linux-kernel - Re: [PATCH 2/4 v3] drm: Introduce drm_connector_register

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Message-ID: <20160329125249.GX2510@phenom.ffwll.local>
Date:	Tue, 29 Mar 2016 14:52:49 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Cc:	"daniel@...ll.ch" <daniel@...ll.ch>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dh.herrmann@...il.com" <dh.herrmann@...il.com>,
	"airlied@...ux.ie" <airlied@...ux.ie>
Subject: Re: [PATCH 2/4 v3] drm: Introduce drm_connector_register_all() helper

On Tue, Mar 29, 2016 at 09:12:38AM +0000, Alexey Brodkin wrote:
> Hi Daniel,
> 
> On Tue, 2016-03-29 at 10:19 +0200, Daniel Vetter wrote:
> > On Wed, Mar 23, 2016 at 01:41:05PM +0000, Alexey Brodkin wrote:
> > > 
> > > 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@...opsys.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@...opsys.com>
> > > > > Cc: Daniel Vetter <daniel@...ll.ch>
> > > > > Cc: David Airlie <airlied@...ux.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.
> > I think doing the unregister_all outside of the loop&locked section is
> > better for future-proofing. My long-term plan for connector lifetimes and
> > the connector list is:
> > - refcounting for connectors (Dave has wip patches already).
> > - separate lock for the connector list (and only that).
> > 
> > Doing it entirely separate would make things easier and more robust.
> 
> Ok makes sense.
> 
> > I merged patch 1 meanwhile to drm-misc.
> 
> So may I re-send only patches 2-4 then (using "drm-misc" as a base)?

Sure. drm-misc is also in linux-next, in case you need other bits to be
able to test all your patches.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch