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2529 discussions

ashmem - mmap deadlock with mmap_sem & ashmem_mutex

by Shankar Brahadeeswaran

Hi, I'm working on Android Linux Kernel Vesion 3.0.15 and seeing a "deadlock" in the ashmem driver, while handling mmap request. I seek your support in finding the correct fix. The locks that involved in the dead lock are 1) mm->mmap_sem 2) ashmem_mutex The following is the sequence of events that leads to the deadlock. There are two threads A and B that belong to the same process (system_server) and hence share the mm struct. A1) In the A's context an mmap system call is made with an fd of ashmem A2) The system call sys_mmap_pgoff acquires the mmap_sem of the "mm" and sleeps before calling the .mmap of ashmem i.e before calling ashmem_mmap Now the thread B runs and proceeds to do the following B1) In the B's context ashmem ioctl with option ASHMEM_SET_NAME is called. B2) Now the code proceeds to acquire the ashmem_mutex and performs a "copy_from_user" B3) copy_from_user raises a valid exception to copy the data from user space and proceeds to handle it gracefully, do_DataAbort --> do_page_fault B4) In do_page_fault it finds that the mm->mmap_sem is not available (Note A & B share the mm) since A has it and sleeps Now the thread A runs again A3) It proceeds to call ashmem_mmap and tries to acquired ashmem_mutex, which is not available (is with B) and sleeps. Now A has acquired mmap_sem and waits for B to release ashmem_mutex B has acquired ashmem_mutex and waits for the mmap_sem to be available, which is held by A This creates a dead lock in the system. I'm not sure how to use these locks in such a way as to prevent this scenario. Any suggestions would be of great help. Workaround: One possible work around is to replace the mutex_lock call made in the ashmem_mmap with mutex_trylock and if it fails, wait for few milliseconds and try back for few iterations and finally give up after few iterations. This will bring the system out deadlock if this scneario happens. I myself feel that this suggestion is not clean. But I'm unable to think of anything. Is there any suggestion to avoid this scenario. Warm Regards, Shankar

11 years, 10 months

[PATCH 0/2] ARM: dma-mapping: add highmem support for coherent allocation

by Marek Szyprowski

Hello, This is the last missing piece to let us efficiently use large DMA buffers on systems with lots of memory, which have support for himem enabled. The first patch adds support for CMA regions placed in high memory zones, the second one also enables allocations of individual pages from high memory zone for IOMMU-mapped devices. Those two changes let us to significantly save low memory for other tasks. Best regards Marek Szyprowski Samsung Poland R&D Center Patch summary: Marek Szyprowski (2): ARM: dma-mapping: add support for CMA regions placed in highmem zone ARM: dma-mapping: use himem for DMA buffers for IOMMU-mapped devices arch/arm/mm/dma-mapping.c | 70 +++++++++++++++++++++++++++++++++------------ 1 file changed, 52 insertions(+), 18 deletions(-) -- 1.7.9.5

