Re: [PATCH 1/5] drm/i915/dsi: Don't do DSC horizontal timing adjustments in command mode

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 26 Mar 2026, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Stop adjusting the horizontal timing values based on the
> compression ratio in command mode. Bspec seems to be telling
> us to do this only in video mode, and this is also how the
> Windows driver does things.
>
> This should also fix a div-by-zero on some machines because due to
> the adjusted htotal ends up being so small that we end up with
> line_time_us==0 when trying to determine the vtotal value in
> command mode.
>
> Note that this doesn't actually make the display on the
> Huawei Matebook E work, but at least the kernel no longer
> explodes when the driver loads.
>
> Cc: stable@vger.kernel.org
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12045
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Fixes: 53693f02d80e ("drm/i915/dsi: account for DSC in horizontal timings")
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/icl_dsi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/icl_dsi.c b/drivers/gpu/drm/i915/display/icl_dsi.c
> index c04327979678..a763f2b13ff2 100644
> --- a/drivers/gpu/drm/i915/display/icl_dsi.c
> +++ b/drivers/gpu/drm/i915/display/icl_dsi.c
> @@ -888,7 +888,7 @@ gen11_dsi_set_transcoder_timings(struct intel_encoder *encoder,
>  	 * non-compressed link speeds, and simplifies down to the ratio between
>  	 * compressed and non-compressed bpp.
>  	 */
> -	if (crtc_state->dsc.compression_enable) {
> +	if (is_vid_mode(intel_dsi) && crtc_state->dsc.compression_enable) {
>  		mul = fxp_q4_to_int(crtc_state->dsc.compressed_bpp_x16);
>  		div = mipi_dsi_pixel_format_to_bpp(intel_dsi->pixel_format);
>  	}
> @@ -1502,7 +1502,7 @@ static void gen11_dsi_get_timings(struct intel_encoder *encoder,
>  	struct drm_display_mode *adjusted_mode =
>  					&pipe_config->hw.adjusted_mode;
>  
> -	if (pipe_config->dsc.compressed_bpp_x16) {
> +	if (is_vid_mode(intel_dsi) && pipe_config->dsc.compressed_bpp_x16) {
>  		int div = fxp_q4_to_int(pipe_config->dsc.compressed_bpp_x16);
>  		int mul = mipi_dsi_pixel_format_to_bpp(intel_dsi->pixel_format);

-- 
Jani Nikula, Intel