linux-kernel - Re: [RFC][PATCH 02/15] videobuf2: handle V4L2 buffer cache flags

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Date:   Tue, 28 Jan 2020 13:35:49 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Hans Verkuil <hans.verkuil@...co.com>,
        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 Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 02/15] videobuf2: handle V4L2 buffer cache flags

On Wed, Jan 22, 2020 at 11:53 AM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (20/01/22 10:39), Sergey Senozhatsky wrote:
> > [..]
> > > >  }
> > > >
> > > > +static void set_buffer_cache_hints(struct vb2_queue *q,
> > > > +                            struct vb2_buffer *vb,
> > > > +                            struct v4l2_buffer *b)
> > > > +{
> > > > + vb->need_cache_sync_on_prepare = 1;
> > > > +
> > > > + if (q->dma_dir != DMA_TO_DEVICE)
> > >
> > > What should be done when dma_dir == DMA_BIDIRECTIONAL?
> >
>
> [..]
>
> > We probably cannot enforce any other behavior here. Am I missing
> > something?
>
> Never mind. I got your point.

DMA_BIDIRECTIONAL by default needs sync on both prepare and finish.
need_cache_sync_on_prepare is initialized to 1. Since
DMA_BIDIRECTIONAL != DMA_TO_DEVICE, need_cache_sync_on_finish would
also be set to 1. Is anything still missing?