Re: [PATCH v2 3/6] media: nxp: imx8-isi: Fix per-stream reference counting for multiplexed streams

[Frank Li]

On Mon, Jul 20, 2026 at 11:34:05AM +0800, Guoniu Zhou wrote:
> The ISI crossbar fails to properly enable multiple streams from different
> virtual channels on the same input pad. Only the first stream gets enabled
> in hardware, subsequent streams are silently ignored.
>
> The driver uses a single enable_count per input to track the input state.
> When enable_count is non-zero, the code assumes the input is already active
> and skips calling v4l2_subdev_enable_streams() for additional streams:
>
>   Call 1: enable_streams(stream 0)
>     -> enable_count == 0, enable gasket and stream 0 in hardware
>     -> enable_count = 1
>
>   Call 2: enable_streams(stream 1)
>     -> enable_count == 1, skip hardware enable (BUG!)
>     -> enable_count = 2
>     -> stream 1 never gets enabled
>
> Similarly on disable, when enable_count reaches zero, ALL streams are
> disabled regardless of which streams are actually still active.
>
> Fix this by tracking per-stream state using:
> - enabled_streams (u64 bitmask): tracks which streams are currently enabled
> - enabled_count[] (array): per-stream reference counter to support the same
>   stream being enabled/disabled multiple times
>
> Now each stream is independently enabled/disabled in hardware based on the
> enabled_streams bitmask, while enabled_count[] provides reference counting
> for scenarios where the same stream is enabled multiple times, such as
> duplicate cases in the ISI stream.
>
> Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Guoniu Zhou <guoniu.zhou@xxxxxxxxxxx>
> ---
> Changes in v2:
> - Use fixed-size array for enabled_count instead of dynamic allocation
> - Use BIT_ULL() macro for u64 bitmask operations
> - Use MXC_ISI_MAX_STREAMS (64) as loop boundary instead of num_sources
> - Remove mxc_isi_stream_counters_alloc/free functions
> ---
>  .../media/platform/nxp/imx8-isi/imx8-isi-core.h    |  7 +-
>  .../platform/nxp/imx8-isi/imx8-isi-crossbar.c      | 76 ++++++++++++++++------
>  2 files changed, 63 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h b/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> index 7547a6559d4c..9adbe2fe7cf8 100644
> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> @@ -184,8 +184,13 @@ struct mxc_isi_dma_buffer {
>  	dma_addr_t			dma;
>  };
>
> +/* V4L2 subdev max stream ID is 63, need 64 counters (0-63) */
> +#define MXC_ISI_MAX_STREAMS		64

Any existing Macro define max stream ID as 63? it'd better to use such
macro

> +
>  struct mxc_isi_input {
> -	unsigned int			enable_count;
> +	u64				enabled_streams;
> +	/* Per-stream reference counter */
> +	unsigned int			enabled_count[MXC_ISI_MAX_STREAMS];
>  };
>
...
> @@ -396,19 +417,36 @@ static int mxc_isi_crossbar_disable_streams(struct v4l2_subdev *sd,
>
>  	input = &xbar->inputs[sink_pad];
>
> -	input->enable_count--;
> +	/*
> +	 * Decrease the enable count for each stream. Only disable streams
> +	 * whose count reaches zero.
> +	 */
> +	for (stream = 0; stream < MXC_ISI_MAX_STREAMS; stream++) {
> +		if (!(sink_streams & BIT_ULL(stream)))
> +			continue;

for_each_set_bit() ?

Frank
>
> -	if (!input->enable_count) {
> -		ret = v4l2_subdev_disable_streams(remote_sd, remote_pad,
> -						  sink_streams);
> -		if (ret)
> -			dev_err(xbar->isi->dev,
> -				"failed to disable streams 0x%llx on '%s':%u: %d\n",
> -				sink_streams, remote_sd->name, remote_pad, ret);
> +		if (!(input->enabled_streams & BIT_ULL(stream)))
> +			continue;
>
> -		mxc_isi_crossbar_gasket_disable(xbar, sink_pad);
> +		if (--input->enabled_count[stream] == 0)
> +			streams_to_disable |= BIT_ULL(stream);
>  	}
>
> +	if (!streams_to_disable)
> +		return 0;
> +
> +	ret = v4l2_subdev_disable_streams(remote_sd, remote_pad,
> +					  streams_to_disable);
> +	if (ret)
> +		dev_err(xbar->isi->dev,
> +			"failed to disable streams 0x%llx on '%s':%u: %d\n",
> +			streams_to_disable, remote_sd->name, remote_pad, ret);
> +
> +	input->enabled_streams &= ~streams_to_disable;
> +
> +	if (!input->enabled_streams)
> +		mxc_isi_crossbar_gasket_disable(xbar, sink_pad);
> +
>  	return ret;
>  }
>
>
> --
> 2.34.1
>
>