Re: [Intel-gfx] [PATCH V2] drm/i915/gt: Add workaround 14016712196

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 17.05.2023 15:22, Tejas Upadhyay wrote:
> Wa_14016712196 implementation for mtl
> 
> Bspec: 72197
> 
> V2:
>    - Fix  kernel test robot warnings
> 
> Reported-by: kernel test robot <lkp@intel.com>

I do not think robot reported lack of this wa :), putting lkp in 
changelog should be enough.


> Closes: https://lore.kernel.org/oe-kbuild-all/202305121525.3EWdGoBY-lkp@intel.com/
> Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/gen8_engine_cs.c | 41 ++++++++++++++++++++++++
>   1 file changed, 41 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> index e1c76e5bfa82..737eb515544b 100644
> --- a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
> @@ -177,14 +177,38 @@ u32 *gen12_emit_aux_table_inv(struct intel_gt *gt, u32 *cs, const i915_reg_t inv
>   	return cs;
>   }
>   
> +static int mtl_dummy_pipe_control(struct i915_request *rq, u32 *cs)
> +{
> +	if (IS_ERR(cs))
> +		return PTR_ERR(cs);
> +	cs = gen12_emit_pipe_control(cs,
> +				     0,
> +				     PIPE_CONTROL_DEPTH_CACHE_FLUSH,
> +				     LRC_PPHWSP_SCRATCH_ADDR);
> +	intel_ring_advance(rq, cs);
> +
> +	return 0;
> +}
> +
>   int gen12_emit_flush_rcs(struct i915_request *rq, u32 mode)
>   {
>   	struct intel_engine_cs *engine = rq->engine;
> +	int err;
>   
>   	if (mode & EMIT_FLUSH) {
>   		u32 flags = 0;
>   		u32 *cs;
>   
> +		/* Wa_14016712196 */
> +		if (IS_MTL_GRAPHICS_STEP(engine->i915, M, STEP_A0, STEP_B0) ||
> +		    IS_MTL_GRAPHICS_STEP(engine->i915, P, STEP_A0, STEP_B0)) {
> +			/* dummy PIPE_CONTROL + depth flush */
> +			cs = intel_ring_begin(rq, 6);
> +			err = mtl_dummy_pipe_control(rq, cs);
> +			if (err)
> +				return err;

Like Andi suggested, you can replace above sequence with:
	cs = mtl_dummy_pipe_control(rq);


> +		}
> +
>   		flags |= PIPE_CONTROL_TILE_CACHE_FLUSH;
>   		flags |= PIPE_CONTROL_FLUSH_L3;
>   		flags |= PIPE_CONTROL_RENDER_TARGET_CACHE_FLUSH;
> @@ -218,6 +242,16 @@ int gen12_emit_flush_rcs(struct i915_request *rq, u32 mode)
>   		u32 flags = 0;
>   		u32 *cs, count;
>   
> +		/* Wa_14016712196 */
> +		if (IS_MTL_GRAPHICS_STEP(engine->i915, M, STEP_A0, STEP_B0) ||
> +		    IS_MTL_GRAPHICS_STEP(engine->i915, P, STEP_A0, STEP_B0)) {
> +			/* dummy PIPE_CONTROL + depth flush */
> +			cs = intel_ring_begin(rq, 6);
> +			err = mtl_dummy_pipe_control(rq, cs);
> +			if (err)
> +				return err;
> +		}
> +

In case gen12_emit_flush_rcs is called with EMIT_BARRIER = 
(EMIT_INVALIDATE | EMIT_FLUSH) dummy pipe will be inserted twice, is it OK?

>   		flags |= PIPE_CONTROL_COMMAND_CACHE_INVALIDATE;
>   		flags |= PIPE_CONTROL_TLB_INVALIDATE;
>   		flags |= PIPE_CONTROL_INSTRUCTION_CACHE_INVALIDATE;
> @@ -733,6 +767,13 @@ u32 *gen12_emit_fini_breadcrumb_rcs(struct i915_request *rq, u32 *cs)
>   		     PIPE_CONTROL_DC_FLUSH_ENABLE |
>   		     PIPE_CONTROL_FLUSH_ENABLE);
>   
> +	/* Wa_14016712196 */
> +	if (IS_MTL_GRAPHICS_STEP(i915, M, STEP_A0, STEP_B0) ||
> +	    IS_MTL_GRAPHICS_STEP(i915, P, STEP_A0, STEP_B0))
> +		/* dummy PIPE_CONTROL + depth flush */
> +		cs = gen12_emit_pipe_control(cs, 0,
> +					     PIPE_CONTROL_DEPTH_CACHE_FLUSH, 0);

How do we know there is enough space for dummy pipe?

Regards
Andrzej

> +
>   	if (GRAPHICS_VER(i915) == 12 && GRAPHICS_VER_FULL(i915) < IP_VER(12, 50))
>   		/* Wa_1409600907 */
>   		flags |= PIPE_CONTROL_DEPTH_STALL;