From: Tomasz Figa <tfiga@chromium.org>
To: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Hans Verkuil <hans.verkuil@cisco.com>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Kyungmin Park <kyungmin.park@samsung.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Sakari Ailus <sakari.ailus@iki.fi>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Pawel Osciak <posciak@chromium.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH 12/15] videobuf2: add begin/end cpu_access callbacks to dma-sg
Date: Mon, 3 Feb 2020 19:04:40 +0900 [thread overview]
Message-ID: <CAAFQd5BGA-mnirgwQJP_UHkNzpVvf19xeRu-n7GLQci8nYGB2A@mail.gmail.com> (raw)
In-Reply-To: <c23618a9-4bf8-1d9a-6e52-d616c79ff289@xs4all.nl>
On Thu, Jan 30, 2020 at 9:18 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>
> On 1/30/20 12:02 PM, Tomasz Figa wrote:
> > On Tue, Jan 28, 2020 at 5:36 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
> >>
> >> On 1/28/20 5:38 AM, Tomasz Figa wrote:
> >>> On Fri, Jan 10, 2020 at 7:13 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
> >>>>
> >>>> On 12/17/19 4:20 AM, Sergey Senozhatsky wrote:
> >>>>> Provide begin_cpu_access() and end_cpu_access() dma_buf_ops
> >>>>> callbacks for cache synchronisation on exported buffers.
> >>>>>
> >>>>> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> >>>>> ---
> >>>>> .../media/common/videobuf2/videobuf2-dma-sg.c | 22 +++++++++++++++++++
> >>>>> 1 file changed, 22 insertions(+)
> >>>>>
> >>>>> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> >>>>> index 6db60e9d5183..bfc99a0cb7b9 100644
> >>>>> --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> >>>>> +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
> >>>>> @@ -470,6 +470,26 @@ static void vb2_dma_sg_dmabuf_ops_release(struct dma_buf *dbuf)
> >>>>> vb2_dma_sg_put(dbuf->priv);
> >>>>> }
> >>>>>
> >>>>
> >>>> There is no corresponding vb2_sg_buffer_consistent function here.
> >>>>
> >>>> Looking more closely I see that vb2_dma_sg_alloc doesn't pass the dma_attrs
> >>>> argument to dma_map_sg_attrs, thus V4L2_FLAG_MEMORY_NON_CONSISTENT has no
> >>>> effect on dma-sg buffers.
> >>>
> >>> videobuf2-dma-sg allocates the memory using the page allocator
> >>> directly, which means that there is no memory consistency guarantee.
> >>>
> >>>>
> >>>> Is there a reason why dma_attrs isn't passed on to dma_map_sg_attrs()?
> >>>>
> >>>
> >>> V4L2_FLAG_MEMORY_NON_CONSISTENT is a flag for dma_alloc_attrs(). It
> >>> isn't supposed to do anything for dma_map_sg_attrs(), which is only
> >>> supposed to create the device (e.g. IOMMU) mapping for already
> >>> allocated memory.
> >>
> >> Ah, right.
> >>
> >> But could vb2_dma_sg_alloc_compacted() be modified so that is uses
> >> dma_alloc_attrs() instead of alloc_pages()? Sorry, that might be a stupid
> >> question, I'm not an expert in this area. All I know is that I hate inconsistent
> >> APIs where something works for one thing, but not another.
> >>
> >
> > dma_alloc_attrs() would allocate contiguous memory, which kind of goes
> > against the vb2_dma_sg allocator idea. Technically we could call it N
> > times with size = 1 page to achieve what we want, but is this really
> > what we want?
> >
> > Given that vb2_dma_sg has always been returning non-consistent memory,
> > do we have any good reason to add consistent memory to it? If so,
> > perhaps we could still do that in an incremental patch, to avoid
> > complicating this already complex series? :)
>
> I very much agree with that. But this should be very clearly documented.
> Should V4L2_CAP_MEMORY_NON_CONSISTENT always be set in this case?
>
Yes, IMHO that would make sense. My understanding is that currently
the consistency of allocated memory is unspecified, so it can be
either. With V4L2_FLAG_MEMORY_NON_CONSISTENT, the userspace can
explicitly ask for inconsistent memory.
Moreover, I'd vote for setting V4L2_CAP_MEMORY_NON_CONSISTENT when
V4L2_FLAG_MEMORY_NON_CONSISTENT is guaranteed to return inconsistent
memory to avoid "optional" features or "hints" without guaranteed
behavior.
> Regards,
>
> Hans
>
> >
> > Best regards,
> > Tomasz
> >
> >> Regards,
> >>
> >> Hans
> >>
> >>>
> >>>> I suspect it was just laziness in the past, and that it should be wired
> >>>> up, just as for dma-contig.
