[PATCH 1/6] drm/display: hdmi: add generic mode_valid helper

[Dmitry Baryshkov]

On Mon, Oct 21, 2024 at 11:32:03AM +0200, Maxime Ripard wrote:
> On Fri, Oct 18, 2024 at 11:34:19PM +0300, Dmitry Baryshkov wrote:
> > Add drm_hdmi_connector_mode_valid(), generic helper for HDMI connectors.
> > It can be either used directly or as a part of the .mode_valid callback.
> > 
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> > ---
> >  drivers/gpu/drm/display/drm_hdmi_helper.c | 25 +++++++++++++++++++++++++
> >  include/drm/display/drm_hdmi_helper.h     |  4 ++++
> >  2 files changed, 29 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/display/drm_hdmi_helper.c b/drivers/gpu/drm/display/drm_hdmi_helper.c
> > index 74dd4d01dd9b..0ac5cb000ee2 100644
> > --- a/drivers/gpu/drm/display/drm_hdmi_helper.c
> > +++ b/drivers/gpu/drm/display/drm_hdmi_helper.c
> > @@ -256,3 +256,28 @@ drm_hdmi_compute_mode_clock(const struct drm_display_mode *mode,
> >  	return DIV_ROUND_CLOSEST_ULL(clock * bpc, 8);
> >  }
> >  EXPORT_SYMBOL(drm_hdmi_compute_mode_clock);
> > +
> > +/**
> > + * drm_hdmi_connector_mode_valid() - Check if mode is valid for HDMI connector
> > + * @connector: DRM connector to validate the mode
> > + * @mode: Display mode to validate
> > + *
> > + * Generic .mode_valid implementation for HDMI connectors.
> > + */
> > +enum drm_mode_status
> > +drm_hdmi_connector_mode_valid(const struct drm_connector *connector,
> > +			      const struct drm_display_mode *mode)
> > +{
> > +	const struct drm_connector_hdmi_funcs *funcs = connector->hdmi.funcs;
> > +	unsigned long long rate;
> > +
> > +	rate = drm_hdmi_compute_mode_clock(mode, 8, HDMI_COLORSPACE_RGB);
> > +	if (!rate)
> > +		return MODE_ERROR;
> > +
> > +	if (!funcs || !funcs->tmds_char_rate_valid)
> > +		return MODE_OK;
> > +
> > +	return funcs->tmds_char_rate_valid(connector, mode, rate);
> > +}
> > +EXPORT_SYMBOL(drm_hdmi_connector_mode_valid);
> 
> As discussed in the discussion that sparked that change, I believe that
> we should use hdmi_clock_valid.

Ack, I will modify the code accordingly.

> 
> AFAIU, your concern was that max_tmds_clock might get stale, but then it
> would not only prevent mode_valid from running but also the commit
> entirely.

It might be stale when parsing / validating the modes. But let's try
landing it the way you had in mind and fix the drivers which misbehave
(if any).

> 
> We don't have any evidence from that, so I'd rather try to keep
> consistency between the two. And we can always try to address whatever
> issue we might have if it turned out to be a bad idea :)

-- 
With best wishes
Dmitry