- >>> Changes in v2: >>> - Use module_rpmsg_driver() and drop the qda_rpmsg_register()/ >>> _unregister() wrappers, module_init()/module_exit() and >>> qda_rpmsg.h entirely (Dmitry Baryshkov) >>> - Read the "label" property directly into qdev->dsp_name (Dmitry Baryshkov) >>> - Drop the probe/remove/init log messages (Dmitry Baryshkov) >>> - Return the result of qda_register_device() directly (Dmitry Baryshkov) >>> - Clarify the Kconfig help text (Dmitry Baryshkov) >>> --- >>> drivers/accel/Kconfig | 1 + >>> drivers/accel/Makefile | 1 + >>> drivers/accel/qda/Kconfig | 30 ++++++++++++++++ >>> drivers/accel/qda/Makefile | 10 ++++++ >>> drivers/accel/qda/qda_drv.c | 71 ++++++++++++++++++++++++++++++++++++++ >>> drivers/accel/qda/qda_drv.h | 61 +++++++++++++++++++++++++++++++++ >>> drivers/accel/qda/qda_rpmsg.c | 79 +++++++++++++++++++++++++++++++++++++++++++ >>> 7 files changed, 253 insertions(+) >>> >>> diff --git a/drivers/accel/Kconfig b/drivers/accel/Kconfig >>> index bdf48ccafcf2..74ac0f71bc9d 100644 >>> --- a/drivers/accel/Kconfig >>> +++ b/drivers/accel/Kconfig >>> @@ -29,6 +29,7 @@ source "drivers/accel/ethosu/Kconfig" >>> source "drivers/accel/habanalabs/Kconfig" >>> source "drivers/accel/ivpu/Kconfig" >>> source "drivers/accel/qaic/Kconfig" >>> +source "drivers/accel/qda/Kconfig" >>> source "drivers/accel/rocket/Kconfig" >>> >>> endif >>> diff --git a/drivers/accel/Makefile b/drivers/accel/Makefile >>> index 1d3a7251b950..58c08dd5f389 100644 >>> --- a/drivers/accel/Makefile >>> +++ b/drivers/accel/Makefile >>> @@ -5,4 +5,5 @@ obj-$(CONFIG_DRM_ACCEL_ARM_ETHOSU) += ethosu/ >>> obj-$(CONFIG_DRM_ACCEL_HABANALABS) += habanalabs/ >>> obj-$(CONFIG_DRM_ACCEL_IVPU) += ivpu/ >>> obj-$(CONFIG_DRM_ACCEL_QAIC) += qaic/ >>> +obj-$(CONFIG_DRM_ACCEL_QDA) += qda/ >>> obj-$(CONFIG_DRM_ACCEL_ROCKET) += rocket/ >>> \ No newline at end of file >> >> You have trivial patch errors. > newline problem was already there, wasn't introduced as part of this > patch series, so I wasn't sure to fix it here. I can fix this in v3.> >> ... >> >>> +} >>> + >>> +static const struct of_device_id qda_rpmsg_id_table[] = { >>> + { .compatible = "qcom,fastrpc" }, >>> + {}, >> >> Device node with this compatible is already populated, so this looks >> simply wrong or you are adding a duplicated driver. >> >> That's a no-go, you are supposed to work with existing drivers and grow >> them. > I'll bring the discussion again here, there was a discussion to move the > driver to accel subsystem if we want to support new features/uAPI > changes. Please read [1],[2] threads. The intention is to replace > fastrpc driver with QDA eventually. None of them address the problem. You want to grow fastrpc into user of dmabuf? So you move it from misc to here. Again: you have one driver. > > Do you suggest adding a different compatible, say "qcom,qda" for this > driver? How would that even work? How much (or many?) hardware do you have in your SoC? > > Let me know if you have a better suggestion to proceed here. > > [1] https://lkml.org/lkml/2024/6/24/479 > [2] https://lkml.org/lkml/2024/6/21/1252> Please do not ever reference lkml.org, it's long time deprecated and barely working. Use lore. Best regards, Krzysztof

