Re: [PATCH] drm/i915/vbt: ignore extraneous child devices for a port

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Aug 11, 2017 at 02:39:07PM +0300, Jani Nikula wrote:
> Ever since we've parsed VBT child devices, starting from 6acab15a7b0d
> ("drm/i915: use the HDMI DDI buffer translations from VBT"), we've
> ignored the child device information if more than one child device
> references the same port. The rationale for this seems lost in time.
> 
> Since commit 311a20949f04 ("drm/i915: don't init DP or HDMI when not
> supported by DDI port") we started using this information more to skip
> HDMI/DP init if the port wasn't there per VBT child devices. However, at
> the same time it added port defaults without further explanation.
> 
> Thus, if the child device info was skipped due to multiple child devices
> referencing the same port, the device info would be retrieved from the
> somewhat arbitrary defaults.
> 
> Finally, when commit bb1d132935c2 ("drm/i915/vbt: split out defaults
> that are set when there is no VBT") stopped initializing the defaults
> whenever VBT is present, thus trusting the VBT more, we stopped
> initializing ports which were referenced by more than one child device.
> 
> Apparently at least Asus UX305UA, UX305U, and UX306U laptops have VBT
> child device blocks which cause this behaviour. Arguably they were
> shipped with a broken VBT.
> 
> Relax the rules for multiple references to the same port, and use the
> first child device info to reference a port. Retain the logic to debug
> log about this, though.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101745
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196233
> Fixes: bb1d132935c2 ("drm/i915/vbt: split out defaults that are set when there is no VBT")
> Tested-by: Oliver Wei�barth <mail@oweissbarth.de>
> Reported-by: Oliver Wei�barth <mail@oweissbarth.de>
> Reported-by: Didier G <didierg-divers@orange.fr>
> Reported-by: Giles Anderson <agander@gmail.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Cc: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Cc: <stable@vger.kernel.org> # v4.12+
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_bios.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> index 82b144cdfa1d..183e87e8ea31 100644
> --- a/drivers/gpu/drm/i915/intel_bios.c
> +++ b/drivers/gpu/drm/i915/intel_bios.c
> @@ -1120,8 +1120,8 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
>  	bool is_dvi, is_hdmi, is_dp, is_edp, is_crt;
>  	uint8_t aux_channel, ddc_pin;
>  	/* Each DDI port can have more than one value on the "DVO Port" field,
> -	 * so look for all the possible values for each port and abort if more
> -	 * than one is found. */
> +	 * so look for all the possible values for each port.
> +	 */
>  	int dvo_ports[][3] = {
>  		{DVO_PORT_HDMIA, DVO_PORT_DPA, -1},

So at least one of the machines has dvo_port==HDMI-A in the VBT
alongside DP-A. HDMI-A is not really legal on any platform IIRC, so we
might want to reject it outright. But on the other hand, we've seen a
lot of VBTs that make a real mess of the dvo_port type vs. the device_type
bits, and thus we often consider both HDMI and DP dvo_ports to be valid
for either port type. So I guess it might be possible that there are VBTs
out there that rely on HDMI-A being picked up.

Either way the patch seems about as sane as anything else relating to VBT so
Reviewed-by: Ville Syrj�l� <ville.syrjala@linux.intel.com>

>  		{DVO_PORT_HDMIB, DVO_PORT_DPB, -1},
> @@ -1130,7 +1130,10 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
>  		{DVO_PORT_CRT, DVO_PORT_HDMIE, DVO_PORT_DPE},
>  	};
>  
> -	/* Find the child device to use, abort if more than one found. */
> +	/*
> +	 * Find the first child device to reference the port, report if more
> +	 * than one found.
> +	 */
>  	for (i = 0; i < dev_priv->vbt.child_dev_num; i++) {
>  		it = dev_priv->vbt.child_dev + i;
>  
> @@ -1140,11 +1143,11 @@ static void parse_ddi_port(struct drm_i915_private *dev_priv, enum port port,
>  
>  			if (it->common.dvo_port == dvo_ports[port][j]) {
>  				if (child) {
> -					DRM_DEBUG_KMS("More than one child device for port %c in VBT.\n",
> +					DRM_DEBUG_KMS("More than one child device for port %c in VBT, using the first.\n",
>  						      port_name(port));
> -					return;
> +				} else {
> +					child = it;
>  				}
> -				child = it;
>  			}
>  		}
>  	}
> -- 
> 2.11.0

-- 
Ville Syrj�l�
Intel OTC