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

[Gupta, Anshuman]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Alan
> Previn
> Sent: Friday, January 20, 2023 1:20 AM
> To: intel-gfx at lists.freedesktop.org
> Cc: Vivi at freedesktop.org; dri-devel at lists.freedesktop.org; Teres Alexis,
> Alan Previn <alan.previn.teres.alexis at intel.com>; Vivi, Rodrigo
> <rodrigo.vivi at intel.com>
> Subject: [Intel-gfx] [PATCH 1/1] drm/i915/gsc: Fix the Driver-FLR completion
> 
> 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 at 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 */
> +	ret = intel_wait_for_register_fw(uncore, GU_CNTL,
> +					 DRIVERFLR_STATUS, 0,
> +					 flr_timeout_ms);
We need an error here if above wait timeout then below wait is essentially a NOP.
And driver may return before completion of FLR.
Thanks,
Anshuman Gupta.
> +
> +	/* Completion: Step 2 - poll for 'DEBUG-BIT31 = 1' for hw/fw 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 */
>  	intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);  }
> 
> 
> base-commit: 0a0ee61784df01ac098a92bd43673ee30c629f13
> --
> 2.39.0