1 month

Re: [PATCH v2 01/15] MAINTAINERS: Add entry for Qualcomm DSP Accelerator (QDA) driver

by Krzysztof Kozlowski

On 19/08/2026 15:05, Ekansh Gupta wrote: > On 19-08-2026 00:52, Krzysztof Kozlowski wrote: >> On 17/08/2026 06:47, Ekansh Gupta wrote: >>> Add a MAINTAINERS entry for the Qualcomm DSP Accelerator (QDA) driver, >>> covering the driver source under drivers/accel/qda, documentation under >>> Documentation/accel/qda, and the UAPI header >>> include/uapi/drm/qda_accel.h. The linux-arm-msm and dri-devel mailing >>> lists are listed as the relevant review lists. >>> >>> Signed-off-by: Ekansh Gupta <ekansh.gupta(a)oss.qualcomm.com> >>> --- >>> MAINTAINERS | 11 +++++++++++ >>> 1 file changed, 11 insertions(+) >>> >>> diff --git a/MAINTAINERS b/MAINTAINERS >>> index 912837dd4640..75fa90c137c7 100644 >>> --- a/MAINTAINERS >>> +++ b/MAINTAINERS >>> @@ -22388,6 +22388,17 @@ S: Supported >>> F: Documentation/devicetree/bindings/crypto/qcom-qce.yaml >>> F: drivers/crypto/qce/ >>> >>> +QUALCOMM DSP ACCELERATOR (QDA) DRIVER >>> +M: Ekansh Gupta <ekansh.gupta(a)oss.qualcomm.com> >>> +L: linux-arm-msm(a)vger.kernel.org >>> +L: dri-devel(a)lists.freedesktop.org >>> +S: Supported >>> +T: git https://gitlab.freedesktop.org/drm/misc/kernel.git >>> +F: Documentation/accel/qda/ >> >> There is no such directory. > the directory got added in a later patch, added this patch at the start > following the comment here[1]. > This comment did not tell you to make it non-bisectable. This comment asked you to add that parts in your first patch. Why did you move patches instead of adding this into the first one? Best regards, Krzysztof

1 month

Re: [PATCH 1/9] dma-buf: add dma_fence_was_initialized function v2

by Philipp Stanner

On Wed, 2026-08-19 at 10:59 +0200, Jiri Slaby wrote: > On 14. 07. 26, 10:43, Philipp Stanner wrote: > > On Tue, 2026-07-14 at 09:53 +0200, Philipp Stanner wrote: > > > On Mon, 2026-07-13 at 10:58 +0200, Jiri Slaby wrote: > > > > Hi, > > > > > > > > On 20. 01. 26, 11:54, Christian König wrote: > > > > > Some driver use fence->ops to test if a fence was initialized or not. > > > > > The problem is that this utilizes internal behavior of the dma_fence > > > > > implementation. > > > > > > > > > > So better abstract that into a function. > > > > > > > > > > v2: use a flag instead of testing fence->ops, rename the function, move > > > > > to the beginning of the patch set. > > > > ... > > > > > --- a/drivers/gpu/drm/qxl/qxl_release.c > > > > > +++ b/drivers/gpu/drm/qxl/qxl_release.c > > > > > @@ -146,7 +146,7 @@ qxl_release_free(struct qxl_device *qdev, > > > > > idr_remove(&qdev->release_idr, release->id); > > > > > spin_unlock(&qdev->release_idr_lock); > > > > > > > > > > - if (release->base.ops) { > > > > > + if (dma_fence_was_initialized(&release->base)) { > > > > > > Could you verify the cause with sth like > > > > > > if (release->base.ops && dma_fence_was_initialized(…)) { > > > > Forget about that, probably would not work or cause other issues > > because the NULL-setting on signal(). > > > > I'd then probably try to verify it with a separate boolean in struct > > release. Though I also don't get why the fence-initialized check does > > not do the trick. > > Hi, have you come up with something yet? Well, I was more like suggesting this as a debug option [to you] :D Regardless, looking at the code again, I would say that this might be a race, but I don't know enough about QXL to say for sure. dma_fence_init() is (of course) not ordered: static void __dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, spinlock_t *lock, u64 context, u64 seqno, unsigned long flags) { BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name); kref_init(&fence->refcount); /* * While it is counter intuitive to protect a constant function pointer * table by RCU it allows modules to wait for an RCU grace period * before they unload, to make sure that nobody is executing their * functions any more. */ RCU_INIT_POINTER(fence->ops, ops); INIT_LIST_HEAD(&fence->cb_list); fence->context = context; fence->seqno = seqno; fence->flags = flags | BIT(DMA_FENCE_FLAG_INITIALIZED_BIT); (Should this maybe be set_bit() btw?) The fact that QXL could run into qxl_release_free() with an uninitialized fence hints at the fact that this might race, so DMA_FENCE_FLAG_INITIALIZED_BIT could be set / read before kref_init() ran. Maybe one way to verify / debug that would be to move spin_unlock(&qdev->release_idr_lock) downwards so it also guards dma_fence_was_initialized(), and also lock the initialization of the fence (in qxl_release_fence_buffer_objects() ?) with said lock. If that's possible. Just brainstorming a bit for ways how to debug. QXL does a few tricky things with the release->base.ops pointer. qxl_release_alloc() sets it to NULL, and only qxl_release_fence_buffer_objects() then actually sets it. So this could be the race? Setting of the ops pointer got replaced by setting of the fence-flag. P.

