Re: [Intel-gfx] [RFC v2 1/4] drm: Add support to find drm_panel by name

From: Thierry Reding <thierry.reding@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Jani Nikula <jani.nikula@intel.com>,
	Shobhit Kumar <shobhit.kumar@intel.com>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Andrzej Hajda <a.hajda@samsung.com>,
	jacob.jun.pan@intel.com, Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [Intel-gfx] [RFC v2 1/4] drm: Add support to find drm_panel by name
Date: Fri, 16 Jan 2015 13:19:04 +0100	[thread overview]
Message-ID: <20150116121902.GE4885@ulmo.nvidia.com> (raw)
In-Reply-To: <CAKMK7uH4DRL+S5agmt-sUcdx=Uk9=73LmDdTVWkFy_9Qcu2ouA@mail.gmail.com>

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On Tue, Jan 13, 2015 at 12:08:11AM +0100, Daniel Vetter wrote:
> On Fri, Jan 9, 2015 at 1:50 PM, Jani Nikula <jani.nikula@intel.com> wrote:
> > I have a slightly uneasy feeling about handing out drm_panel pointers
> > (both from here and of_drm_find_panel) without refcounting. If the panel
> > driver gets removed, whoever called the find functions will have a
> > dangling pointer. I supposed this will be discussed on drm-devel.
> 
> There's been some discussion already about exactly this problem (but
> with drm bridges) with Thierry and some other people. Cc'ed them all
> hopefully. Especially when the panel/bridge is a separate driver
> there's imo indeed an issue.

I posted patches some time ago to create a generic registry to do the
actual ref-counting[0]. It didn't seem to be very well received by Greg
for the core, so perhaps we could test-drive it in DRM first for panels
and bridges and once it's matured a bit it could still be promoted to
the driver core, or maybe lib/.

The difficult part about it is that while reference counting gives you
the benefit of keeping a valid pointer around, you may still want to
have a method of getting notified of the panel going away. I've thought
a bit about that and I think we could probably integrate that into the
registry, since that will notice anyway.

Thierry

[0]: http://www.spinics.net/linux/lists/kernel/msg1859333.html

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