[PATCH v6 2/3] drm/i915/gt: Do not generate the command streamer for all the CCS

[Matt Roper]

On Wed, Mar 13, 2024 at 09:19:50PM +0100, Andi Shyti wrote:
> We want a fixed load CCS balancing consisting in all slices
> sharing one single user engine. For this reason do not create the
> intel_engine_cs structure with its dedicated command streamer for
> CCS slices beyond the first.
> 
> Fixes: d2eae8e98d59 ("drm/i915/dg2: Drop force_probe requirement")
> Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
> Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Matt Roper <matthew.d.roper at intel.com>
> Cc: <stable at vger.kernel.org> # v6.2+
> ---
>  drivers/gpu/drm/i915/gt/intel_engine_cs.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index f553cf4e6449..c4fb31bb6e72 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -966,6 +966,7 @@ int intel_engines_init_mmio(struct intel_gt *gt)
>  	const unsigned int engine_mask = init_engine_mask(gt);
>  	unsigned int mask = 0;
>  	unsigned int i, class;
> +	u8 ccs_instance = 0;
>  	u8 logical_ids[MAX_ENGINE_INSTANCE + 1];
>  	int err;
>  
> @@ -986,6 +987,19 @@ int intel_engines_init_mmio(struct intel_gt *gt)
>  			    !HAS_ENGINE(gt, i))
>  				continue;
>  
> +			/*
> +			 * Do not create the command streamer for CCS slices
> +			 * beyond the first. All the workload submitted to the
> +			 * first engine will be shared among all the slices.
> +			 *
> +			 * Once the user will be allowed to customize the CCS
> +			 * mode, then this check needs to be removed.
> +			 */
> +			if (IS_DG2(i915) &&
> +			    class == COMPUTE_CLASS &&
> +			    ccs_instance++)
> +				continue;

Wouldn't it be more intuitive to drop the non-lowest CCS engines in
init_engine_mask() since that's the function that's dedicated to
building the list of engines we'll use?  Then we don't need to kill the
assertion farther down either.


Matt

> +
>  			err = intel_engine_setup(gt, i,
>  						 logical_ids[instance]);
>  			if (err)
> @@ -996,11 +1010,9 @@ int intel_engines_init_mmio(struct intel_gt *gt)
>  	}
>  
>  	/*
> -	 * Catch failures to update intel_engines table when the new engines
> -	 * are added to the driver by a warning and disabling the forgotten
> -	 * engines.
> +	 * Update the intel_engines table.
>  	 */
> -	if (drm_WARN_ON(&i915->drm, mask != engine_mask))
> +	if (mask != engine_mask)
>  		gt->info.engine_mask = mask;
>  
>  	gt->info.num_engines = hweight32(mask);
> -- 
> 2.43.0
> 

-- 
Matt Roper
Graphics Software Engineer
Linux GPU Platform Enablement
Intel Corporation