Hi all,
The followings are Samsung S.LSI's requirement for unified memory manager.
1. User space API
1.1. New memory management(MM) features should includes followings
to the user space.: UMP
A. user space API for memory allocation from system memory: UMP
Any user process can allocate memory from kernel space by new MM model.
B. user space API for cache operations: flush, clean, invalidate
Any user process can do cache operation on the allocated memory.
C. user space API for mapping memory attribute as cacheable
When the system memory mapped into the user space,
user process can set its property as cacheable.
D. user space API for mapping memory attribute as non-cacheable
When the system memory mapped into the user space,
user process can set its property as non-cacheable.
1.2. Inter-process memory sharing: UMP
New MM features should provide memory sharing between user process.
A. Memory allocated by user space can be shared between user processes.
B. Memory allocated by kernel space can be shared between user processes.
2. Kernel space API
New MM features should includes followings to the kernel space.: CMA, VCMM
2-1. Physically memory allocator
A. kernel space API for contiguous memory allocation: CMA(*)
B. kernel space API for non-contiguous memory allocation: VCMM (*)
C. start address alignment: CMA, VCMM
D. selectable allocating region: CMA
*refer to the bottom's extension.
2-2. Device virtual address management: VCMM
New MM features should provide
the way of managing device virtual memory address as like followings:
A. IOMMU(System MMU) support
IOMMU is a kind of memory MMU, but IOMMU is dedicated for each device.
B. device virtual address mapping for each device
C. virtual memory allocation
D. mapping / remapping between phys and device virtual address
E. dedicated device virtual address space for each device
F. address translation between address space
U.V
/ \
K.V - P.A
\ /
D.V
U.V: User space address
K.A: Kernel space address
P.A: Physical address
D.V: Device virtual address
3. Extensions
A. extension for custom physical memory allocator
B. extension for custom MMU controller
-------------------------------------------------------------------------
You can find the implementation in the following git repository.
http://git.kernel.org/?p=linux/kernel/git/kki_ap/linux-2.6-
samsung.git;a=tree;hb=refs/heads/2.6.36-samsung
1. UMP (Unified Memory Provider)
- The UMP is an auxiliary component which enables memory to be shared
across different applications, drivers and hardware components.
- http://blogs.arm.com/multimedia/249-making-the-mali-gpu-device-driver-
open-source/page__cid__133__show__newcomment/
- Suggested by ARM, Not submitted yet.
- implementation
drivers/media/video/samsung/ump/*
2. VCMM (Virtual Contiguous Memory Manager)
- The VCMM is a framework to deal with multiple IOMMUs in a system
with intuitive and abstract objects
- Submitted by Michal Nazarewicz @Samsung-SPRC
- Also submitted by KyongHo Cho @Samsung-SYS.LSI
- http://article.gmane.org/gmane.linux.kernel.mm/56912/match=vcm
- implementation
include/linux/vcm.h
include/linux/vcm-drv.h
mm/vcm.c
arch/arm/plat-s5p/s5p-vcm.c
arch/amr/plat-s5p/include/plat/s5p-vcm.h
3. CMA (Contiguous Memory Allocator)
- The Contiguous Memory Allocator (CMA) is a framework, which allows
setting up a machine-specific configuration for physically-contiguous
memory management. Memory for devices is then allocated according
to that configuration.
- http://lwn.net/Articles/396702/
- http://www.spinics.net/lists/linux-media/msg26486.html
- Submitted by Michal Nazarewicz @Samsung-SPRC
- implementation
mm/cma.c
include/linux/cma.h
4. SYS.MMU
- System MMU supports address transition from VA to PA.
- http://thread.gmane.org/gmane.linux.kernel.samsung-soc/3909
- Submitted by Sangbeom Kim
- Merged by Kukjin Kim, ARM/S5P ARM ARCHITECTURES maintainer
- implementation
arch/arm/plat-s5p/sysmmu.c
arch/arm/plat-s5p/include/plat/sysmmu.h
I think the recent discussions on linaro-mm-sig and the BoF last week
at ELC have been quite productive, and at least my understanding
of the missing pieces has improved quite a bit. This is a list of
things that I think need to be done in the kernel. Please complain
if any of these still seem controversial:
1. Fix the arm version of dma_alloc_coherent. It's in use today and
is broken on modern CPUs because it results in both cached and
uncached mappings. Rebecca suggested different approaches how to
get there.
