Re: [PATCH v12 05/25] drm/atomic-helper: Add HDMI bridge output bus formats helper

Dmitry Baryshkov
2026-04-09T22:09:06Z

On Thu, Apr 09, 2026 at 05:44:55PM +0200, Nicolas Frattaroli wrote:
> The drm_bridge_funcs atomic_get_output_bus_fmts operation should be the
> same for likely every HDMI connector bridge, unless such an HDMI
> connector bridge has some special hardware restrictions that I cannot
> envision yet.
>
> To avoid code duplication and standardize on a set of media bus formats
> that the HDMI output color formats translate to, add a common helper
> function that implements this operation to the drm bridge helpers.
>
> The function returns a list of output bus formats based on the HDMI
> bridge's current output bits-per-component, and its bitmask of supported
> color formats.
>
> To guard against future expansion of DRM_OUTPUT_COLOR_FORMAT outgrowing
> the hweight8 call, add a BUILD_BUG_ON statement where it's used that
> checks for DRM_OUTPUT_COLOR_FORMAT_COUNT. The justification for not
> using hweight32 in all cases is that not all ISAs have a popcount
> instruction, and will benefit from a smaller/faster software
> implementation that doesn't have to operate across all bits.
>
> The justification for not defining an hweight_color depending on the
> value of DRM_OUTPUT_COLOR_FORMAT_COUNT is that this count enum value is
> only known at compile time, not at preprocessor time.
>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
> drivers/gpu/drm/drm_atomic_helper.c | 81 +++++++++++++++++++++++++++++++++++++
> include/drm/drm_atomic_helper.h | 7 ++++
> 2 files changed, 88 insertions(+)
>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

--
With best wishes
Dmitry