Re: [PATCH] drm/probe-helper: fix output polling not resuming after HPD IRQ storm

[Imre Deak <imre.deak@intel.com>]

On Mon, Aug 04, 2025 at 11:13:59PM +0300, Nicusor Huhulea wrote:
> A regression in output polling was introduced by commit 4ad8d57d902fbc7c82507cfc1b031f3a07c3de6e
> ("drm: Check output polling initialized before disabling") in the 6.1.y stable tree.
> As a result, when the i915 driver detects an HPD IRQ storm and attempts to switch
> from IRQ-based hotplug detection to polling, output polling fails to resume.
> 
> The root cause is the use of dev->mode_config.poll_running. Once poll_running is set
> (during the first connector detection) the calls to drm_kms_helper_poll_enable(), such as
> intel_hpd_irq_storm_switch_to_polling() fails to schedule output_poll_work as expected.
> Therefore, after an IRQ storm disables HPD IRQs, polling does not start, breaking hotplug detection.
> 
> The fix is to remove the dev->mode_config.poll_running in the check condition, ensuring polling
> is always scheduled as requested.
> 
> Notes:
>  Initial analysis, assumptions, device testing details, the correct fix and detailed rationale
>  were discussed here https://lore.kernel.org/stable/aI32HUzrT95nS_H9@ideak-desk/
> 
> Cc: stable@vger.kernel.org # 6.1.y
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: Shradha Gupta <shradhagupta@linux.microsoft.com>
> Suggested-by: Imre Deak <imre.deak@intel.com>
> Signed-off-by: Nicusor Huhulea <nicusor.huhulea@siemens.com>

Acked-by: Imre Deak <imre.deak@intel.com>

> ---
>  drivers/gpu/drm/drm_probe_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 0e5eadc6d44d..a515b78f839e 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -250,7 +250,7 @@ void drm_kms_helper_poll_enable(struct drm_device *dev)
>  	unsigned long delay = DRM_OUTPUT_POLL_PERIOD;
>  
>  	if (drm_WARN_ON_ONCE(dev, !dev->mode_config.poll_enabled) ||
> -	    !drm_kms_helper_poll || dev->mode_config.poll_running)
> +	    !drm_kms_helper_poll)
>  		return;
>  
>  	drm_connector_list_iter_begin(dev, &conn_iter);
> -- 
> 2.39.2
>