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

[Dmitry Baryshkov]

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.

Why doesn't disable path use drm_kms_helper_poll_disable() ?

> 
> 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/
> 

-- 
With best wishes
Dmitry