Re: [PATCH 5/8] media: qcom: camss: Fix CSID-to-VFE all-to-all link crossbar on sm8250

[Bryan O'Donoghue <bryan.odonoghue@linaro.org>]

On 11/09/2026 07:22, 
Gjorgji.Rosikopulos.gjorgji.rosikopulos@oss.qualcomm.com wrote:
> From: Gjorgji Rosikopulos <gjorgji.rosikopulos@oss.qualcomm.com>
> 
> camss_link_entities() unconditionally links every CSID to every VFE,
> creating an all-to-all crossbar. On SM8250 the hardware wiring is
> fixed: each CSID is hardwired to exactly one VFE (csid[i] <-> vfe[i]),
> with no crossbar between instances. Enabling a mismatched link (e.g.
> csid0 -> vfe1) creates a media link that does not correspond to any
> real hardware datapath.
> 
> Add a csid_vfe_fixed_pairing flag to struct camss_resources and set it
> for sm8250_resources. When set, camss_link_entities() skips creating
> links between CSID and VFE instances whose indices do not match.
> Other platforms keep the historical all-to-all link creation.
> 
> Signed-off-by: Gjorgji Rosikopulos <gjorgji.rosikopulos@oss.qualcomm.com>
> ---
>   drivers/media/platform/qcom/camss/camss.c | 7 ++++++-
>   drivers/media/platform/qcom/camss/camss.h | 7 +++++++
>   2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> index 2123f6388e3d..1bb22cd23c5e 100644
> --- a/drivers/media/platform/qcom/camss/camss.c
> +++ b/drivers/media/platform/qcom/camss/camss.c
> @@ -5000,7 +5000,10 @@ static int camss_link_entities(struct camss *camss)
>   				}
>   	} else {
>   		for (i = 0; i < camss->res->csid_num; i++)
> -			for (k = 0; k < camss->res->vfe_num; k++)
> +			for (k = 0; k < camss->res->vfe_num; k++) {
> +				if (camss->res->csid_vfe_fixed_pairing && i != k)
> +					continue;
> +

A) This should be a Fixes
B) This should not be limited to sm8250

>   				for (j = 0; j < camss->vfe[k].res->line_num; j++) {
>   					struct v4l2_subdev *csid = &camss->csid[i].subdev;
>   					struct v4l2_subdev *vfe = &camss->vfe[k].line[j].subdev;
> @@ -5017,6 +5020,7 @@ static int camss_link_entities(struct camss *camss)
>   						return ret;
>   					}
>   				}
> +			}
>   	}
>   
>   	return 0;
> @@ -5666,6 +5670,7 @@ static const struct camss_resources sm8250_resources = {
>   	.csiphy_num = ARRAY_SIZE(csiphy_res_8250),
>   	.csid_num = ARRAY_SIZE(csid_res_8250),
>   	.vfe_num = ARRAY_SIZE(vfe_res_8250),
> +	.csid_vfe_fixed_pairing = true,
>   };
>   
>   static const struct camss_resources sc8280xp_resources = {
> diff --git a/drivers/media/platform/qcom/camss/camss.h b/drivers/media/platform/qcom/camss/camss.h
> index 93d691c8ac63..ad0b42719788 100644
> --- a/drivers/media/platform/qcom/camss/camss.h
> +++ b/drivers/media/platform/qcom/camss/camss.h
> @@ -119,6 +119,13 @@ struct camss_resources {
>   	const unsigned int tpg_num;
>   	const unsigned int csid_num;
>   	const unsigned int vfe_num;
> +	/*
> +	 * True on platforms where each CSID is wired to exactly one VFE at
> +	 * the same index (csid[i] <-> vfe[i]). When set, camss_link_entities()
> +	 * only creates CSID->VFE links for matching indices instead of an
> +	 * all-to-all crossbar.
> +	 */
> +	const bool csid_vfe_fixed_pairing;

I think the number of platforms where all-to-all is possible is quite 
low - if possible on any.


>   };
>   
>   struct camss {