search for: v4l2

...ent hints. Namely, the queue consistency (memory coherency) user-space hint because, as it turned out, the kernel implementation of this feature was misusing DMA_ATTR_NON_CONSISTENT. The patch revers both kernel and user space parts: removes the DMA consistency attr functions, rollbacks changes to v4l2_requestbuffers, v4l2_create_buffers structures and corresponding UAPI functions (plus compat32 layer) and cleanups the documentation. Signed-off-by: Christoph Hellwig <hch at lst.de> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky at gmail.com> Signed-off-by: Christoph Hellwig &l...

On Wed, Aug 19, 2020 at 01:16:51PM +0200, Tomasz Figa wrote: > Hi Christoph, > > On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch at lst.de> wrote: > > > > The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, > > Could you explain what makes you think it's unused? It's a feature of > the UAPI generally supported by the videobuf2 framework and relied on > by Chromium OS to get any kind of reasonable performance when > accessing V...

The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, and causes weird gymanstics with the DMA_ATTR_NON_CONSISTENT flag, which is unimplemented except on PARISC and some MIPS configs, and about to be removed. Signed-off-by: Christoph Hellwig <hch at lst.de> --- .../userspace-api/media/v4l/buf...

...Aug 19, 2020 at 3:55 PM Christoph Hellwig <hch at lst.de> wrote: > > On Wed, Aug 19, 2020 at 01:16:51PM +0200, Tomasz Figa wrote: > > Hi Christoph, > > > > On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch at lst.de> wrote: > > > > > > The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, > > > > Could you explain what makes you think it's unused? It's a feature of > > the UAPI generally supported by the videobuf2 framework and relied on > > by Chromium OS to get any kind of reasonable performance wh...

Hi Tomasz, On 2020-08-19 12:16, Tomasz Figa wrote: > Hi Christoph, > > On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch at lst.de> wrote: >> >> The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, > > Could you explain what makes you think it's unused? It's a feature of > the UAPI generally supported by the videobuf2 framework and relied on > by Chromium OS to get any kind of reasonable performance when > accessing V...

...Tomasz Figa wrote: > > > Could you explain what makes you think it's unused? It's a feature of > > > the UAPI generally supported by the videobuf2 framework and relied on > > > by Chromium OS to get any kind of reasonable performance when > > > accessing V4L2 buffers in the userspace. > > > > Because it doesn't do anything except on PARISC and non-coherent MIPS, > > so by definition it isn't used by any of these media drivers. > > It's still an UAPI feature, so we can't simply remove the flag, it > must stay t...

...> > > > Could you explain what makes you think it's unused? It's a feature of > > > > the UAPI generally supported by the videobuf2 framework and relied on > > > > by Chromium OS to get any kind of reasonable performance when > > > > accessing V4L2 buffers in the userspace. > > > > > > Because it doesn't do anything except on PARISC and non-coherent MIPS, > > > so by definition it isn't used by any of these media drivers. > > > > It's still an UAPI feature, so we can't simply remove the...

On Thu, Aug 20, 2020 at 12:05:29PM +0200, Tomasz Figa wrote: > The UAPI and V4L2/videobuf2 changes are in good shape and the only > wrong part is the use of DMA API, which was based on an earlier email > guidance anyway, and a change to the synchronization part . I find > conclusions like the above insulting for people who put many hours > into designing and impleme...

On Thu, Aug 20, 2020 at 12:24:31PM +0200, Tomasz Figa wrote: > > Of course this still uses the scatterlist structure with its annoying > > mix of input and output parametes, so I'd rather not expose it as > > an official API at the DMA layer. > > The problem with the above open coded approach is that it requires > explicit handling of the non-IOMMU and IOMMU cases

...phy <robin.murphy at arm.com> wrote: >> >> Hi Tomasz, >> >> On 2020-08-19 12:16, Tomasz Figa wrote: >>> Hi Christoph, >>> >>> On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch at lst.de> wrote: >>>> >>>> The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, >>> >>> Could you explain what makes you think it's unused? It's a feature of >>> the UAPI generally supported by the videobuf2 framework and relied on >>> by Chromium OS to get any kind of reasonable pe...