11 years, 10 months

Re: [Linaro-mm-sig] CDF meeting @FOSDEM report

by Tomi Valkeinen

Hi, On 2013-02-06 00:27, Laurent Pinchart wrote: > Hello, > > We've hosted a CDF meeting at the FOSDEM on Sunday morning. Here's a summary > of the discussions. Thanks for the summary. I've been on a longish leave, and just got back, so I haven't read the recent CDF discussions on lists yet. I thought I'll start by replying to this summary first =). > 0. Abbreviations > ---------------- > > DBI - Display Bus Interface, a parallel video control and data bus that > transmits data using parallel data, read/write, chip select and address > signals, similarly to 8051-style microcontroller parallel busses. This is a > mixed video control and data bus. > > DPI - Display Pixel Interface, a parallel video data bus that transmits data > using parallel data, h/v sync and clock signals. This is a video data bus > only. > > DSI - Display Serial Interface, a serial video control and data bus that > transmits data using one or more differential serial lines. This is a mixed > video control and data bus. In case you'll re-use these abbrevs in later posts, I think it would be good to mention that DPI is a one-way bus, whereas DBI and DSI are two-way (perhaps that's implicit with control bus, though). > 1. Goals > -------- > > The meeting started with a brief discussion about the CDF goals. > > Tomi Valkeinin and Tomasz Figa have sent RFC patches to show their views of > what CDF could/should be. Many others have provided very valuable feedback. > Given the early development stage propositions were sometimes contradictory, > and focused on different areas of interest. We have thus started the meeting > with a discussion about what CDF should try to achieve, and what it shouldn't. > > CDF has two main purposes. The original goal was to support display panels in > a platform- and subsystem-independent way. While mostly useful for embedded > systems, the emergence of platforms such as Intel Medfield and ARM-based PCs > that blends the embedded and PC worlds makes panel support useful for the PC > world as well. > > The second purpose is to provide a cross-subsystem interface to support video > encoders. The idea originally came from a generalisation of the original RFC > that supported panels only. While encoder support is considered as lower > priority than display panel support by developers focussed on display > controller driver (Intel, Renesas, ST Ericsson, TI), companies that produce > video encoders (Analog Devices, and likely others) don't share that point of > view and would like to provide a single encoder driver that can be used in > both KMS and V4L2 drivers. What is an encoder? Something that takes a video signal in, and lets the CPU store the received data to memory? Isn't that a decoder? Or do you mean something that takes a video signal in, and outputs a video signal in another format? (transcoder?) If the latter, I don't see them as lower priority. If we use CDF also for SoC internal components (which I think would be great), then every OMAP board has transcoders. I'm not sure about the vocabulary on this area, but a normal OMAP scenario could have a following video pipeline: 1. encoder (OMAP's DISPC, reads pixels from memory and outputs parallel RGB) 2. transcoder (OMAP's DSI, gets parallel RGB and outputs DSI) 3. transcoder (external DSI-to-LVDS chip) 4. panel (LVDS panel) Even in the case where a panel would be connected directly to the OMAP, there would be the internal transcoder. > 2. Subsystems > ------------- > > Display panels are used in conjunction with FBDEV and KMS drivers. There was > to the audience knowledge no V4L2 driver that needs to explicitly handle > display panels. Even though at least one V4L2 output drivers (omap_vout) can > output video to a display panel, it does so in conjunction with the KMS and/or > FBDEV APIs that handle panel configuration. Panels are thus not exposed to > V4L2 drivers. Hmm, I'm no expert on omap_vout, but it doesn't use KMS nor omapfb. It uses omapdss directly, and thus accesses the panels. That said, I'm fine with leaving omap_vout out from the equation. > 3. KMS Extensions > ----------------- > > The usefulness of V4L2 for output devices was questioned, and the possibility > of using KMS for complex video devices usually associated with V4L2 was > raised. The TI DaVinci 8xxx family is an example of chips that could benefit > from KMS support. > > The KMS API is lacking support for deep-pipelining ("framebuffers" that are > sourced from a data stream instead of a memory buffer) today. Extending the > KMS API with deep-pipelining support was considered as a sensible goal that > would mostly require the creation of a new KMS source object. Exposing the > topology of the whole device would then be handled by the Media Controller > API. Isn't there also the problem that KSM doesn't support arbitrarily long chains of display devices? That actually sounds more like "deep-pipelining" than what you said, getting the source data from a data stream. > 5. Bus Model > ------------ > > Display panels are connected to a video bus that transmits video data and > optionally to a control bus. Those two busses can be separate physical > interfaces or combined into a single physical interface. > > The Linux device model represents the system as a tree of devices (not to be > confused by the device tree, abreviated as DT). The tree is organized around > control busses, with every device being a child of its