Re: [PATCH] drm/vc4: hdmi: Unregister the ASoC card on unbind

[Karl Mehltretter <kmehltretter@gmail.com>]

On Mon, Aug 24, 2026 at 08:52:44AM +0100, Maxime Ripard wrote:
> And that happens only because you have no user. If you had one, you
> would have had the opposite sequence.
> 

Hi Maxime,

Thanks for the correction, and sorry that v1 described the lifetime too
broadly.

You are right that DRM-managed memory is released when the last DRM
reference is gone, not simply at unbind. With an open DRM fd, vc4_hdmi can
outlive platform teardown.

v2 was triggered by syzbot comments on the ASoC retry path. A deferred card
bind can move the devm registration outside the component devres
group. With no DRM fd open, the final DRM release can then free vc4_hdmi
before the HDMI platform releases the card.

v2 link:
https://lore.kernel.org/r/20260823173740.2983-1-kmehltretter@gmail.com/

I will send a v3 based on your input.

The implementation change was already in v2. v3 only clarifies the wording
and keeps that same implementation. The card is registered without devm and
unregistered from component unbind while vc4_hdmi is still alive.

I also tested this on a real Pi 400 with /dev/dri/card0 open during vc4-drm
sysfs unbind. There were no new KASAN reports.

Thanks,
Karl