On Fri, Sep 26, 2025 at 05:59:44PM +0200, Luca Ceresoli wrote: > drm_bridge_attach() modifies the encoder bridge chain, so take a mutex > around such operations to allow users of the chain to protect themselves > from chain modifications while iterating. > > This change does not apply to drm_bridge_detach() because: > * only the drm_encoder.c calls it, not bridge drivers (unlike > drm_bridge_attach()) > * the only drm_bridge_detach() caller is drm_encoder_cleanup() which > already locks the mutex for the entire cleanup loop, thus additionally > locking it here would deadlock > * drm_bridge_detach() is recursively calling itself along the chain, so > care would be needed to avoid deadlocks > Add a comment to clarify that is intended. > > Signed-off-by: Luca Ceresoli <[email protected]> > --- > drivers/gpu/drm/drm_bridge.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > index > 630b5e6594e0affad9ba48791207c7b403da5db8..90e467cf91a134342c80d2f958b928472aaf0d8b > 100644 > --- a/drivers/gpu/drm/drm_bridge.c > +++ b/drivers/gpu/drm/drm_bridge.c > @@ -453,10 +453,12 @@ int drm_bridge_attach(struct drm_encoder *encoder, > struct drm_bridge *bridge, > bridge->dev = encoder->dev; > bridge->encoder = encoder; > > + drm_encoder_chain_lock(encoder); > if (previous) > list_add(&bridge->chain_node, &previous->chain_node); > else > list_add(&bridge->chain_node, &encoder->bridge_chain); > + drm_encoder_chain_unlock(encoder); > > if (bridge->funcs->attach) { > ret = bridge->funcs->attach(bridge, encoder, flags); > @@ -487,7 +489,9 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct > drm_bridge *bridge, > err_reset_bridge: > bridge->dev = NULL; > bridge->encoder = NULL; > + drm_encoder_chain_lock(encoder); > list_del(&bridge->chain_node); > + drm_encoder_chain_unlock(encoder); > > if (ret != -EPROBE_DEFER) > DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n", > @@ -503,6 +507,11 @@ int drm_bridge_attach(struct drm_encoder *encoder, > struct drm_bridge *bridge, > } > EXPORT_SYMBOL(drm_bridge_attach); > > +/* > + * Invoked by the encoder during encoder cleanup in drm_encoder_cleanup(), > + * so should generally *not* be called by driver code.
Why not? Also, it looks entirely unrelated to the rest of the patch.
> As opposed to + * drm_bridge_attach(), does not lock the encoder chain mutex.
> + */ void
> drm_bridge_detach(struct drm_bridge *bridge) { if (WARN_ON(!bridge))
Maxime
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