[Intel-gfx] [PATCH 2/2] drm/i915: Extend hotplug detect retry on TypeC connectors to 5 seconds

[Anshuman Gupta]

On 2020-03-30 at 15:24:25 +0530, Imre Deak wrote:
> On TypeC ports if a sink deasserts/reasserts its HPD signal, generating
> a hotplug interrupt without the sink getting unplugged/replugged from
> the connector, there can be an up to 3 seconds delay until the AUX
> channel gets functional. To avoid detection failures this delay causes
> retry the detection for 5 seconds.
> 
> I noticed this on ICL/TGL RVPs and a DELL XPS 13 7390 ICL laptop.
> 
> References: https://gitlab.freedesktop.org/drm/intel/issues/1067
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index 4f508bf70f3b..2d947ff83488 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -4371,7 +4371,10 @@ static enum intel_hotplug_state
>  intel_ddi_hotplug(struct intel_encoder *encoder,
>  		  struct intel_connector *connector)
>  {
> +	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
>  	struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
> +	enum phy phy = intel_port_to_phy(i915, encoder->port);
> +	bool is_tc = intel_phy_is_tc(i915, phy);
>  	struct drm_modeset_acquire_ctx ctx;
>  	enum intel_hotplug_state state;
>  	int ret;
> @@ -4414,8 +4417,15 @@ intel_ddi_hotplug(struct intel_encoder *encoder,
>  	 * valid EDID. To solve this schedule another detection cycle if this
>  	 * time around we didn't detect any change in the sink's connection
>  	 * status.
> +	 *
> +	 * Type-c connectors which get their HPD signal deasserted then
> +	 * reasserted, without unplugging/replugging the sink from the
> +	 * connector, introduce a delay until the AUX channel communication
> +	 * becomes functional. Retry the detection for 5 seconds on type-c
> +	 * connectors to account for this delay.
>  	 */
> -	if (state == INTEL_HOTPLUG_UNCHANGED && !connector->hotplug_retries &&
> +	if (state == INTEL_HOTPLUG_UNCHANGED &&
> +	    connector->hotplug_retries < (is_tc ? 5 : 1) &&
I had observed that intel_dp_detect may race between user spece invoked
get connector call and intel_encoder_hotplug(), that may leave connector status
to be UNCHANGED in actual hotplug flow as intel_dp_detect() already called from 
drm_helper_probe_single_connector_modes(), this may results in 5 retries for 
type-C ports for normal HPD assertion.
Please correct me if i am wrong.
Thanks,
Anshuman Gupta.
>  	    !dig_port->dp.is_mst)
>  		state = INTEL_HOTPLUG_RETRY;
>  
> -- 
> 2.23.1
> 
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