[PATCH 1/3] drm/amd/display: Fix refactored DSC cap calculation

[Rodrigo Siqueira]

On 010/22, Timur Kristóf wrote:
> After refactoring the DSC capability calculation, the
> get_min_slice_count_for_odm could crash on some GPUs due to a
> division by zero when max_total_throughput_mps was zero.
> As a result, DC was broken when connecting a GPU that doesn't
> support DSC to a monitor that supports DSC.
> Tested on Oland (DCE 6) and Fiji (DCE 10).
> 
> This commit fixes it by returning zero instead.
> 
> Fixes: 4909b8b3846c ("drm/amd/display: Refactor DSC cap calculations")
> Signed-off-by: Timur Kristóf <timur.kristof at gmail.com>
> ---
>  drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
> index a454d16e6586..4169ece9c535 100644
> --- a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
> +++ b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
> @@ -642,14 +642,15 @@ static unsigned int get_min_slice_count_for_odm(
>  	unsigned int max_dispclk_khz;
>  
>  	/* get max pixel rate and combine caps */
> -	max_dispclk_khz = dsc_enc_caps->max_total_throughput_mps * 1000;
> -	if (dsc && dsc->ctx->dc) {
> -		if (dsc->ctx->dc->clk_mgr &&
> -			dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz) {
> -			/* dispclk is available */
> -			max_dispclk_khz = dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz(dsc->ctx->dc->clk_mgr, CLK_TYPE_DISPCLK);
> -		}
> -	}
> +	if (dsc && dsc->ctx->dc && dsc->ctx->dc->clk_mgr &&
> +		dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz)
> +		max_dispclk_khz =
> +			dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz(
> +				dsc->ctx->dc->clk_mgr, CLK_TYPE_DISPCLK);
> +	else if (dsc_enc_caps->max_total_throughput_mps)
> +		max_dispclk_khz = dsc_enc_caps->max_total_throughput_mps * 1000;
> +	else
> +		return 0;
>  
>  	/* consider minimum odm slices required due to
>  	 * 1) display pipe throughput (dispclk)
> -- 
> 2.50.1
>

This patch lgtm.

Reviewed-by: Rodrigo Siqueira <siqueira at igalia.com>

I added other display folks to this patch.

I'm not sure if the original modification (4909b8b3846c) is already in
the stable kernel; if so, it could be a good idea to send this fix to
the stable kernel as well.

Thanks

-- 
Rodrigo Siqueira