Hi, On Mon, Jan 16, 2023 at 03:22:34PM +0800, Chen-Yu Tsai wrote: > The device lock is used to serialize the low level power sequencing > operations. Since drm_helper_hpd_irq_event() could end up calling > .atomic_enable, which also calls power sequencing functions through > runtime PM, this results in a real deadlock. This was observed on an > MT8192-based Chromebook's external display (with appropriate patches [1] > and DT changes applied). > > Move the drm_helper_hpd_irq_event() call outside of the lock range. The > lock only needs to be held so that the device status can be read back. > This is the bare minimum change to avoid the deadlock. The lock could > be dropped completely and have pm_runtime_get_if_in_use() increase the > reference count, but this is not the same as pm_runtime_suspended(). > This also causes the internal display of the same device to not > function correctly. Both the internal and external display of said > device each use one anx7625 bridge. > > [1] > https://lore.kernel.org/dri-devel/20230112042104.4107253-1-treapk...@chromium.org/ > > Fixes: 60487584a79a ("drm/bridge: anx7625: refactor power control to use > runtime PM framework") > Signed-off-by: Chen-Yu Tsai <we...@chromium.org> > --- > FWIW I'm aware that this driver could be refactored a lot better. > The work function might be simplified and merged into the threaded > interrupt handler. The .detect op should be reading the HPD state > from the hardware, not some cached state. > > drivers/gpu/drm/bridge/analogix/anx7625.c | 13 ++++++------- > 1 file changed, 6 insertions(+), 7 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c > b/drivers/gpu/drm/bridge/analogix/anx7625.c > index 7e1fb93a6ce4..bf1770b79bba 100644 > --- a/drivers/gpu/drm/bridge/analogix/anx7625.c > +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c > @@ -1597,18 +1597,17 @@ static void anx7625_work_func(struct work_struct > *work) > > mutex_lock(&ctx->lock); > > - if (pm_runtime_suspended(&ctx->client->dev)) > - goto unlock; > + if (pm_runtime_suspended(&ctx->client->dev)) { > + mutex_unlock(&ctx->lock); > + return; > + } > > event = anx7625_hpd_change_detect(ctx); > - if (event < 0)
Are you intentionally dropping this early-return on error? > - goto unlock; > + > + mutex_unlock(&ctx->lock); > > if (ctx->bridge_attached) > drm_helper_hpd_irq_event(ctx->bridge.dev); > - > -unlock: > - mutex_unlock(&ctx->lock); > } > > static irqreturn_t anx7625_intr_hpd_isr(int irq, void *data) > -- > 2.39.0.314.g84b9a713c41-goog >
