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

[Gjorgji Rosikopulos (Consultant)]

Hi Bryan,

Thanks for the review,

On 9/11/2026 2:37 PM, Bryan O'Donoghue wrote:
> On 11/09/2026 07:22, 
> Gjorgji.Rosikopulos.gjorgji.rosikopulos@xxxxxxxxxxxxxxxx wrote:
>> From: Gjorgji Rosikopulos <gjorgji.rosikopulos@xxxxxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxxx>
>> ---
>>   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

I agree. I think either we can have this based on platform, or based on ispif availability.
The csid routing to all ife's is possible only in the platforms with ispif available.
Please tell me what is your preference i am fine with both.

> 
>>   				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.

Yes that is correct.

~Gjorgji