Re: [PATCH] drm/amd/display: Fix surface optimization regression on Carrizo

[Harry Wentland <harry.wentland@amd.com>]

On 2021-10-12 10:11, Nicholas Kazlauskas wrote:
> [Why]
> DCE legacy optimization path isn't well tested under new DC optimization
> flow which can result in underflow occuring when initializing X11 on
> Carrizo.
> 
> [How]
> Retain the legacy optimization flow for DCE and keep the new one for DCN
> to satisfy optimizations being correctly applied for ASIC that can
> support it.
> 
> Fixes: ab37c6527bb1 ("drm/amd/display: Optimize bandwidth on following fast update")
> Cc: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
> Cc: Mikita Lipski <mikita.lipski@amd.com>
> Reported-by: Tom St Denis <tom.stdenis@amd.com>
> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>

Reviewed-by: Harry Wentland <harry.wentland@amd.com>

Harry

> ---
>  drivers/gpu/drm/amd/display/dc/core/dc.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc.c b/drivers/gpu/drm/amd/display/dc/core/dc.c
> index da942e9f5142..f9876e429f26 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc.c
> @@ -3118,8 +3118,13 @@ void dc_commit_updates_for_stream(struct dc *dc,
>  			if (new_pipe->plane_state && new_pipe->plane_state != old_pipe->plane_state)
>  				new_pipe->plane_state->force_full_update = true;
>  		}
> -	} else if (update_type == UPDATE_TYPE_FAST) {
> -		/* Previous frame finished and HW is ready for optimization. */
> +	} else if (update_type == UPDATE_TYPE_FAST && dc_ctx->dce_version >= DCE_VERSION_MAX) {
> +		/*
> +		 * Previous frame finished and HW is ready for optimization.
> +		 *
> +		 * Only relevant for DCN behavior where we can guarantee the optimization
> +		 * is safe to apply - retain the legacy behavior for DCE.
> +		 */
>  		dc_post_update_surfaces_to_stream(dc);
>  	}
>  
> @@ -3178,6 +3183,12 @@ void dc_commit_updates_for_stream(struct dc *dc,
>  		}
>  	}
>  
> +	/* Legacy optimization path for DCE. */
> +	if (update_type >= UPDATE_TYPE_FULL && dc_ctx->dce_version < DCE_VERSION_MAX) {
> +		dc_post_update_surfaces_to_stream(dc);
> +		TRACE_DCE_CLOCK_STATE(&context->bw_ctx.bw.dce);
> +	}
> +
>  	return;
>  
>  }
>