1 month

Re: [PATCH v2 01/15] MAINTAINERS: Add entry for Qualcomm DSP Accelerator (QDA) driver

by Krzysztof Kozlowski

On 17/08/2026 06:47, Ekansh Gupta wrote: > Add a MAINTAINERS entry for the Qualcomm DSP Accelerator (QDA) driver, > covering the driver source under drivers/accel/qda, documentation under > Documentation/accel/qda, and the UAPI header > include/uapi/drm/qda_accel.h. The linux-arm-msm and dri-devel mailing > lists are listed as the relevant review lists. > > Signed-off-by: Ekansh Gupta <ekansh.gupta(a)oss.qualcomm.com> > --- > MAINTAINERS | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/MAINTAINERS b/MAINTAINERS > index 912837dd4640..75fa90c137c7 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -22388,6 +22388,17 @@ S: Supported > F: Documentation/devicetree/bindings/crypto/qcom-qce.yaml > F: drivers/crypto/qce/ > > +QUALCOMM DSP ACCELERATOR (QDA) DRIVER > +M: Ekansh Gupta <ekansh.gupta(a)oss.qualcomm.com> > +L: linux-arm-msm(a)vger.kernel.org > +L: dri-devel(a)lists.freedesktop.org > +S: Supported > +T: git https://gitlab.freedesktop.org/drm/misc/kernel.git > +F: Documentation/accel/qda/ There is no such directory. Best regards, Krzysztof