Hi Christoph, On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch at lst.de> wrote: > > The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, Could you explain what makes you think it's unused? It's a feature of the UAPI generally supported by the videobuf2 framework and relied on by Chromium OS to get any kind of reasonable performance when accessing V4L2 buffers in the usersp...

...> Could you explain what makes you think it's unused? It's a feature of > > > > > the UAPI generally supported by the videobuf2 framework and relied on > > > > > by Chromium OS to get any kind of reasonable performance when > > > > > accessing V4L2 buffers in the userspace. > > > > > > > > Because it doesn't do anything except on PARISC and non-coherent MIPS, > > > > so by definition it isn't used by any of these media drivers. > > > > > > It's still an UAPI feature, so we can&...

On Wed, Aug 19, 2020 at 02:49:01PM +0200, Tomasz Figa wrote: > With the default config it doesn't, but with > CONFIG_DMA_NONCOHERENT_CACHE_SYNC enabled it makes dma_pgprot() keep > the pgprot value as is, without enforcing coherence attributes. Which isn't selected on arm64, and that is for a good reason. > AFAIK dma_cache_sync() isn't the only way to perform the cache

On Wed, Aug 19, 2020 at 04:11:52PM +0200, Tomasz Figa wrote: > > > By the way, as a videobuf2 reviewer, I'd appreciate being CC'd on any > > > series related to the subsystem-facing DMA API changes, since > > > videobuf2 is one of the biggest users of it. > > > > The cc list is too long - I cc lists and key maintainers. As a reviewer > > should

On Thu, Aug 20, 2020 at 6:45 AM Christoph Hellwig <hch at lst.de> wrote: > > On Wed, Aug 19, 2020 at 04:11:52PM +0200, Tomasz Figa wrote: > > > > By the way, as a videobuf2 reviewer, I'd appreciate being CC'd on any > > > > series related to the subsystem-facing DMA API changes, since > > > > videobuf2 is one of the biggest users of it. >

On Thu, Aug 20, 2020 at 07:33:48PM +0200, Tomasz Figa wrote: > > It wasn't meant to be too insulting, but I found this out when trying > > to figure out how to just disable it. But it also ends up using > > the actual dma attr flags for it's own consistency checks, so just > > not setting the flag did not turn out to work that easily. > > > > Yes,

On Thu, Aug 20, 2020 at 7:02 AM Christoph Hellwig <hch at lst.de> wrote: > > On Wed, Aug 19, 2020 at 03:07:04PM +0100, Robin Murphy wrote: > >> FWIW, I asked back in time what the plan is for non-coherent > >> allocations and it seemed like DMA_ATTR_NON_CONSISTENT and > >> dma_sync_*() was supposed to be the right thing to go with. [2] The > >> same

On Thu, Aug 20, 2020 at 6:54 PM Christoph Hellwig <hch at lst.de> wrote: > > On Thu, Aug 20, 2020 at 12:05:29PM +0200, Tomasz Figa wrote: > > The UAPI and V4L2/videobuf2 changes are in good shape and the only > > wrong part is the use of DMA API, which was based on an earlier email > > guidance anyway, and a change to the synchronization part . I find > > conclusions like the above insulting for people who put many hours > > into d...

...t; >> > >> Hi Tomasz, > >> > >> On 2020-08-19 12:16, Tomasz Figa wrote: > >>> Hi Christoph, > >>> > >>> On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch at lst.de> wrote: > >>>> > >>>> The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, > >>> > >>> Could you explain what makes you think it's unused? It's a feature of > >>> the UAPI generally supported by the videobuf2 framework and relied on > >>> by Chromium OS to get any k...

On Wed, Aug 19, 2020 at 3:57 PM Christoph Hellwig <hch at lst.de> wrote: > > On Wed, Aug 19, 2020 at 02:49:01PM +0200, Tomasz Figa wrote: > > With the default config it doesn't, but with > > CONFIG_DMA_NONCOHERENT_CACHE_SYNC enabled it makes dma_pgprot() keep > > the pgprot value as is, without enforcing coherence attributes. > > Which isn't selected on