linux-kernel - Re: [PATCH v8 11/18] media: ti: j721e-csi2rx: add support for processing virtual channels

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Message-ID: <442f321e-be2e-4a42-ba3e-d8a58eaac11b@ideasonboard.com>
Date: Thu, 20 Nov 2025 14:32:40 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Rishikesh Donadkar <r-donadkar@...com>, jai.luthra@...ux.dev,
 laurent.pinchart@...asonboard.com, mripard@...nel.org
Cc: y-abhilashchandra@...com, devarsht@...com, s-jain1@...com,
 vigneshr@...com, mchehab@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 p.zabel@...gutronix.de, conor+dt@...nel.org, sakari.ailus@...ux.intel.com,
 hverkuil-cisco@...all.nl, jai.luthra@...asonboard.com,
 changhuang.liang@...rfivetech.com, jack.zhu@...rfivetech.com,
 sjoerd@...labora.com, dan.carpenter@...aro.org, hverkuil+cisco@...nel.org,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH v8 11/18] media: ti: j721e-csi2rx: add support for
 processing virtual channels

Hi,

On 12/11/2025 13:54, Rishikesh Donadkar wrote:
> From: Jai Luthra <j-luthra@...com>
> 
> Use get_frame_desc() to get the frame desc from the connected source,
> and use the provided virtual channel instead of hardcoded one.

So this baffled me a bit: the code seems to get the VC from the frame
desc, but not the DT. But it looks like the DT values are hardcoded in
the driver's formats table, and those are used for DT filtering.

We need to do something like that for legacy cases where the source does
not support get_frame_desc, but if there is a frame desc, we should use
the DT and VC from the frame desc.

> get_frame_desc() returns the same information when called on each stream
> start, so instead get the VCs for all the routed stream at first
> stream start and cache this information in the driver.

I get the point but... There isn't anything like this in the patch?

> get_frame_desc() works per stream, but as we don't support multiple

"get_frame_desc() works per stream", what does it mean? It returns all
the streams for a pad.

> streams yet, we will just always use stream 0. If the source doesn't
> support get_frame_desc(), fall back to the previous method of always
> capturing virtual channel 0.

Right, if there's no frame desc (and we need to support legacy drivers),
the driver should default to VC=0, DT from the formats table. But as
mentioned above, VC and DT should normally come from the frame desc. It
would be good to have a separate "legacy" function/branch/something, so
that we clearly distinguish the legacy and frame-desc cases.

 Tomi

> Reviewed-by: Yemike Abhilash Chandra <y-abhilashchandra@...com>
> Co-developed-by: Pratyush Yadav <p.yadav@...com>
> Signed-off-by: Pratyush Yadav <p.yadav@...com>
> Signed-off-by: Jai Luthra <j-luthra@...com>
> Signed-off-by: Rishikesh Donadkar <r-donadkar@...com>
> ---
>  .../platform/ti/j721e-csi2rx/j721e-csi2rx.c   | 38 +++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> index 5c4524bf42e6e..126a62fa2c4c4 100644
> --- a/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> +++ b/drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c
> @@ -32,6 +32,7 @@
>  #define SHIM_DMACNTX_YUV422		GENMASK(27, 26)
>  #define SHIM_DMACNTX_DUAL_PCK_CFG	BIT(24)
>  #define SHIM_DMACNTX_SIZE		GENMASK(21, 20)
> +#define SHIM_DMACNTX_VC			GENMASK(9, 6)
>  #define SHIM_DMACNTX_FMT		GENMASK(5, 0)
>  #define SHIM_DMACNTX_YUV422_MODE_11	3
>  #define SHIM_DMACNTX_SIZE_8		0
> @@ -110,6 +111,8 @@ struct ti_csi2rx_ctx {
>  	struct media_pad		pad;
>  	u32				sequence;
>  	u32				idx;
> +	u32				vc;
> +	u32				stream;
>  };
>  
>  struct ti_csi2rx_dev {
> @@ -610,6 +613,7 @@ static void ti_csi2rx_setup_shim(struct ti_csi2rx_ctx *ctx)
>  	}
>  
>  	reg |= FIELD_PREP(SHIM_DMACNTX_SIZE, fmt->size);
> +	reg |= FIELD_PREP(SHIM_DMACNTX_VC, ctx->vc);
>  
>  	writel(reg, csi->shim + SHIM_DMACNTX(ctx->idx));
>  
> @@ -884,6 +888,32 @@ static void ti_csi2rx_buffer_queue(struct vb2_buffer *vb)
>  	}
>  }
>  
> +static int ti_csi2rx_get_vc(struct ti_csi2rx_ctx *ctx)
> +{
> +	struct ti_csi2rx_dev *csi = ctx->csi;
> +	struct v4l2_mbus_frame_desc fd;
> +	struct media_pad *pad;
> +	int ret, i;
> +
> +	pad = media_entity_remote_pad_unique(&csi->subdev.entity, MEDIA_PAD_FL_SOURCE);
> +	if (!pad)
> +		return -ENODEV;
> +
> +	ret = v4l2_subdev_call(csi->source, pad, get_frame_desc, pad->index, &fd);
> +	if (ret)
> +		return ret;
> +
> +	if (fd.type != V4L2_MBUS_FRAME_DESC_TYPE_CSI2)
> +		return -EINVAL;
> +
> +	for (i = 0; i < fd.num_entries; i++) {
> +		if (ctx->stream == fd.entry[i].stream)
> +			return fd.entry[i].bus.csi2.vc;
> +	}
> +
> +	return -ENODEV;
> +}
> +
>  static int ti_csi2rx_start_streaming(struct vb2_queue *vq, unsigned int count)
>  {
>  	struct ti_csi2rx_ctx *ctx = vb2_get_drv_priv(vq);
> @@ -904,6 +934,14 @@ static int ti_csi2rx_start_streaming(struct vb2_queue *vq, unsigned int count)
>  	if (ret)
>  		goto err;
>  
> +	ret = ti_csi2rx_get_vc(ctx);
> +	if (ret == -ENOIOCTLCMD)
> +		ctx->vc = 0;
> +	else if (ret < 0)
> +		goto err;
> +	else
> +		ctx->vc = ret;
> +
>  	ti_csi2rx_setup_shim(ctx);
>  
>  	ctx->sequence = 0;