> >>>>
> >>>> Regards,
> >>>>
> >>>> Hans
> >>>>
> >>>>> +static int vb2_dma_sg_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
> >>>>> + enum dma_data_direction direction)
> >>>>> +{
> >>>>> + struct vb2_dma_sg_buf *buf = dbuf->priv;
> >>>>> + struct sg_table *sgt = buf->dma_sgt;
> >>>>> +
> >>>>> + dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> >>>>> + return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int vb2_dma_sg_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
> >>>>> + enum dma_data_direction direction)
> >>>>> +{
> >>>>> + struct vb2_dma_sg_buf *buf = dbuf->priv;
> >>>>> + struct sg_table *sgt = buf->dma_sgt;
> >>>>> +
> >>>>> + dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
> >>>>> + return 0;
> >>>>> +}
> >>>>> +
> >>>>> static void *vb2_dma_sg_dmabuf_ops_vmap(struct dma_buf *dbuf)
> >>>>> {
> >>>>> struct vb2_dma_sg_buf *buf = dbuf->priv;
> >>>>> @@ -488,6 +508,8 @@ static const struct dma_buf_ops vb2_dma_sg_dmabuf_ops = {
> >>>>> .detach = vb2_dma_sg_dmabuf_ops_detach,
> >>>>> .map_dma_buf = vb2_dma_sg_dmabuf_ops_map,
> >>>>> .unmap_dma_buf = vb2_dma_sg_dmabuf_ops_unmap,
> >>>>> + .begin_cpu_access = vb2_dma_sg_dmabuf_ops_begin_cpu_access,
> >>>>> + .end_cpu_access = vb2_dma_sg_dmabuf_ops_end_cpu_access,
> >>>>> .vmap = vb2_dma_sg_dmabuf_ops_vmap,
> >>>>> .mmap = vb2_dma_sg_dmabuf_ops_mmap,
> >>>>> .release = vb2_dma_sg_dmabuf_ops_release,
> >>>>>
> >>>>
> >>
>
next prev parent reply other threads:[~2020-02-03 10:04 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-17 3:20 [RFC][PATCH 00/15] Implement V4L2_BUF_FLAG_NO_CACHE_* flags Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 01/15] videobuf2: add cache management members Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 02/15] videobuf2: handle V4L2 buffer cache flags Sergey Senozhatsky
2020-01-10 10:24 ` Hans Verkuil
2020-01-22 1:39 ` Sergey Senozhatsky
2020-01-22 2:53 ` Sergey Senozhatsky
2020-01-28 4:35 ` Tomasz Figa
2019-12-17 3:20 ` [RFC][PATCH 03/15] videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag Sergey Senozhatsky
2020-01-10 9:36 ` Hans Verkuil
2020-01-10 9:46 ` Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 04/15] videobuf2: add queue memory consistency parameter Sergey Senozhatsky
2020-01-10 9:47 ` Hans Verkuil
2020-01-22 2:05 ` Sergey Senozhatsky
2020-01-23 11:02 ` Hans Verkuil
2020-01-24 2:04 ` Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 05/15] videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT in REQBUFS Sergey Senozhatsky
2020-01-10 9:55 ` Hans Verkuil
2020-01-22 2:18 ` Sergey Senozhatsky
2020-01-22 3:48 ` Sergey Senozhatsky
2020-01-23 11:08 ` Hans Verkuil
2020-01-28 4:45 ` Tomasz Figa
2020-01-28 8:38 ` Hans Verkuil
2019-12-17 3:20 ` [RFC][PATCH 06/15] videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT in CREATE_BUFS Sergey Senozhatsky
2020-01-10 9:59 ` Hans Verkuil
2020-01-23 3:41 ` Sergey Senozhatsky
2020-01-23 11:41 ` Hans Verkuil
2020-01-24 1:28 ` Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 07/15] videobuf2: factor out planes prepare/finish functions Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 08/15] videobuf2: do not sync caches when we are allowed not to Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 09/15] videobuf2: check ->synced flag in prepare() and finish() Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 10/15] videobuf2: let user-space know when driver supports cache hints Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 11/15] videobuf2: add begin/end cpu_access callbacks to dma-contig Sergey Senozhatsky
2019-12-17 3:20 ` [RFC][PATCH 12/15] videobuf2: add begin/end cpu_access callbacks to dma-sg Sergey Senozhatsky
2020-01-10 10:13 ` Hans Verkuil
2020-01-22 6:37 ` Sergey Senozhatsky
2020-01-28 4:38 ` Tomasz Figa
2020-01-28 8:36 ` Hans Verkuil
2020-01-30 11:02 ` Tomasz Figa
2020-01-30 12:18 ` Hans Verkuil
2020-02-03 10:04 ` Tomasz Figa [this message]
2020-02-04 2:50 ` Sergey Senozhatsky
2020-02-06 8:51 ` Tomasz Figa
2019-12-17 3:20 ` [RFC][PATCH 13/15] videobuf2: do not sync buffers for DMABUF queues Sergey Senozhatsky
2020-01-10 10:30 ` Hans Verkuil
2020-01-22 5:05 ` Sergey Senozhatsky
2020-01-23 11:35 ` Hans Verkuil
2020-01-24 2:25 ` Sergey Senozhatsky
2020-01-24 7:32 ` Sergey Senozhatsky
2020-01-28 7:22 ` Tomasz Figa
2020-01-28 7:34 ` Sergey Senozhatsky
2020-01-28 7:19 ` Tomasz Figa
2020-01-28 8:47 ` Hans Verkuil
2019-12-17 3:20 ` [RFC][PATCH 14/15] videobuf2: don't test db_attach in dma-contig prepare and finish Sergey Senozhatsky
2020-01-10 10:32 ` Hans Verkuil
2019-12-17 3:20 ` [RFC][PATCH 15/15] videobuf2: don't test db_attach in dma-sg " Sergey Senozhatsky
2020-01-08 2:27 ` [RFC][PATCH 00/15] Implement V4L2_BUF_FLAG_NO_CACHE_* flags Sergey Senozhatsky
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