control bus master. For > instance an I2C device will be a child of its I2C controller device, which can > itself be a child of its parent PCI device. > > Display panels will be represented as Linux devices. They will have a single > parent from the Linux device model point of view, but will be potentially > connected to multiple physical busses. CDF thus needs to define what bus to > select as the Linux parent bus. > > In theory any physical bus that the device is attached to can be selected as > the parent bus. However, selecting a video data bus would depart from the > traditional Linux device model that uses control busses only. This caused > concern among several people who argued that not presenting the device to the > kernel as attached to its control bus would bring issues in embedded system. > Unlike on PC systems where the control bus master is usually the same physical > device as the data bus master, embedded systems are made of a potentially > complex assembly of completely unrelated devices. Not representing an I2C- > controlled panel as a child of its I2C master in DT was thus frown upon, even > though no clear agreement was reached on the subject. I've been thinking that a good rule of thumb would be that the device must be somewhat usable after the parent bus is ready. So for, say, DPI+SPI panel, when the SPI is set up the driver can send messages to the panel, perhaps read an ID or such, even if the actual video cannot be shown yet (presuming DPI bus is still missing). Of course there are the funny cases, as always. Say, a DSI panel, controlled via i2c, and the panel gets its functional clock from the DSI bus's clock. In that case both busses need to be up and running before the panel can do anything. > - Combined video and control busses > > When the two busses are combined in a single physical bus the panel device > will obviously be represented as a child of that single physical bus. > > In such cases the control bus could expose video bus control methods. This > would remove the need for a video source as proposed by Tomi Valkeinen in his > CDF model. However, if the bus can be used for video data transfer in > combination with a different control bus, a video source corresponding to the > data bus will be needed. I think this is always the case. If a bus can be used for control and video data, you can always use it only for video data. > No decision has been taken on whether to use a video source in addition to the > control bus in the combined busses case. Experimentation will be needed, and > the right solution might depend on the bus type. > > - Multiple control busses > > One panel was mentioned as being connected to a DSI bus and an I2C bus. The > DSI bus is used for both control and video, and the I2C bus for control only. > configuring the panel requires sending commands through both DSI and I2C. The I have luckily not encountered such a device. However, many of the DSI devices do have i2c control as an option. From the device's point of view, both can be used at the same time, but I think usually it's saner to just pick one and use it. The driver for the device should support both control busses, though. Probably 99% of the driver code is common for both cases. > 6. Miscellaneous > ---------------- > > - If the OMAP3 DSS driver is used as a model for the DSI support > implementation, Daniel Vetter requested the DSI bus lock semaphore to be > killed as it prevents lockdep from working correctly (reference needed ;-)). I don't think OMAP DSS should be used as a model. It has too much legacy crap that should be rewritten. However, it can be used as a reference to see what kind of features are needed, as it does support both video and command mode DSI modes, and has been used with many different kinds of DSI panels and DSI transcoders. As for the semaphore, sure, it can be removed, although I'm not aware of this lockdep problem. If there's a problem it should be fixed in any case. > - Do we need to support chaining several encoders ? We can come up with > several theoretical use cases, some of them probably exist in real hardware, > but the details are still a bit fuzzy. If encoder means the same as the "transcoder" term I used earlier, then yes, I think so. As I wrote, I'd like to model the OMAP DSS internal components with CDF. The internal IP blocks are in no way different than external IP blocks, they just happen to be integrated into OMAP. The same display IPs are used with multiple different TI SoCs. Also, the IPs vary between TI SoCs (for ex, omap2 doesn't have DSI, omap3 has one DSI, omap4 has two DSIs), so we'll anyway need to have some kind of dynamic system inside omapdss driver. If I can't use CDF for that, I'll need to implement a custom one, which I believe would resemble CDF in many ways. I'm guessing that having multiple external transcoders is quite rare on production hardware, but is a very useful feature with development boards. It's not just once or twice that we've used a transcoder or two between a SoC and a panel, because we haven't had the final panel yet. Also, sometimes there are small simple chips in the video pipeline, that do things like level shifting or ESD protection. In some cases these chips just work automatically, but in some cases one needs to setup regulators and gpios to get them up and running (for example, http://www.ti.com/product/tpd12s015). And if that's the case, then I believe having a CDF "transcoder" driver for the chip is the easiest solution. Tomi

