RE: [PATCH v2 2/2] media: nxp: imx8-isi: Prioritize pending buffers over discard buffers

[G.N. Zhou (OSS)]

Hi Laurent,

Thanks for your review.

> -----Original Message-----
> From: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Sent: Friday, March 20, 2026 5:59 AM
> To: G.N. Zhou (OSS) <guoniu.zhou@xxxxxxxxxxx>
> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>; Frank Li
> <frank.li@xxxxxxx>; Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>; Pengutronix
> Kernel Team <kernel@xxxxxxxxxxxxxx>; Fabio Estevam
> <festevam@xxxxxxxxx>; Stefan Riedmüller <s.riedmueller@xxxxxxxxx>;
> Jacopo Mondi <jacopo@xxxxxxxxxx>; c.hemp@xxxxxxxxx; linux-
> media@xxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Alexi Birlinger
> <alexi.birlinger@xxxxxxx>; Aisheng Dong <aisheng.dong@xxxxxxx>; G.N.
> Zhou <guoniu.zhou@xxxxxxx>
> Subject: Re: [PATCH v2 2/2] media: nxp: imx8-isi: Prioritize pending buffers over
> discard buffers
> 
> Hi Guoniu,
> 
> Thank you for the patch.
> 
> On Thu, Mar 12, 2026 at 11:12:35AM +0800, Guoniu Zhou wrote:
> > From: Guoniu Zhou <guoniu.zhou@xxxxxxx>
> >
> > Change the buffer selection logic to use pending buffers first (up to
> > the number available), and only use discard buffers to fill remaining
> > slots when insufficient pending buffers are queued. Ensure user
> > buffers are utilized as soon as possible, improving efficiency and
> > reducing the number of discarded frames at stream start.
> 
> The commit message should explain *why* the change is good. How does this
> improve the behaviour ?

Will add the info in next version.

> 
> I'll queue 1/2 in my tree already.
> 
> > Signed-off-by: Guoniu Zhou <guoniu.zhou@xxxxxxx>
> > ---
> > Changes in v2:
> > - Replace "This ensures" with "ensure"
> > - Put example from commit message to comment in driver suggested by Frank
> >
> > https://lore.kernel.org/linux-media/20260311-isi_min_buffers-v1-0-c929
> > 9d6e8ae6@xxxxxxx/T/#m2774912ed31553ef1fdcc840bd6eae53a03ecccd
> > ---
> >  drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > index
> >
> 1be3a728f32f89338a75ddcc4e96e7501ed954e1..77ebff03323ace50ff039c833
> 3d2
> > 5a9c3dd44880 100644
> > --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > @@ -792,7 +792,14 @@ static void
> mxc_isi_video_queue_first_buffers(struct mxc_isi_video *video)
> >  		struct mxc_isi_buffer *buf;
> >  		struct list_head *list;
> >
> > -		list = i < discard ? &video->out_discard : &video->out_pending;
> > +		/*
> > +		 * Queue buffers: prioritize pending buffers, then discard
> buffers
> > +		 * For example:
> > +		 * - 2 pending buffers: both slots use pending buffers
> > +		 * - 1 pending buffer: first slot uses pending, second uses
> discard
> > +		 * - 0 pending buffers: both slots use discard buffers
> > +		 */
> > +		list = (i < 2 - discard) ? &video->out_pending :
> > +&video->out_discard;
> >  		buf = list_first_entry(list, struct mxc_isi_buffer, list);
> >
> >  		mxc_isi_channel_set_outbuf(video->pipe, buf->dma_addrs,
> buf_id);
> >
> 
> --
> Regards,
> 
> Laurent Pinchart