linux-kernel - Re: [PATCH 1/6] drm/display: hdmi: add generic mode

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Message-ID: <2az2ja5zrd5kw4iusvl23grvrgjcvh7jcyw66kjdsh2gftvmkb@araqcfpv246x>
Date: Mon, 21 Oct 2024 16:44:31 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Chen-Yu Tsai <wens@...e.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Dave Stevenson <dave.stevenson@...pberrypi.com>, Maíra Canal <mcanal@...lia.com>, 
	Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 1/6] drm/display: hdmi: add generic mode_valid helper

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@...aro.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