Re: [PATCH v8 09/39] drm/display: hdmi-state-helper: Add fallback TMDS rate validation

From: Maxime Ripard <mripard@kernel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Cc: "Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"David Airlie" <airlied@gmail.com>,
	"Simona Vetter" <simona@ffwll.ch>,
	"Andrzej Hajda" <andrzej.hajda@intel.com>,
	"Neil Armstrong" <neil.armstrong@linaro.org>,
	"Robert Foss" <rfoss@kernel.org>,
	"Laurent Pinchart" <Laurent.pinchart@ideasonboard.com>,
	"Jonas Karlman" <jonas@kwiboo.se>,
	"Jernej Skrabec" <jernej.skrabec@gmail.com>,
	"Luca Ceresoli" <luca.ceresoli@bootlin.com>,
	"Sandy Huang" <hjc@rock-chips.com>,
	"Heiko Stübner" <heiko@sntech.de>,
	"Andy Yan" <andy.yan@rock-chips.com>,
	"Daniel Stone" <daniels@collabora.com>,
	"Dave Stevenson" <dave.stevenson@raspberrypi.com>,
	"Maíra Canal" <mcanal@igalia.com>,
	"Raspberry Pi Kernel Maintenance" <kernel-list@raspberrypi.com>,
	kernel@collabora.com, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org
Subject: Re: [PATCH v8 09/39] drm/display: hdmi-state-helper: Add fallback TMDS rate validation
Date: Tue, 7 Jul 2026 13:23:25 +0200	[thread overview]
Message-ID: <20260707-venomous-helpful-magpie-b2962b@penduick> (raw)
In-Reply-To: <20260702-dw-hdmi-qp-scramb-v8-9-d79890d00b6a@collabora.com>

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Hi,

On Thu, Jul 02, 2026 at 05:46:22PM +0300, Cristian Ciocaltea wrote:
> Validate the computed TMDS character rate against
> connector->hdmi.max_tmds_char_rate when no driver-specific
> tmds_char_rate_valid() hook is provided.
> 
> This gives HDMI connectors a common fallback for rejecting modes whose
> TMDS character rate exceeds the connector limit, while still allowing
> drivers with custom validation requirements to implement their own
> tmds_char_rate_valid() callback.
> 
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> ---
>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index ce17eeefc2da..db76699093e8 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -566,6 +566,9 @@ hdmi_clock_valid(const struct drm_connector *connector,
>  		status = funcs->tmds_char_rate_valid(connector, mode, clock);
>  		if (status != MODE_OK)
>  			return status;
> +	} else if (connector->hdmi.max_tmds_char_rate) {
> +		if (clock > connector->hdmi.max_tmds_char_rate)
> +			return MODE_CLOCK_HIGH;

I think we should handle this the same way we do for
info->max_tmds_clock: if it's set, we always check that before calling
the driver.

It reduces the boilerplate in drivers, and it's always a relevant check
anyway.

Maxime

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