[PATCH 04/20] drm/i915/dp: Handle a tunneling IRQ after acking it

[Luca Coelho]

On Thu, 2025-06-26 at 11:20 +0300, Imre Deak wrote:
> From: Imre Deak <imre.deak at gmail.com>
> 
> HPD IRQs in general should be handled after acking them. The
> 
> 1. Read IRQ register (read DP_DEVICE_SERVICE_IRQ_VECTOR,
>    DP_LINK_SERVICE_IRQ_VECTOR_ESI0)
> 2. Handle IRQ
> 3. Ack IRQ (write DP_DEVICE_SERVICE_IRQ_VECTOR,
>    DP_LINK_SERVICE_IRQ_VECTOR_ESI0)
> 
> sequence would miss a new interrupt triggered after 2. and before 3.,
> since the flag set in the IRQ register for this interrupt would be
> cleared in step 3.
> 
> Fix the above by handling the IRQ after acking it.
> 
> Signed-off-by: Imre Deak <imre.deak at gmail.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 285cd9a5d4a7b..453416b9e9bec 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5099,17 +5099,10 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  
>  		drm_dbg_kms(display->drm, "DPRX ESI: %4ph\n", esi);
>  
> -		ack[3] |= esi[3] & LINK_STATUS_CHANGED;
> +		ack[3] |= esi[3] & (LINK_STATUS_CHANGED | DP_TUNNELING_IRQ);
>  
>  		intel_dp_mst_hpd_irq(intel_dp, esi, ack);
>  
> -		if (esi[3] & DP_TUNNELING_IRQ) {
> -			if (drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> -						     &intel_dp->aux))
> -				reprobe_needed = true;
> -			ack[3] |= DP_TUNNELING_IRQ;
> -		}
> -
>  		if (mem_is_zero(ack, sizeof(ack)))
>  			break;

What happens if we ack the interrupt, but end up not handling it, e.g.
if mem_is_zero() returns true here?


>  
> @@ -5121,6 +5114,10 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>  
>  		if ((ack[3] & LINK_STATUS_CHANGED) || intel_dp->link.force_retrain)
>  			intel_dp_check_link_state(intel_dp);
> +
> +		if ((ack[3] & DP_TUNNELING_IRQ) &&
> +		    drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr, &intel_dp->aux))
> +			reprobe_needed = true;
>  	}
>  
>  	return !reprobe_needed;
> @@ -5423,18 +5420,18 @@ static bool intel_dp_check_link_service_irq(struct intel_dp *intel_dp)
>  			      DP_LINK_SERVICE_IRQ_VECTOR_ESI0, &val) != 1 || !val)
>  		return false;
>  
> -	if ((val & DP_TUNNELING_IRQ) &&
> -	    drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> -				     &intel_dp->aux))
> -		reprobe_needed = true;
> -
>  	if (drm_dp_dpcd_writeb(&intel_dp->aux,
>  			       DP_LINK_SERVICE_IRQ_VECTOR_ESI0, val) != 1)
> -		return reprobe_needed;
> +		return false;
>  
>  	if (val & HDMI_LINK_STATUS_CHANGED)
>  		intel_dp_handle_hdmi_link_status_change(intel_dp);
>  
> +	if ((val & DP_TUNNELING_IRQ) &&
> +	    drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> +				     &intel_dp->aux))
> +		reprobe_needed = true;
> +
>  	return reprobe_needed;
>  }
>  

--
Cheers,
Luca.