Re: [Intel-gfx] [PATCH 1/1] drm/i915/gsc: Fix the Driver-FLR completion

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 19 Jan 2023, Alan Previn <alan.previn.teres.alexis@intel.com> wrote:
> The Driver-FLR flow may inadvertently exit early before the full
> completion of the re-init of the internal HW state if we only poll
> GU_DEBUG Bit31 (polling for it to toggle from 0 -> 1). Instead
> we need a two-step completion wait-for-completion flow that also
> involves GU_CNTL. See the patch and new code comments for detail.
> This is new direction from HW architecture folks.
>
> Signed-off-by: Alan Previn <alan.previn.teres.alexis@intel.com>
> Fixes: 5a44fcd73498 ("drm/i915/gsc: Do a driver-FLR on unload if GSC was loaded")
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 8dee9e62a73e..959869e2ff05 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -2748,6 +2748,12 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
>  	/* Trigger the actual Driver-FLR */
>  	intel_uncore_rmw_fw(uncore, GU_CNTL, 0, DRIVERFLR);
>  
> +	/* Completion Step 1 - poll for 'CNTL-BIT31 = 0' wait for hw teardown to complete */

Please don't use comments to repeat what the code already says.

Here, you could just say, "Wait for hardware teardown to complete",
which describes what the code does at a higher level, but does not
duplicate any of it.

> +	ret = intel_wait_for_register_fw(uncore, GU_CNTL,
> +					 DRIVERFLR_STATUS, 0,
> +					 flr_timeout_ms);
> +
> +	/* Completion: Step 2 - poll for 'DEBUG-BIT31 = 1' for hw/fw re-init to complete */

"Wait for hardware/firmware re-init to complete"

>  	ret = intel_wait_for_register_fw(uncore, GU_DEBUG,
>  					 DRIVERFLR_STATUS, DRIVERFLR_STATUS,
>  					 flr_timeout_ms);
> @@ -2756,6 +2762,7 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
>  		return;
>  	}
>  
> +	/* Write 1 to clear GU_DEBUG's sticky completion status bit */

"Clear sticky completion status" maybe?

>  	intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);
>  }
>  
>
> base-commit: 0a0ee61784df01ac098a92bd43673ee30c629f13

-- 
Jani Nikula, Intel Open Source Graphics Center