2. Implement dma_alloc_noncoherent on ARM. Marek pointed out
that this is needed, and it currently is not implemented, with
an outdated comment explaining why it used to not be possible
to do it.
3. Convert ARM to use asm-generic/dma-mapping-common.h. We need
both IOMMU and direct mapped DMA on some machines.
4. Implement an architecture independent version of dma_map_ops
based on the iommu.h API. As Joerg mentioned, this has been
missing for some time, and it would be better to do it once
than for each IOMMU separately. This is probably a lot of work.
5. Find a way to define per-device IOMMUs, if that is not actually
possible already. We had conflicting statements for this.
6. Implement iommu_ops for each of the ARM platforms that has
an IOMMU. Needs some modifications for MSM and a rewrite for
OMAP. Implementation for Samsung is under work.
7. Extend the dma_map_ops to have a way for mapping a buffer
from dma_alloc_{non,}coherent into user space. We have not
discussed that yet, but after thinking this for some time, I
believe this would be the right approach to map buffers into
user space from code that doesn't care about the underlying
hardware.
After all these are in place, building anything on top of
dma_alloc_{non,}coherent should be much easier. The question
of passing buffers between V4L and DRM is still completely
unsolved as far as I can tell, but that discussion might become
more focused if we can agree on the above points and assume
that it will be done.
I expect that I will have to update the list above as people
point out mistakes in my assumptions.
Arnd
On Wednesday 27 April 2011 23:31:06 Benjamin Herrenschmidt wrote:
> On Thu, 2011-04-21 at 21:29 +0200, Arnd Bergmann wrote:
> > 7. Extend the dma_map_ops to have a way for mapping a buffer
> >
> > from dma_alloc_{non,}coherent into user space. We have not
> > discussed that yet, but after thinking this for some time, I
> > believe this would be the right approach to map buffers into
> > user space from code that doesn't care about the underlying
> > hardware.
>
> Yes. There is a dma_mmap_coherent() call that's not part of the "Real"
> API but is implemented by some archs and used by Alsa (I added support
> for it on powerpc recently).
>
> Maybe that should go into the dma ops.
>
> The question remains, if we ever want to do more complex demand-paged
> operations, should we also expose a lower level set of functions to get
> struct page out of a dma_alloc_coherent() allocation and to get the
> pgprot for the user dma mapping ?
>
> > After all these are in place, building anything on top of
> > dma_alloc_{non,}coherent should be much easier. The question
> > of passing buffers between V4L and DRM is still completely
> > unsolved as far as I can tell, but that discussion might become
> > more focused if we can agree on the above points and assume
> > that it will be done.
>
> My gut feeling is that it should be done by having V4L use DRM buffers
> in the first place...
V4L2 needs to capture data to a wide variety of memory locations (system
memory when you just want to process the data using the CPU, frame buffer
memory, contiguous buffers that will be passed to a DSP for video encoding,
GPU textures, ...). To allow those use cases (and more) the V4L2 API provides
two ways to handle data buffers: applications can request the driver to
allocate memory internally, and them mmap() the buffers to userspace, or pass
arbitrary memory pointers (and sizes) to the driver to be used as video
capture buffers.
In the first case drivers will allocate memory depending on their
requirements. This could mean vmalloc_user() for USB drivers that use memcpy()
in the kernel, vmalloc() for hardware that support SG-lists or IOMMUs,
dma_alloc_coherent() for drivers that need contiguous memory, ...
In the second case the driver will verify that the memory it receives from the
application matches its requirements (regarding contiguousness for instance)
and will then use that memory.
I think we could target the second case only if we want to share buffers
between V4L and DRM, as V4L2 (unlike DRM) is already pretty good at using
buffers it didn't allocate itself. The current API will need to be extended to
pass an opaque buffer handle instead of a memory address, as we want to avoid
requiring a userspace mapping for the buffer when not necessary. That's the
whole point of the initial memory management discussion.
We will of course need to make sure that the DRM buffers fullfil the V4L2
needs.
> > I expect that I will have to update the list above as people
> > point out mistakes in my assumptions.
--
Regards,
Laurent Pinchart
