Re: [PATCH] drm/i2c: tda998x: don't register the connector

From: Brian Starkey
Date: Fri Sep 23 2016 - 08:53:05 EST

On Fri, Sep 23, 2016 at 12:58:46PM +0200, Daniel Vetter wrote:
On Fri, Sep 23, 2016 at 11:34 AM, Liviu Dudau <Liviu.Dudau@xxxxxxx> wrote:
rmmod-ing the hdlcd module generates a WARN() splat as the vsync is still
enabled, but we never got the call to turn off the CRTC. Brian is still
tracking through the fbdev emulation to figure out the cause for that.

fbdev emulation doesn't do that for you. If you need/want to shut down
all the crtcs on driver unload, you need to do that yourself. There's
atomic helpers to do that for you that for you.

The problem is a sort-of circular dependency between ->lastclose (at
least the common implementation of it), unregister and disabling

I want to move drm_dev_unregister() to be the first thing we do at
rmmod-time. However we need to disable fbdev first, otherwise
->lastclose restores the fbdev mode, guaranteeing that vsync is turned
on for drm_vsync_cleanup() to then WARN on.

There's a slightly different (perceived) problem - the one that Liviu
mentions - that drm_fbdev_cma_fini() doesn't disable the CRTC anyway.
You say it's not the fbdev helpers' responsibility to teardown their
modeset, but regardless I have nowhere to disable the CRTC if I want
to do drm_dev_unregister() first; and if the CRTC isn't disabled
there's always a chance of hitting the same vsync WARN even without

We *could* add an ->unload and disable everything there, but as that's
deprecated I'm guessing there should be another way.
Perhaps we should track ->firstopen/->lastclose pairs so we can detect
that ->lastclose is being called from unregister and use it to
disable everything in that case.

drm_vblank_cleanup() seems to have been carried over to unregister
from drm_put_dev(), but drm_dev_register() doesn't call
drm_vblank_init() so it seems a little strange to have it there.
I can see other drivers I'd expect to hit the same WARN but I don't
have HW to test it on.


Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 -