[PATCH v2 0/2] media: nxp: imx8-isi: Fix single frame capture and optimize buffer usage

[PATCH v2 0/2] media: nxp: imx8-isi: Fix single frame capture and optimize buffer usage

[Guoniu Zhou]

This series fixes a hang issue when capturing single frames and improves
buffer utilization by prioritizing user buffers over discard buffers.

Patch 1 reduces min_queued_buffers to allow streaming with a single buffer,
fixing hangs in applications like libcamera's cam tool.

Patch 2 changes the buffer selection logic to use pending user buffers first,
minimizing unnecessary frame drops at stream start.

Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
---
Changes in v2:
- Add fix tag
- Replace "This ensures" with "ensure"
- Reduce min_queued_buffers from 2 to 0 suggested by Jacopo Mondi
- Put example from commit message to comment in driver suggested by Frank
- Detailed changes can be found in each patch's changelog
- Link to v1: https://lore.kernel.org/r/20260311-isi_min_buffers-v1-0-c9299d6e8ae6@nxp.com

---
Guoniu Zhou (2):
      media: nxp: imx8-isi: Reduce minimum queued buffers from 2 to 0
      media: nxp: imx8-isi: Prioritize pending buffers over discard buffers

 drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260310-isi_min_buffers-4b490a124223

Best regards,
-- 
Guoniu Zhou <guoniu.zhou@nxp.com>

[PATCH v2 1/2] media: nxp: imx8-isi: Reduce minimum queued buffers from 2 to 0

[Guoniu Zhou]

From: Guoniu Zhou <guoniu.zhou@nxp.com>

Fix a hang issue when capturing a single frame with applications like cam
in libcamera. It would hang waiting for the driver to complete the buffer,
but streaming never starts because min_queued_buffers was set to 2.

The ISI module uses a ping-pong buffer mechanism that requires two buffers
to be programmed at all times. However, when fewer than 2 user buffers are
available, the driver use internal discard buffers to fill the remaining
slot(s). Reduce minimum queued buffers from 2 to 0 allows streaming to
start without any queued buffers.

Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
Cc: stable@vger.kernel.org
Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
---
Changes in v2:
- Reduce min_queued_buffers from 2 to 0 suggested by Jacopo Mondi
  https://lore.kernel.org/linux-media/20260311-isi_min_buffers-v1-0-c9299d6e8ae6@nxp.com/T/#mcd4b7dcc218a02e2f218ba2c83b947ccefd9308b
- Add fix tag
---
 drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 2 +-
 1 file changed, 1 insertion(+), 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 13682bf6e9f8895bb9eb1f92d5f74b0d5968544e..1be3a728f32f89338a75ddcc4e96e7501ed954e1 100644
--- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
+++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
@@ -1410,7 +1410,7 @@ int mxc_isi_video_register(struct mxc_isi_pipe *pipe,
 	q->mem_ops = &vb2_dma_contig_memops;
 	q->buf_struct_size = sizeof(struct mxc_isi_buffer);
 	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
-	q->min_queued_buffers = 2;
+	q->min_queued_buffers = 0;
 	q->lock = &video->lock;
 	q->dev = pipe->isi->dev;
 

-- 
2.34.1

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

[Guoniu Zhou]

From: Guoniu Zhou <guoniu.zhou@nxp.com>

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.

Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
---
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-c9299d6e8ae6@nxp.com/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..77ebff03323ace50ff039c8333d25a9c3dd44880 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);

-- 
2.34.1

Re: [PATCH v2 1/2] media: nxp: imx8-isi: Reduce minimum queued buffers from 2 to 0

[Laurent Pinchart]

Hi Guoniu,

Thank you for the patch.

On Thu, Mar 12, 2026 at 11:12:34AM +0800, Guoniu Zhou wrote:
> From: Guoniu Zhou <guoniu.zhou@nxp.com>
> 
> Fix a hang issue when capturing a single frame with applications like cam
> in libcamera. It would hang waiting for the driver to complete the buffer,
> but streaming never starts because min_queued_buffers was set to 2.
> 
> The ISI module uses a ping-pong buffer mechanism that requires two buffers
> to be programmed at all times. However, when fewer than 2 user buffers are
> available, the driver use internal discard buffers to fill the remaining
> slot(s). Reduce minimum queued buffers from 2 to 0 allows streaming to
> start without any queued buffers.
> 
> Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
> Cc: stable@vger.kernel.org
> Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
> ---
> Changes in v2:
> - Reduce min_queued_buffers from 2 to 0 suggested by Jacopo Mondi
>   https://lore.kernel.org/linux-media/20260311-isi_min_buffers-v1-0-c9299d6e8ae6@nxp.com/T/#mcd4b7dcc218a02e2f218ba2c83b947ccefd9308b
> - Add fix tag
> ---
>  drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 2 +-
>  1 file changed, 1 insertion(+), 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 13682bf6e9f8895bb9eb1f92d5f74b0d5968544e..1be3a728f32f89338a75ddcc4e96e7501ed954e1 100644
> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> @@ -1410,7 +1410,7 @@ int mxc_isi_video_register(struct mxc_isi_pipe *pipe,
>  	q->mem_ops = &vb2_dma_contig_memops;
>  	q->buf_struct_size = sizeof(struct mxc_isi_buffer);
>  	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> -	q->min_queued_buffers = 2;
> +	q->min_queued_buffers = 0;

A simple way to fix the issue, that's nice.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

>  	q->lock = &video->lock;
>  	q->dev = pipe->isi->dev;
>  
> 

-- 
Regards,

Laurent Pinchart

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

[Laurent Pinchart]

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@nxp.com>
> 
> 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 ?

I'll queue 1/2 in my tree already.

> Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
> ---
> 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-c9299d6e8ae6@nxp.com/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..77ebff03323ace50ff039c8333d25a9c3dd44880 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

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@ideasonboard.com>
> Sent: Friday, March 20, 2026 5:59 AM
> To: G.N. Zhou (OSS) <guoniu.zhou@oss.nxp.com>
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>; Frank Li
> <frank.li@nxp.com>; Sascha Hauer <s.hauer@pengutronix.de>; Pengutronix
> Kernel Team <kernel@pengutronix.de>; Fabio Estevam
> <festevam@gmail.com>; Stefan Riedmüller <s.riedmueller@phytec.de>;
> Jacopo Mondi <jacopo@jmondi.org>; c.hemp@phytec.de; linux-
> media@vger.kernel.org; imx@lists.linux.dev; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; Alexi Birlinger
> <alexi.birlinger@nxp.com>; Aisheng Dong <aisheng.dong@nxp.com>; G.N.
> Zhou <guoniu.zhou@nxp.com>
> 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@nxp.com>
> >
> > 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@nxp.com>
> > ---
> > 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@nxp.com/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