1 month

Re: [PATCH v2 00/15] accel/qda: Qualcomm DSP Accelerator driver

by Krzysztof Kozlowski

On 17/08/2026 06:47, Ekansh Gupta wrote: > This patch series introduces the Qualcomm DSP Accelerator (QDA) driver, > a DRM-based accelerator driver for Qualcomm DSPs. The driver provides a > standardized interface for offloading computational tasks to DSPs found > on Qualcomm SoCs, supporting all DSP domains. > > The QDA driver implements the FastRPC protocol over the DRM accel > subsystem. It uses the same device-tree node structure as the existing > fastrpc driver in drivers/misc/. The approach for binding the QDA driver > to device-tree nodes while coexisting with the fastrpc driver is an open > item described below. No. Grow/replace/improve existing driver instead of coming with a duplicate. That's a standard upstream requirement, basically given on every upstreaming guide. Please watch old talk from Greg - "I Don’t Want Your Code!". > > v1: https://lore.kernel.org/all/20260519-qda-series-v1-0-b2d984c297f8@oss.qualc… > RFC: https://lore.kernel.org/dri-devel/20260224-qda-firstpost-v1-0-fe46a9c1a046@… > > Changes since v1 > ================ > > The v1 review raised two architectural objections and one correctness > issue; all three are resolved in v2: > > * Christian König (dma-buf maintainer) pointed out that the imported- > buffer path silently assumed the IOMMU maps every buffer as a single > contiguous range, which is not guaranteed. v2 walks the scatterlist > and cleanly rejects non-contiguous imports; contiguous imports (e.g. > CMA DMA-buf heap) are accepted. (patch 11) > > * Dmitry Baryshkov objected to three different buffer-passing formats > in the invoke IOCTL (DMA-BUF fd, direct/inline, DMA handle). v2 > passes only GEM handles; userspace imports any fd to a GEM handle > with DRM_IOCTL_PRIME_FD_TO_HANDLE before invoking. Packing and > overlap handling are left to userspace. (patch 12) > > * The memory manager (patch 07) used a fixed 16-entry array without > justification and leaked the device descriptor on teardown. v2 > allocates the array from the DT context-bank count (as Dmitry > suggested) and frees it correctly. > > User-space staging branch > ========================= > https://github.com/qualcomm/fastrpc/tree/accel/staging > > Key Features > ============ > > * Standard DRM accelerator interface via /dev/accel/accelN > * GEM-based buffer management with DMA-BUF import (PRIME) > * IOMMU-based memory isolation using per-process context banks > * FastRPC protocol implementation for DSP communication > * RPMsg transport layer for reliable message passing > * Support for all DSP domains (ADSP, CDSP, SDSP, GDSP) > * DRM IOCTL interface for DSP session management, buffer allocation, > and remote procedure invocation > > Architecture > ============ > > 1. DRM Accelerator Framework Integration > The driver registers as a DRM accel device, exposing a standard > /dev/accel/accelN character device node. This provides established > DRM infrastructure for device management, file operations, and > IOCTL dispatch. > > 2. Memory Management > Buffers are managed as GEM objects with PRIME support for DMA-BUF > import. This enables buffer sharing with other DRM drivers (GPU, > camera, video) using standard kernel mechanisms. Only contiguous > imports are accepted; the driver verifies contiguity at import time > rather than assuming it. > > 3. IOMMU Context Bank Management > IOMMU context banks (CBs) are represented as proper struct device > instances on a custom virtual bus (qda-compute-cb). Each CB device > is registered with the IOMMU subsystem and receives its own IOMMU > domain, enabling per-session address space isolation. The custom > bus was introduced because IOMMU context banks are synthetic > constructs — not real platform devices — and to ensure CB device > lifetime is strictly subordinate to the parent QDA device. > See also: https://lore.kernel.org/all/245d602f-3037-4ae3-9af9-d98f37258aae@oss.qualco… > > 4. Memory Manager Architecture > The memory manager maintains a registry of IOMMU devices in an > array sized to the number of context banks described in the device > tree, and coordinates per-process device assignment with reference- > counted lifetime management. The DMA-coherent backend allocates > buffers with SID-prefixed DMA addresses for DSP firmware > compatibility. > > 5. Transport Layer > RPMsg communication is handled in a dedicated transport layer > (qda_rpmsg.c), separate from the core DRM driver logic. > > 6. Code Organization > The driver is organized across multiple files (~4800 lines total): > * qda_drv.c: Core driver and DRM integration > * qda_rpmsg.c: RPMsg transport layer > * qda_cb.c: Context bank device management > * qda_compute_bus.c: Custom virtual bus for CB devices > * qda_gem.c: GEM object management > * qda_prime.c: DMA-BUF import (PRIME) > * qda_memory_manager.c: IOMMU device registry and allocation > * qda_memory_dma.c: DMA-coherent allocation backend > * qda_fastrpc.c: FastRPC protocol implementation > * qda_ioctl.c: IOCTL dispatch > > 7. UAPI Design > The driver exposes DRM-style IOCTLs defined in > include/uapi/drm/qda_accel.h, following DRM UAPI conventions > (__u32/__u64 types, C++ guard, GPL-2.0-only WITH Linux-syscall-note). > Buffer arguments are identified by GEM handles; the driver never > accepts DMA-BUF fds directly in any IOCTL. > > Patch Series Organization > ========================== > > Patch 01: MAINTAINERS entry > Patch 02: Driver documentation (Documentation/accel/qda/) > Patches 03-04: Core driver skeleton and compute bus > Patch 05: iommu: Register qda-compute-cb bus with IOMMU subsystem > Patches 06-07: CB device enumeration and memory manager > Patch 08: QUERY IOCTL and UAPI header > Patches 09-11: GEM buffer management and PRIME import > Patches 12-15: FastRPC protocol (invoke, session create/release, > map/unmap) > > Open Items > =========== > > 1. Device-Tree Compatible String > The QDA driver uses the same device-tree node structure and > properties as the existing fastrpc driver in drivers/misc/. A > mechanism is needed to allow the QDA driver to bind to its device > node independently of the fastrpc driver. > > The intended coexistence model is: platforms that require the > complete fastrpc feature set continue to use "qcom,fastrpc"; new > platforms where QDA's feature set is sufficient use a QDA-specific > compatible string. New feature development is directed toward QDA. > > The options under consideration are: > > a) Add a new "qcom,qda" compatible string to the existing > qcom,fastrpc.yaml binding, since the DT node structure and > properties are identical. No > > b) Introduce a separate qcom,qda.yaml binding that references or > inherits the fastrpc binding properties. No > > Seeking guidance from DT binding maintainers on the preferred > approach. Grow existing driver. You do not get new driver, you do not get new bindings. Best regards, Krzysztof

1 month

Re: [PATCH v2 00/15] accel/qda: Qualcomm DSP Accelerator driver

by Krzysztof Kozlowski

1 month

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