On Fri, Sep 26, 2025 at 05:59:42PM +0200, Luca Ceresoli wrote: > The per-encoder bridge chain is currently assumed to be static once it is > fully initialized. Work is in progress to add hot-pluggable bridges, > breaking that assumption. > > With bridge removal, the encoder chain can change without notice, removing > tail bridges. This can be problematic while iterating over the chain. > > Add a mutex to be taken whenever looping or changing the encoder chain. > > Also add two APIs to lock/unlock the mutex without the need to manipulate > internal struct drm_encoder fields. > > Signed-off-by: Luca Ceresoli <[email protected]> > --- > drivers/gpu/drm/drm_encoder.c | 2 ++ > include/drm/drm_encoder.h | 18 ++++++++++++++++++ > 2 files changed, 20 insertions(+) > > diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c > index > 8f2bc6a28482229fd0b030a1958f87753ad7885f..3261f142baea30c516499d23dbf8d0acf5952cd6 > 100644 > --- a/drivers/gpu/drm/drm_encoder.c > +++ b/drivers/gpu/drm/drm_encoder.c > @@ -129,6 +129,7 @@ static int __drm_encoder_init(struct drm_device *dev, > } > > INIT_LIST_HEAD(&encoder->bridge_chain); > + mutex_init(&encoder->bridge_chain_mutex); > list_add_tail(&encoder->head, &dev->mode_config.encoder_list); > encoder->index = dev->mode_config.num_encoder++; > > @@ -202,6 +203,7 @@ void drm_encoder_cleanup(struct drm_encoder *encoder) > kfree(encoder->name); > list_del(&encoder->head); > dev->mode_config.num_encoder--; > + mutex_destroy(&encoder->bridge_chain_mutex); > > memset(encoder, 0, sizeof(*encoder)); > } > diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h > index > 977a9381c8ba943b4d3e021635ea14856df8a17d..6c962de640a345bfbb18308c83076628547c9ab9 > 100644 > --- a/include/drm/drm_encoder.h > +++ b/include/drm/drm_encoder.h > @@ -25,6 +25,7 @@ > > #include <linux/list.h> > #include <linux/ctype.h> > +#include <linux/mutex.h> > #include <drm/drm_crtc.h> > #include <drm/drm_mode.h> > #include <drm/drm_mode_object.h> > @@ -189,6 +190,9 @@ struct drm_encoder { > */ > struct list_head bridge_chain; > > + /** @bridge_chain_mutex: protect bridge_chain from changes while > iterating */ > + struct mutex bridge_chain_mutex; > + > const struct drm_encoder_funcs *funcs; > const struct drm_encoder_helper_funcs *helper_private; > > @@ -319,6 +323,20 @@ static inline struct drm_encoder > *drm_encoder_find(struct drm_device *dev, > return mo ? obj_to_encoder(mo) : NULL; > } > > +static inline struct drm_encoder *drm_encoder_chain_lock(struct drm_encoder > *encoder) > +{ > + if (!WARN_ON_ONCE(!encoder)) > + mutex_lock(&encoder->bridge_chain_mutex); > + > + return encoder; > +} > + > +static inline void drm_encoder_chain_unlock(struct drm_encoder *encoder) > +{ > + if (!WARN_ON_ONCE(!encoder)) > + mutex_unlock(&encoder->bridge_chain_mutex); > +} > +
Please provide documentation for these two functions. In particular, why do we need to return the encoder pointer? Maxime
signature.asc
Description: PGP signature
