Re: [RESEND] drm/i915/aux: use polling when irqs are unavailable

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

On Thu, Apr 16, 2026 at 06:37:44PM +0200, Michał Grzelak wrote:
> PTL with physically disconnected display was observed to have 40s longer
> execution time when testing xe_fault_injection@xe_guc_mmio_send_recv.
> The issue has not been seen when reverting commit 40a9f77a28fa ("Revert
> "drm/i915/dp: change aux_ctl reg read to polling read"").
> 
> Apparently the configuration suffers from not having AUX enabled when
> using interrupts. One probable cause can be xe enabling interrupts too
> late: interrupts need memory allocations which currently can't be done
> before the display FB takeover is done.
> 
> As for now, use polling for AUX in case interrupts are unavailable.
> 
> Fixes: 40a9f77a28fa ("Revert "drm/i915/dp: change aux_ctl reg read to polling read"")
> Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Michał Grzelak <michal.grzelak@intel.com>

Pushed to drm-intel-next. Thanks.

> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> index b20ec3e589fad..9c9b6410366d5 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -12,6 +12,7 @@
>  #include "intel_dp.h"
>  #include "intel_dp_aux.h"
>  #include "intel_dp_aux_regs.h"
> +#include "intel_parent.h"
>  #include "intel_pps.h"
>  #include "intel_quirks.h"
>  #include "intel_tc.h"
> @@ -60,18 +61,29 @@ intel_dp_aux_wait_done(struct intel_dp *intel_dp)
>  	struct intel_display *display = to_intel_display(intel_dp);
>  	i915_reg_t ch_ctl = intel_dp->aux_ch_ctl_reg(intel_dp);
>  	const unsigned int timeout_ms = 10;
> +	bool done = true;
>  	u32 status;
> -	bool done;
> +	int ret;
>  
> +	if (intel_parent_irq_enabled(display)) {
>  #define C (((status = intel_de_read_notrace(display, ch_ctl)) & DP_AUX_CH_CTL_SEND_BUSY) == 0)
> -	done = wait_event_timeout(display->gmbus.wait_queue, C,
> -				  msecs_to_jiffies_timeout(timeout_ms));
> +		done = wait_event_timeout(display->gmbus.wait_queue, C,
> +					  msecs_to_jiffies_timeout(timeout_ms));
> +
> +#undef C
> +	} else {
> +		ret = intel_de_wait_ms(display, ch_ctl,
> +				       DP_AUX_CH_CTL_SEND_BUSY, 0,
> +				       timeout_ms, &status);
> +
> +		if (ret == -ETIMEDOUT)
> +			done = false;
> +	}
>  
>  	if (!done)
>  		drm_err(display->drm,
>  			"%s: did not complete or timeout within %ums (status 0x%08x)\n",
>  			intel_dp->aux.name, timeout_ms, status);
> -#undef C
>  
>  	return status;
>  }
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel