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
