Re: [PATCH v6 02/18] drm/bridge: inno-hdmi: Don't dereference a NULL drm_device on hotplug

[Heiko Stuebner <heiko@sntech.de>]

Am Donnerstag, 29. Oktober 2026, 08:53:36 Mitteleuropäische Normalzeit schrieb Michal Wilczynski:
> inno_hdmi_irq() passes hdmi->bridge.dev to drm_helper_hpd_irq_event(),
> which dereferences it in its first statement:
> 
> 	if (!dev->mode_config.poll_enabled)
> 
> bridge.dev is assigned only by drm_bridge_attach(), but inno_hdmi_bind()
> unmutes the hotplug interrupt in inno_hdmi_init_hw() and installs the
> handler well before it attaches the bridge:
> 
> 	inno_hdmi_init_hw(hdmi);		/* unmutes hotplug */
> 	devm_request_threaded_irq(...);		/* handler goes live */
> 	...
> 	hdmi->bridge.ddc = inno_hdmi_i2c_adapter(hdmi);
> 	devm_drm_bridge_add(dev, &hdmi->bridge);
> 	drm_bridge_attach(...);			/* bridge.dev set here */
> 
> The bridge is allocated by devm_drm_bridge_alloc(), which kzalloc()s it,
> so bridge.dev is NULL for all of that window, and a hotplug event
> arriving in it enters drm_helper_hpd_irq_event(NULL).
> 
> Before the conversion to a bridge the ordering was safe:
> inno_hdmi_register() called drmm_connector_hdmi_init(), which set
> connector.dev, before the interrupt was requested.
> 
> Drop hotplug events that arrive before the bridge is attached.
> 
> Fixes: 969325a2597e ("drm/rockchip: inno-hdmi: Convert to drm bridge")
> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
> ---
>  drivers/gpu/drm/bridge/inno-hdmi.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/inno-hdmi.c b/drivers/gpu/drm/bridge/inno-hdmi.c
> index d7c33b92e2ddf4ced84d17304463f44be52270b8..d29832249b942dec84fb9d07a0b21ee751fc0486 100644
> --- a/drivers/gpu/drm/bridge/inno-hdmi.c
> +++ b/drivers/gpu/drm/bridge/inno-hdmi.c
> @@ -929,7 +929,13 @@ static irqreturn_t inno_hdmi_irq(int irq, void *dev_id)
>  {
>  	struct inno_hdmi *hdmi = dev_id;
>  
> -	drm_helper_hpd_irq_event(hdmi->bridge.dev);
> +	/*
> +	 * The interrupt is requested before the bridge is attached, and
> +	 * bridge.dev is only set by drm_bridge_attach(). Drop hotplug events
> +	 * that arrive before then rather than dereference a NULL drm_device.
> +	 */
> +	if (hdmi->bridge.dev)
> +		drm_helper_hpd_irq_event(hdmi->bridge.dev);

Reviewed-by: Heiko Stuebner <heiko@sntech.de>

Most other callers of drm_helper_hpd_irq_event() also do exactly this.


Heiko