Re: [PATCH 00/19] drm: debugfs: Remove all files automatically on cleanup

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Jan 30, 2017 at 10:03:44AM +0100, Daniel Vetter wrote:
> On Mon, Jan 30, 2017 at 09:58:48AM +0100, Thierry Reding wrote:
> > On Fri, Jan 27, 2017 at 03:05:46PM +0100, Daniel Vetter wrote:
> > > On Fri, Jan 27, 2017 at 10:36:16AM +0100, Thierry Reding wrote:
> > > > On Fri, Jan 27, 2017 at 08:49:34AM +0100, Daniel Vetter wrote:
> > > > > On Thu, Jan 26, 2017 at 11:56:02PM +0100, Noralf Trønnes wrote:
> > > > > > This patchset removes the need for drivers to clean up their debugfs
> > > > > > files on exit. It is done automatically in drm_debugfs_cleanup().
> > > > > > This funtion is also called should the driver error out in it's
> > > > > > drm_driver.debugfs_init callback.
> > > > > > 
> > > > > > Two drivers still use drm_debugfs_remove_files():
> > > > > > - tegra in it's connectors, not sure if I can remove it.
> > > > > 
> > > > > I read through them, and they're removed on the component device nodes
> > > > > stuff. That looks somewhat fishy from a lifetime point of view, and I
> > > > > think removing all that code would be better, too.
> > > > 
> > > > What makes you think that's problematic from a lifetime point of view?
> > > > The component device is tied to the DRM device, so these callbacks are
> > > > called at the right time.
> > > 
> > > debugfs is a userspace interface, which should disappear when
> > > drm_dev_unregister gets called. I'm not sure at all whether that lines up
> > > with the cleanup of all your component nodes, but otoh it's rather
> > > academic since you can't hotplug a tegra.
> > > 
> > > > That said, I think it's safe to remove the other debugfs files from
> > > > Tegra. It might not be possible to remove the cleanup functions
> > > > altogether, though, because they have to do a special dance involving
> > > > kmemdup() drm_debugfs_create_files() and kfree() in order to support
> > > > debugfs files for multiple instances of subdevices.
> > > 
> > > Hm, that entire "do debugfs on the minor" thing makes almost never sense.
> > > All the things we have left in modern drivers are either per-fd, or
> > > per-device. Nothing of interest is per-minor. Or do you mean something
> > > else?
> > 
> > I'm not sure I understand what you're saying. We have plenty of code
> > that adds debugfs files to the connector's debugfs entry. And that's
> > within the minor's debugfs root.
> > 
> > Am I missing something?
> 
> Per-connector entries are fine, per-minor imo not.

Most, if not all, debugfs files in Tegra a per-connector. We have a
couple that are per-CRTC. And then we have two files that are on the
minor, which is something I had copied from i915, if I remember
correctly, though I can't seem to find the original anymore. Maybe
that was moved somewhere else in the meantime?

> This is a historical accident, but it also doesn't really hurt anyone.
> I think it'd make much more sense to move everything into a
> per-devices entry (with maybe backwards compat links from minor to
> devices).

With per-device entries you mean rooted at the device backing the CRTC,
encoder, connector, ...?

> But really, this is 100% orthogonal to the cleanup here.

If we want to get rid of the remainder of the cleanup, then it's not
entirely orthogonal anymore. =)

Not to say that this cleanup isn't useful in its own right.

Thierry

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