Re: [PATCH 2/4 v3] drm: Introduce drm_connector_register_all() helper

[Alexey Brodkin <Alexey.Brodkin@synopsys.com>]

Hi David,

On Wed, 2016-03-23 at 12:13 +0100, David Herrmann wrote:
> Hi
> 
> On Wed, Mar 23, 2016 at 9:42 AM, Alexey Brodkin
> <Alexey.Brodkin@synopsys.com> wrote:
> > 
> > As a pair to already existing drm_connector_unregister_all() we're adding
> > generic implementation of what is already done in some drivers.
> > 
> > Once this helper is implemented we'll be ready to switch existing
> > driver-specific implementations with the generic one.
> > 
> > Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: David Airlie <airlied@linux.ie>
> > ---
> > 
> > Changes v2 -> v3:
> >  * Updated title with capital after colon
> >  * Simplified failure path with direct and unconditional invocation of
> >    unregister_all()
> >  * Updated kerneldoc description of the drm_connector_register_all()
> > 
> > Changes v1 -> v2:
> >  * Rename drm_connector_unplug_all() to drm_connector_unregister_all()
> >  * Use drm_for_each_connector() instead of list_for_each_entry()
> >  * Updated kerneldoc for drm_dev_register()
> > 
> >  drivers/gpu/drm/drm_crtc.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/drm_drv.c  |  6 +++++-
> >  include/drm/drm_crtc.h     |  3 ++-
> >  3 files changed, 50 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> > index 65488a6..21eea11 100644
> > --- a/drivers/gpu/drm/drm_crtc.c
> > +++ b/drivers/gpu/drm/drm_crtc.c
> > @@ -1081,6 +1081,49 @@ void drm_connector_unregister(struct drm_connector *connector)
> >  EXPORT_SYMBOL(drm_connector_unregister);
> > 
> >  /**
> > + * drm_connector_register_all - register all connectors
> > + * @dev: drm device
> > + *
> > + * This function registers all connectors in sysfs and other places so that
> > + * userspace can start to access them. Drivers can call it after calling
> > + * drm_dev_register() to complete the device registration, if they don't call
> > + * drm_connector_register() on each connector individually.
> > + *
> > + * When a device is unplugged and should be removed from userspace access,
> > + * call drm_connector_unregister_all(), which is the inverse of this
> > + * function.
> > + *
> > + * Returns:
> > + * Zero on success, error code on failure.
> > + */
> > +int drm_connector_register_all(struct drm_device *dev)
> > +{
> > +       struct drm_connector *connector;
> > +       int ret;
> > +
> > +       mutex_lock(&dev->mode_config.mutex);
> > +
> > +       drm_for_each_connector(connector, dev) {
> > +               ret = drm_connector_register(connector);
> > +               if (ret) {
> > +                       /*
> > +                        * We may safely call unregister_all() here within
> > +                        * area locked with mutex because unregister_all()
> > +                        * doesn't use locks inside (see a comment in that
> > +                        * function).
> > +                        */
> Ugh? unregister_all() says:
> 
> /* FIXME: taking the mode config mutex ends up in a clash with sysfs */
> 
> This strongly contradicts your comment. Anyway, regardless how you
> want to fix it: You better unlock the mode-config mutex before
> returning below.

So good catch.
But what I really meant since we didn't get any further after registering
all "good" connections (see we're not releasing mutex still) the will be
no clashes with sysfs.

Still I;d like Daniel to comment on that separately.

-Alexey