Re: [Intel-gfx] [PATCH 06/10] drm/i915: Add Wa_22011802037 force cs halt

[John Harrison <john.c.harrison@intel.com>]

On 4/13/2022 12:27, Umesh Nerlige Ramappa wrote:
> From: Tilak Tangudu <tilak.tangudu@intel.com>
>
> Prior to doing a reset, SW must ensure command streamer is stopped,
> as a workaround, to eliminate a race condition in GPM flow.
> Setting both the ring stop and prefetch disable bits, will cause the
> command streamer to halt.
>
> v2: 1. Removed duplicate code and added only prefetch disable -Chris Wilson
>
> v3: 1. Applied wa for all gen12+ -Lahtinen Joonas/Vivi Rodrigo
>
> v4: 1. Added description in comment
>      2. Added WA prior to read barrier-Chris Wilson
>
> v5: 1. Modified to disable prefetch and wait for idle ack -Chris Wilson
Is this comment accurate? I'm not seeing a 'wait for idle ack' in the 
deltas. There is a wait for idle function but it is already present and 
not part of this patch change.

>
> Signed-off-by: Tilak Tangudu <tilak.tangudu@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_engine_cs.c   | 9 +++++++++
>   drivers/gpu/drm/i915/gt/intel_engine_regs.h | 1 +
>   2 files changed, 10 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index 98b61ff13c95..14c6ddbbfde8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -1280,6 +1280,15 @@ static int __intel_engine_stop_cs(struct intel_engine_cs *engine,
>   	int err;
>   
>   	intel_uncore_write_fw(uncore, mode, _MASKED_BIT_ENABLE(STOP_RING));
> +
> +	/*
> +	 * Wa_22011802037 : gen12, Prior to doing a reset, ensure CS is
> +	 * stopped, set ring stop bit and prefetch disable bit to halt CS
> +	 */
> +	if (GRAPHICS_VER(engine->i915) == 12)
> +		intel_uncore_write_fw(uncore, RING_MODE_GEN7(engine->mmio_base),
> +				      _MASKED_BIT_ENABLE(GEN12_GFX_PREFETCH_DISABLE));
> +
>   	err = __intel_wait_for_register_fw(engine->uncore, mode,
>   					   MODE_IDLE, MODE_IDLE,
>   					   fast_timeout_us,
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_regs.h b/drivers/gpu/drm/i915/gt/intel_engine_regs.h
> index 0bf8b45c9319..594a629cb28f 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_regs.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_regs.h
> @@ -181,6 +181,7 @@
>   #define   GFX_SURFACE_FAULT_ENABLE		(1 << 12)
>   #define   GFX_REPLAY_MODE			(1 << 11)
>   #define   GFX_PSMI_GRANULARITY			(1 << 10)
> +#define   GEN12_GFX_PREFETCH_DISABLE		REG_BIT(10)
So the PSMI_GRANULARITY bit is not valid for Gen12 onwards? I'm not 
actually seeing it being used anywhere. So I guess it doesn't matte anyway!

Reviewed-by: John Harrison <John.C.Harrison@Intel.com>

>   #define   GFX_PPGTT_ENABLE			(1 << 9)
>   #define   GEN8_GFX_PPGTT_48B			(1 << 7)
>   #define   GFX_FORWARD_VBLANK_MASK		(3 << 5)