[Intel-gfx] [PATCH] drm/i915/hdmi: Fix weak connector detection

[Ville Syrjälä]

On Thu, Mar 31, 2016 at 05:55:03PM -0300, Ezequiel Garcia wrote:
> Currently, our implementation of drm_connector_funcs.detect is
> based on getting a valid EDID.
> 
> This requirement makes the driver fail to detect connected
> connectors in case of EDID corruption, which prevents from falling
> back to modes provided by builtin or user-provided EDIDs.

So why are you getting corrupted EDIDs?

> 
> Let's fix this by improving the detection, with a DDC probe,
> if the current EDID-based detection failed.
> 
> Note that a better way of dealing with this could calling
> drm_probe_ddc in drm_connector_funcs.detect, and do the
> EDID full reading and parsing in drm_connector_helper_funcs.get_modes,
> when it's actually needed.
> 
> However, this would be more invasive and thus more error-prone.
> The current commit is an attempt to get some uninvasive fix,
> and allow for easier backporting.
> 
> Signed-off-by: Ezequiel Garcia <ezequiel at vanguardiasur.com.ar>
> ---
>  drivers/gpu/drm/i915/intel_hdmi.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
> index a0d8daed2470..c079206e6681 100644
> --- a/drivers/gpu/drm/i915/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> @@ -1428,6 +1428,20 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
>  	} else
>  		status = connector_status_disconnected;
>  
> +	/*
> +	 * The above call to intel_hdmi_set_edid() checked for a valid EDID.
> +	 * However, the EDID can get corrupted for several reasons, resulting
> +	 * in a disconnected status despite the connector being connected.
> +	 * Hence, let's try one more time, by only probing the DDC.
> +	 *
> +	 * This allows the DRM core to fallback to builtin or user-provided
> +	 * EDID firmware, e.g. in drm_helper_probe_single_connector_modes.
> +	 */
> +	if (status == connector_status_disconnected)
> +		if (drm_probe_ddc(intel_gmbus_get_adapter(dev_priv,
> +						intel_hdmi->ddc_bus)))
> +			status = connector_status_connected;
> +
>  	intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
>  
>  	return status;
> -- 
> 2.7.0
> 
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-- 
Ville Syrjälä
Intel OTC