Re: [PATCH 24/24] drm/bridge: establish a link between the bridge supplier and consumer

Daniel Vetter
2018-04-30T15:32:44Z

On Fri, Apr 27, 2018 at 12:31:39AM +0200, Peter Rosin wrote:
> If the bridge supplier is unbound, this will bring the bridge consumer
> down along with the bridge. Thus, there will no longer linger any
> dangling pointers from the bridge consumer (the drm_device) to some
> non-existent bridge supplier.
>
> Signed-off-by: Peter Rosin <peda@axentia.se>

Minus the ->owner bikeshed I brought up in the previous patch I agree with
this approach as the best way to move forward for now.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

One small suggestion below, for merging I'd say pls get Jyri's
review/tested-by too, since you're both working on the same problem it
seems.

Aside: Do you want commit rights to drm-misc to be able to push work like
this?

Cheers, Daniel

> ---
> drivers/gpu/drm/drm_bridge.c | 18 ++++++++++++++++++
> include/drm/drm_bridge.h | 2 ++
> 2 files changed, 20 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index a038da696802..f0c79043ec43 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -26,6 +26,7 @@
> #include <linux/mutex.h>
>
> #include <drm/drm_bridge.h>
> +#include <drm/drm_device.h>
> #include <drm/drm_encoder.h>
>
> #include "drm_crtc_internal.h"
> @@ -124,12 +125,25 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
> if (bridge->dev)
> return -EBUSY;
>
> + if (encoder->dev->dev != bridge->owner) {

You might end up with a NULL encoder->dev->dev. Perhaps check that and
bail with a WARN_ON?

> + bridge->link = device_link_add(encoder->dev->dev,
> + bridge->owner, 0);
> + if (!bridge->link) {
> + dev_err(bridge->owner, "failed to link bridge to %s\n",
> + dev_name(encoder->dev->dev));
> + return -EINVAL;
> + }
> + }
> +
> bridge->dev = encoder->dev;
> bridge->encoder = encoder;
>
> if (bridge->funcs->attach) {
> ret = bridge->funcs->attach(bridge);
> if (ret < 0) {
> + if (bridge->link)
> + device_link_del(bridge->link);
> + bridge->link = NULL;
> bridge->dev = NULL;
> bridge->encoder = NULL;
> return ret;
> @@ -156,6 +170,10 @@ void drm_bridge_detach(struct drm_bridge *bridge)
> if (bridge->funcs->detach)
> bridge->funcs->detach(bridge);
>
> + if (bridge->link)
> + device_link_del(bridge->link);
> + bridge->link = NULL;
> +
> bridge->dev = NULL;
> }
>
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 3bc659f3e7d2..9a386559a41a 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -261,6 +261,7 @@ struct drm_bridge_timings {
> * @list: to keep track of all added bridges
> * @timings: the timing specification for the bridge, if any (may
> * be NULL)
> + * @link: drm consumer <-> bridge supplier
> * @funcs: control functions
> * @driver_private: pointer to the bridge driver's internal context
> */
> @@ -271,6 +272,7 @@ struct drm_bridge {
> struct drm_bridge *next;
> struct list_head list;
> const struct drm_bridge_timings *timings;
> + struct device_link *link;
>
> const struct drm_bridge_funcs *funcs;
> void *driver_private;
> --
> 2.11.0
>
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> dri-devel@lists.freedesktop.org
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--
Daniel Vetter
Software Engineer, Intel Corporation