11 years, 10 months

[RESEND][PATCH] ARM: dma-mapping: Add maximum alignment order for dma iommu buffers

by Seung-Woo Kim

Alignment order for a dma iommu buffer is set by buffer size. For large buffer, it is a waste of iommu address space. So configurable parameter to limit maximum alignment order can reduce the waste. Signed-off-by: Seung-Woo Kim <sw0312.kim(a)samsung.com> Signed-off-by: Kyungmin.park <kyungmin.park(a)samsung.com> --- There was stupid misses in previous patch, so I resend fixed version. arch/arm/Kconfig | 21 +++++++++++++++++++++ arch/arm/mm/dma-mapping.c | 3 +++ 2 files changed, 24 insertions(+), 0 deletions(-) diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 67874b8..4e89112 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -75,6 +75,27 @@ config ARM_DMA_USE_IOMMU select ARM_HAS_SG_CHAIN select NEED_SG_DMA_LENGTH +if ARM_DMA_USE_IOMMU + +config ARM_DMA_IOMMU_ALIGNMENT + int "Maximum PAGE_SIZE order of alignment for DMA IOMMU buffers" + range 4 9 + default 8 + help + DMA mapping framework by default aligns all buffers to the smallest + PAGE_SIZE order which is greater than or equal to the requested buffer + size. This works well for buffers up to a few hundreds kilobytes, but + for larger buffers it just a waste of address space. Drivers which has + relatively small addressing window (like 64Mib) might run out of + virtual space with just a few allocations. + + With this parameter you can specify the maximum PAGE_SIZE order for + DMA IOMMU buffers. Larger buffers will be aligned only to this + specified order. The order is expressed as a power of two multiplied + by the PAGE_SIZE. + +endif + config HAVE_PWM bool diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index 076c26d..4cce854 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -1002,6 +1002,9 @@ static inline dma_addr_t __alloc_iova(struct dma_iommu_mapping *mapping, unsigned int count, start; unsigned long flags; + if (order > CONFIG_ARM_DMA_IOMMU_ALIGNMENT) + order = CONFIG_ARM_DMA_IOMMU_ALIGNMENT; + count = ((PAGE_ALIGN(size) >> PAGE_SHIFT) + (1 << mapping->order) - 1) >> mapping->order; -- 1.7.4.1

11 years, 10 months

[PATCH 0/7] cross-device reservation for dma-buf support

by Maarten Lankhorst

So I'm resending the patch series for reservations. This is identical to my git tree at http://cgit.freedesktop.org/~mlankhorst/linux/ Some changes have been made since my last version. Most notably is the use of mutexes now instead of creating my own lock primitive, that would end up being duplicate anyway. The git tree also has a version of i915 and radeon working together like that. It's probably a bit hacky, but it works on my macbook pro 8.2. :) I haven't had any reply on the mutex extensions when I sent them out separately, so I'm including it in the series. The idea is that for lockdep purposes, the seqno is tied to a locking a class. This locking class it not exclusive, but as can be seen from the last patch in the series, it catches all violations we care about.

