[Nouveau] [PATCH 9/9] drm: Turn off crtc before tearing down its data structure

[Lukas Wunner]

On Wed, Jun 01, 2016 at 04:40:12PM +0200, Daniel Vetter wrote:
> On Wed, Jun 01, 2016 at 02:36:41PM +0200, Lukas Wunner wrote:
> > On Wed, May 25, 2016 at 03:43:42PM +0200, Daniel Vetter wrote:
> > > On Wed, May 25, 2016 at 12:51 PM, Lukas Wunner <lukas at wunner.de> wrote:
> > > > On Tue, May 24, 2016 at 11:30:42PM +0200, Daniel Vetter wrote:
> > > > > On Tue, May 24, 2016 at 06:03:27PM +0200, Lukas Wunner wrote:
> > > > > > When a drm_crtc structure is destroyed with drm_crtc_cleanup(), the DRM
> > > > > > core does not turn off the crtc first and neither do the drivers. With
> > > > > > nouveau, radeon and amdgpu, this causes a runtime pm ref to be leaked on
> > > > > > driver unload if at least one crtc was enabled.
> > > > > >
> > > > > > (See usage of have_disp_power_ref in nouveau_crtc_set_config(),
> > > > > > radeon_crtc_set_config() and amdgpu_crtc_set_config()).
> > > > > >
> > > > > > Fixes: 5addcf0a5f0f ("nouveau: add runtime PM support (v0.9)")
> > > > > > Cc: Dave Airlie <airlied at redhat.com>
> > > > > > Tested-by: Karol Herbst <nouveau at karolherbst.de>
> > > > > > Signed-off-by: Lukas Wunner <lukas at wunner.de>
> > > 
> > > With legacy kms the only way to keep a crtc enabled is to display a
> > > drm_framebuffer on it. And drm_mode_config_cleanup has a WARN_ON if
> > > framebuffers are left behind. There's a bunch of options:
> > > - nouveau somehow manages to keep the crtc on without a framebuffer
> > > - nouveau somehow leaks a drm_framebuffer, but removes it from the fb_list
> > > - something else
> > 
> > Found it. nouveau_fbcon_destroy() doesn't call drm_framebuffer_remove().
> > If I add that, the crtc gets properly disabled on unload.
> > 
> > It does call drm_framebuffer_cleanup(). That's why there was no WARN,
> > drm_mode_config_cleanup() only WARNs if a framebuffer was left on the
> > mode_config.fb_list.
> > 
> > radeon and amdgpu have the same problem. In fact there are very few
> > drivers that call drm_framebuffer_remove(): tegra, msm, exynos, omapdrm
> > and i915 (since Imre Deak's 9d6612516da0).
> > 
> > Should we add a WARN to prevent this? How about WARN_ON(crtc->enabled)
> > in drm_crtc_cleanup()?
> > 
> > Also, i915 calls drm_framebuffer_unregister_private() before it calls
> > drm_framebuffer_remove(). This ordering has the unfortunate side effect
> > that the drm_framebuffer has ID 0 in log messages emitted by
> > drm_framebuffer_remove():
> > 
> > [   39.680874] [drm:drm_mode_object_unreference] OBJ ID: 0 (3)
> > [   39.680878] [drm:drm_mode_object_unreference] OBJ ID: 0 (2)
> > [   39.680884] [drm:drm_mode_object_unreference] OBJ ID: 0 (1)
> 
> Well we must first unregister it before we can remove it, so this is
> unavoidable.

Yes but drm_framebuffer_free() calls drm_mode_object_unregister()
and is invoked by drm_framebuffer_remove(), so the additional call to
drm_framebuffer_unregister_private() in intel_fbdev_destroy() seems
superfluous. Or is there some reason I'm missing that this needs to
be called before intel_unpin_fb_obj()?


> Wrt switching from _cleanup to _remove, iirc there was troubles with the
> later calling into the fb->funcs->destroy hook. But many drivers have
> their fbdev fb embedded into some struct (instead of a pointer like i915),
> and then things go sideways badly. That's why you can't just blindly
> replace them.

So the options seem to be:

(1) Refactor nouveau, radeon and amdgpu to not embed their framebuffer
    struct in their fbdev struct, so that drm_framebuffer_remove() can
    be used.

(2) Amend each of them to turn off crtcs which are using the fbdev
    framebuffer, duplicating the code in drm_framebuffer_remove().

(3) Split drm_framebuffer_remove(), move the portion to turn off crtcs
    into a separate helper, say, drm_framebuffer_deactivate(), call that
    from nouveau, radeon and amdgpu.

(4) Go back to square one and use patch [9/9] of this series.

Which one would be most preferred? Is there another solution I've missed?

Thanks,

Lukas