From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Hans Verkuil <hans.verkuil@cisco.com>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Tomasz Figa <tfiga@chromium.org>,
linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv5 00/13] Implement V4L2_BUF_FLAG_NO_CACHE_* flags
Date: Fri, 15 May 2020 00:36:13 +0900 [thread overview]
Message-ID: <20200514153613.GA523@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <aa246282-ca02-a20b-8d8e-0c33f4a2259d@xs4all.nl>
On (20/04/28 16:47), Hans Verkuil wrote:
> Hi Sergey,
>
> On 24/04/2020 11:29, Sergey Senozhatsky wrote:
[..]
> I missed that. What should happen is that q->allow_cache_hints is set by the
> driver before vb2_queue_init is called. And the documentation should be updated
> to say that the V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS flag is only valid when using the
> MMAP streaming I/O model.
>
> Perhaps the flag should be renamed to V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS to
> make this explicit? Other opinions are welcome.
>
> >
> > Second. Even if the queue is setup, we still can report wrong cache
> > hint values. Let's look at the following code
> >
> > fill_buf_caps(q, &p->capabilities);
> > if (!vb2_queue_allows_cache_hints(q))
> > p->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT;
>
> The problem here is that vb2_queue_allows_cache_hints(q) uses stale information:
> the current streaming mode instead of the requested streaming mode.
>
> This should read:
>
> if (!q->allow_cache_hints || p->memory != V4L2_MEMORY_MMAP)
> p->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT;
>
> And V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS is always set regardless of the
> memory model. It just needs to be documented that this capability applies
> to MMAP mode only.
>
> > ret = vb2_core_reqbufs(...);
> > return ret;
> >
> > The thing here is that vb2_core_reqbufs() and vb2_core_create_bufs()
> > can re-initialize the queue and invoke ->queue_setup(), possibly
> > changing its memory model, etc. so cache hints cap which we set or
> > clear before vb2_core_reqbufs() and vb2_core_create_bufs() can become
> > invalid after we call those functions. It's the same with
> > ``req->flags &= ~V4L2_FLAG_MEMORY_NON_CONSISTENT``, we cannot clear
> > it before reqbufs()/create_bufs(). Therefore I added two simple
> > functions which fixup cache hint cap and non_consistent flag after
> > reqbufs()/create_bufs(). So the code looks like this now:
> >
> > fill_buf_caps(q, &p->capabilities);
> > ret = vb2_core_reqbufs(...);
> > fixup_consistency_attr(q, &p->flags);
> > fixup_cache_hints_cap(q, &p->capabilities);
>
> These fixup functions are ugly, unless I missed something I think the
> approach described above works just fine.
>
> With these changes I think it is ready to go in.
ACK to all of these.
Will send the updated patch set shortly.
-ss
prev parent reply other threads:[~2020-05-14 15:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-24 9:29 [PATCHv5 00/13] Implement V4L2_BUF_FLAG_NO_CACHE_* flags Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 01/13] videobuf2: use explicit unsigned int in vb2_queue Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 02/13] videobuf2: add cache management members Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 03/13] videobuf2: handle V4L2 buffer cache flags Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 04/13] videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 05/13] videobuf2: add queue memory consistency parameter Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 06/13] videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT flag Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 07/13] videobuf2: factor out planes prepare/finish functions Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 08/13] videobuf2: do not sync caches when we are allowed not to Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 09/13] videobuf2: check ->synced flag in prepare() and finish() Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 10/13] videobuf2: add begin/end cpu_access callbacks to dma-contig Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 11/13] videobuf2: add begin/end cpu_access callbacks to dma-sg Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 12/13] videobuf2: don't test db_attach in dma-contig prepare and finish Sergey Senozhatsky
2020-04-24 9:29 ` [PATCHv5 13/13] media: vivid: add cache_hints module param Sergey Senozhatsky
2020-04-28 14:47 ` [PATCHv5 00/13] Implement V4L2_BUF_FLAG_NO_CACHE_* flags Hans Verkuil
2020-05-14 15:36 ` Sergey Senozhatsky [this message]
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