linux-kernel - Re: drm: understanding the kernel warning during drm_vblank

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Message-ID: <20181129151928.GM9144@intel.com>
Date:   Thu, 29 Nov 2018 17:19:28 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Ahsan Hussain <ahsan_hussain@...tor.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: drm: understanding the kernel warning during drm_vblank_cleanup()

On Thu, Nov 29, 2018 at 07:30:45PM +0500, Ahsan Hussain wrote:
> Hi folks,
> 
> I'm new to DRM and trying to understand the warning in 
> drivers/gpu/drm/drm_vblank.c during drm_vblank_cleanup().
> 
> WARN_ON(READ_ONCE(vblank->enabled) &&
>      drm_core_check_feature(dev, DRIVER_MODESET));
> 
> Is the drm driver responsible for making sure that !(vblank->enabled) in 
> the .unbind operation, or is this something related to userspace? What 
> does the warning signify? Git history did not help here at all.

It signifies you haven't cleaned up things properly. Usually what
you would do is call drm_atomic_helper_shutdown() which will also
end up turnng vblank interrupts off, assuming you use
drm_vblank_on()/off() properly.

-- 
Ville Syrjälä
Intel