Re: [PATCH 3/4] drm: Only lastclose on unload for legacy drivers

From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Alex Deucher <alexdeucher@gmail.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 3/4] drm: Only lastclose on unload for legacy drivers
Date: Thu, 3 Aug 2017 15:54:34 +0200	[thread overview]
Message-ID: <CAKMK7uG2XNYk-7uc0Rf27SseKcknCXeqL-RRdajCDeX5ceQ4+Q@mail.gmail.com> (raw)
In-Reply-To: <CAKMK7uH7sirxfNKV9FAOJS23QHMrniSQ-5yX72V_N9uCfH947w@mail.gmail.com>

On Thu, Aug 3, 2017 at 1:17 AM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> On Wed, Aug 2, 2017 at 10:50 PM, Alex Deucher <alexdeucher@gmail.com> wrote:
>> On Wed, Aug 2, 2017 at 7:56 AM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>>> The only thing modern drivers are supposed to do in lastclose is
>>> restore the fb emulation state. Which is entirely optional, and
>>> there's really no reason to do that. So restrict it to legacy drivers
>>> (where the driver cleanup essentially happens in lastclose).
>>
>> vga_switcheroo_process_delayed_switch() gets called in lastclose.
>> Won't that need to get moved elsewhere for this to work?
>
> Hm right, I forgot the lazy way to do runtime pm by keeping the device
> alive as long as anyone has an open fd for it ... This shouldn't be a
> problem, since you need to unregister from vgaswitcheroo anyway on
> unload. Maybe that blows up, I'll check the code and augment the patch
> as needed.

So I think there's 3 cases:
- Trying to unload the module. You can't do that while anyone has the
fd still open, so lastclose is guaranteeed to run.
- Forcefully unbinding the driver through sysfs. Not any better, since
the can_switch stuff checks for the open count, and so will delay the
delayed switch no matter what.
- Actual hotremoval: a) not implemented since none of the drivers
taking part in vgaswitcheroo correctly unplug the drm device and b)
you can't hotremove a chip from a laptop.

So I think I'm not breaking this anymore than it probably already is :-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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