11 years, 10 months

CDF discussions at FOSDEM

by Laurent Pinchart

Hi everybody, Would anyone be interested in meeting at the FOSDEM to discuss the Common Display Framework ? There will be a CDF meeting at the ELC at the end of February, the FOSDEM would be a good venue for European developers. -- Regards, Laurent Pinchart

11 years, 10 months

[RFC] ARM: dma-mapping: Return 0 if no ->set_dma_mask()

by Hiroshi Doyu

struct dma_map_ops iommu_ops doesn't have ->set_dma_mask, which causes crash when dma_set_mask() is called from some driver. Signed-off-by: Hiroshi Doyu <hdoyu(a)nvidia.com> --- arch/arm/include/asm/dma-mapping.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h index a58e0f5..95328bf 100644 --- a/arch/arm/include/asm/dma-mapping.h +++ b/arch/arm/include/asm/dma-mapping.h @@ -32,7 +32,11 @@ static inline void set_dma_ops(struct device *dev, struct dma_map_ops *ops) static inline int dma_set_mask(struct device *dev, u64 mask) { - return get_dma_ops(dev)->set_dma_mask(dev, mask); + struct dma_map_ops *ops = get_dma_ops(dev); + + if (ops->set_dma_mask) + return ops->set_dma_mask(dev, mask); + return 0; } #ifdef __arch_page_to_dma -- 1.7.9.5

11 years, 11 months

Common Display Framework BoF at ELC

by Jesse Barker

Hi all, I've just confirmed the schedule for ELC ( http://events.linuxfoundation.org/events/embedded-linux-conference/schedule), and we're on for Thursday at 4pm. I requested 2 slots to give us some flexibility (that's the "Part I & Part II" on the schedule). Whether you are attending the rest of ELC or not, if you care about CDF, please come by. cheers, Jesse

11 years, 11 months

[RFC] ARM: dma-mapping: Add DMA attribute to skip iommu mapping

by Abhinav Kochhar

Adding a new dma attribute which can be used by the platform drivers to avoid creating iommu mappings. In some cases the buffers are allocated by display controller driver using dma alloc apis but are not used for scanout. Though the buffers are allocated by display controller but are only used for sharing among different devices. With this attribute the platform drivers can choose not to create iommu mapping at the time of buffer allocation and only create the mapping when they access this buffer. Change-Id: I2178b3756170982d814e085ca62474d07b616a21 Signed-off-by: Abhinav Kochhar <abhinav.k(a)samsung.com> --- arch/arm/mm/dma-mapping.c | 8 +++++--- include/linux/dma-attrs.h | 1 + 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index c0f0f43..e73003c 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -1279,9 +1279,11 @@ static void *arm_iommu_alloc_attrs(struct device *dev, size_t size, if (!pages) return NULL; - *handle = __iommu_create_mapping(dev, pages, size); - if (*handle == DMA_ERROR_CODE) - goto err_buffer; + if (!dma_get_attr(DMA_ATTR_NO_IOMMU_MAPPING, attrs)) { + *handle = __iommu_create_mapping(dev, pages, size); + if (*handle == DMA_ERROR_CODE) + goto err_buffer; + } if (dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs)) return pages; diff --git a/include/linux/dma-attrs.h b/include/linux/dma-attrs.h index c8e1831..1f04419 100644 --- a/include/linux/dma-attrs.h +++ b/include/linux/dma-attrs.h @@ -15,6 +15,7 @@ enum dma_attr { DMA_ATTR_WEAK_ORDERING, DMA_ATTR_WRITE_COMBINE, DMA_ATTR_NON_CONSISTENT, + DMA_ATTR_NO_IOMMU_MAPPING, DMA_ATTR_NO_KERNEL_MAPPING, DMA_ATTR_SKIP_CPU_SYNC, DMA_ATTR_FORCE_CONTIGUOUS, -- 1.7.8.6

11 years, 11 months

Attendance at ELC San Francisco

by Jesse Barker

Hi all, With all of the attention that the Common Display Framework is getting, I was wondering if it was worth having a BoF discussion at ELC next month in San Francisco. This will be only a couple of weeks after FOSDEM, but given the pace that things seem to be moving, that could be a great opportunity either to have a follow-on discussion, or simply to involve a slightly different cross-section of the community in a face-to-face discussion. If folks could let me know that they'll be at ELC and are interested in a BoF there, I'll look into getting it set up. cheers, Jesse

11 years, 11 months

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