linux-kernel - Re: [PATCH] drm/i915/hdmi: enable resolution 3840x2160 for type 1 HDMI

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Date:   Wed, 16 Oct 2019 13:33:06 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Jian-Hong Pan <jian-hong@...lessm.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Ramalingam C <ramalingam.c@...el.com>,
        Uma Shankar <uma.shankar@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux@...lessm.com
Subject: Re: [PATCH] drm/i915/hdmi: enable resolution 3840x2160 for type 1
 HDMI

On Wed, Oct 16, 2019 at 05:57:58PM +0800, Jian-Hong Pan wrote:
> Type 1 HDMI may be version 1.3 or upper, which supports higher max TMDS
> clock for higher resolutions,

Spec says "Type 1 adaptors can support DVI or HDMI up to a 165MHz TMDS clock rate."

And I've definitely seen HDMI dongles that can't deal with
eg. 1080p 12bpc @225MHz. We don't want users with black screens
out of the box, so NAK.

If you want to "overclock" your hardware you can do so by setting up
the modeline manually.

> like 3840x2160. This patch sets max TMDS
> clock according to the chip, if the adapter is type 1 HDMI.
> 
> Buglink: https://bugs.freedesktop.org/show_bug.cgi?id=112018
> Fixes: b1ba124d8e95 ("drm/i915: Respect DP++ adaptor TMDS clock limit")
> Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> ---
>  drivers/gpu/drm/i915/display/intel_hdmi.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> index e02f0faecf02..74e4426ffcad 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> @@ -2454,6 +2454,7 @@ intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector, bool has_edid)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(connector->dev);
>  	struct intel_hdmi *hdmi = intel_attached_hdmi(connector);
> +	struct intel_encoder *encoder = &hdmi_to_dig_port(hdmi)->base;
>  	enum port port = hdmi_to_dig_port(hdmi)->base.port;
>  	struct i2c_adapter *adapter =
>  		intel_gmbus_get_adapter(dev_priv, hdmi->ddc_bus);
> @@ -2488,8 +2489,16 @@ intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector, bool has_edid)
>  		return;
>  
>  	hdmi->dp_dual_mode.type = type;
> -	hdmi->dp_dual_mode.max_tmds_clock =
> -		drm_dp_dual_mode_max_tmds_clock(type, adapter);
> +	/* Type 1 HDMI may be version 1.3 or upper, which supports higher max
> +	 * TMDS clock for higher resolutions, like 3840x2160. So, set it
> +	 * according to the chip, if the adapter is type 1 HDMI.
> +	 */
> +	if (type == DRM_DP_DUAL_MODE_TYPE1_HDMI)
> +		hdmi->dp_dual_mode.max_tmds_clock =
> +			intel_hdmi_source_max_tmds_clock(encoder);
> +	else
> +		hdmi->dp_dual_mode.max_tmds_clock =
> +			drm_dp_dual_mode_max_tmds_clock(type, adapter);
>  
>  	DRM_DEBUG_KMS("DP dual mode adaptor (%s) detected (max TMDS clock: %d kHz)\n",
>  		      drm_dp_get_dual_mode_type_name(type),
> -- 
> 2.23.0

-- 
Ville Syrjälä
Intel