linux-kernel - Re: [RFC][PATCH 04/15] videobuf2: add queue memory consistency parameter

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Date:   Fri, 24 Jan 2020 11:04:00 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Sakari Ailus <sakari.ailus@....fi>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pawel Osciak <posciak@...omium.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 04/15] videobuf2: add queue memory consistency
 parameter

On (20/01/23 12:02), Hans Verkuil wrote:
> On 1/22/20 3:05 AM, Sergey Senozhatsky wrote:
> > On (20/01/10 10:47), Hans Verkuil wrote:
> >> On 12/17/19 4:20 AM, Sergey Senozhatsky wrote:
> >>> Preparations for future V4L2_FLAG_MEMORY_NON_CONSISTENT support.
> >>>
> >>> Extend vb2_core_reqbufs() with queue memory consistency flag.
> >>> API permits queue's consistency attribute adjustment only if
> >>> the queue has no allocated buffers, not busy, and does not have
> >>> buffers waiting to be de-queued.
> >>
> >> Actually, you can call vb2_core_reqbufs() when buffers are allocated:
> >> it will free the old buffers, then allocate the new ones.
> >> So drop the 'has no allocated buffers' bit.
> > 
> > Well, the wording, basically, follows the existing vb2_core_reqbufs()
> > behavior "queue memory type"-wise. What I'm trying to say:
> 
> How about this commit log replacement of the first paragraph:
> 
> "Extend vb2_core_reqbufs() with queue memory consistency flag that is
> applied to the newly allocated buffers."

Looks good.

> The bits about 'only if the queue has no allocated buffers, not busy, and does
> not have buffers waiting to be de-queued.' is really irrelevant and confusing
> (at least to me!).

Agreed, those bits describe implementation details which can change.
Better get rid of them.

	-ss