Re: [Intel-gfx] [PATCH RESEND v3 1/3] drm/i915/dp_mst: Fix disabling MST on a port

["Souza, Jose" <jose.souza@intel.com>]

On Fri, 2020-06-05 at 12:48 +0300, Imre Deak wrote:
> Currently MST on a port can get enabled/disabled from the hotplug work
> and get disabled from the short pulse work in a racy way. Fix this by
> relying on the MST state checking in the hotplug work and just schedule
> a hotplug work from the short pulse handler if some problem happened
> during the MST interrupt handling.
> 
> This removes the explicit MST disabling in case of an AUX failure, but
> if AUX fails, then probably the detection will also fail during the
> scheduled hotplug work and it's not guaranteed that we'll see
> intermittent errors anyway.
> 
> While at it also simplify the error checking of the MST interrupt
> handler.
> 
> v2:
> - Convert intel_dp_check_mst_status() to return bool. (Ville)
> - Change the intel_dp->is_mst check to an assert, since after this patch
>   the condition can't change after we checked it previously.
> - Document the return value from intel_dp_check_mst_status().
> v3:
> - Remove the intel_dp->is_mst check from intel_dp_check_mst_status().
>   There is no point in checking the same condition twice, even though
>   there is a chance that the hotplug work running concurrently changes
>   it.
> 
> Cc: José Roberto de Souza <jose.souza@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Reviewed-by: José Roberto de Souza <jose.souza@intel.com> (v1)
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 66 ++++++++++---------------
>  1 file changed, 26 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 55fda074c0ad..42589cae766d 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5556,35 +5556,46 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
>  			    "Could not write test response to sink\n");
>  }
>  
> -static int
> +/**
> + * intel_dp_check_mst_status - service any pending MST interrupts, check link status
> + * @intel_dp: Intel DP struct
> + *
> + * Read any pending MST interrupts, call MST core to handle these and ack the
> + * interrupts. Check if the main and AUX link state is ok.
> + *
> + * Returns:
> + * - %true if pending interrupts were serviced (or no interrupts were
> + *   pending) w/o detecting an error condition.
> + * - %false if an error condition - like AUX failure or a loss of link - is
> + *   detected, which needs servicing from the hotplug work.
> + */
> +static bool
>  intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  {
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	bool need_retrain = false;
> -
> -	if (!intel_dp->is_mst)
> -		return -EINVAL;
> +	bool link_ok = true;
>  
>  	drm_WARN_ON_ONCE(&i915->drm, intel_dp->active_mst_links < 0);
>  
>  	for (;;) {
>  		u8 esi[DP_DPRX_ESI_LEN] = {};
> -		bool bret, handled;
> +		bool handled;
>  		int retry;
>  
> -		bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
> -		if (!bret) {
> +		if (!intel_dp_get_sink_irq_esi(intel_dp, esi)) {
>  			drm_dbg_kms(&i915->drm,
>  				    "failed to get ESI - device may have failed\n");
> -			return -EINVAL;
> +			link_ok = false;
> +
> +			break;
>  		}
>  
>  		/* check link status - esi[10] = 0x200c */
> -		if (intel_dp->active_mst_links > 0 && !need_retrain &&
> +		if (intel_dp->active_mst_links > 0 && link_ok &&
>  		    !drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
>  			drm_dbg_kms(&i915->drm,
>  				    "channel EQ not ok, retraining\n");
> -			need_retrain = true;
> +			link_ok = false;
>  		}
>  
>  		drm_dbg_kms(&i915->drm, "got esi %3ph\n", esi);
> @@ -5604,7 +5615,7 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  		}
>  	}
>  
> -	return need_retrain;
> +	return link_ok;
>  }
>  
>  static bool
> @@ -7255,35 +7266,10 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>  	}
>  
>  	if (intel_dp->is_mst) {
> -		switch (intel_dp_check_mst_status(intel_dp)) {
> -		case -EINVAL:
> -			/*
> -			 * If we were in MST mode, and device is not
> -			 * there, get out of MST mode
> -			 */
> -			drm_dbg_kms(&i915->drm,
> -				    "MST device may have disappeared %d vs %d\n",
> -				    intel_dp->is_mst,
> -				    intel_dp->mst_mgr.mst_state);
> -			intel_dp->is_mst = false;
> -			drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr,
> -							intel_dp->is_mst);
> -
> -			return IRQ_NONE;
> -		case 1:
> -			return IRQ_NONE;
> -		default:
> -			break;
> -		}
> -	}
> -
> -	if (!intel_dp->is_mst) {
> -		bool handled;
> -
> -		handled = intel_dp_short_pulse(intel_dp);
> -
> -		if (!handled)
> +		if (!intel_dp_check_mst_status(intel_dp))
>  			return IRQ_NONE;
> +	} else if (!intel_dp_short_pulse(intel_dp)) {
> +		return IRQ_NONE;
>  	}
>  

Now it don't need the braces but this is minor.

Reviewed-by: José Roberto de Souza <jose.souza@intel.com>

>  	return IRQ_HANDLED;
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