linux-kernel - Re: [PATCH] drm/exynos: fix vblank handling during dpms off

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Message-ID: <20141009085258.GI5182@n2100.arm.linux.org.uk>
Date:	Thu, 9 Oct 2014 09:52:58 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Andrzej Hajda <a.hajda@...sung.com>,
	Inki Dae <inki.dae@...sung.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Thierry Reding <treding@...dia.com>,
	linux-samsung-soc@...r.kernel.org,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Seung-Woo Kim <sw0312.kim@...sung.com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Benjamin Gaignard <benjamin.gaignard@...aro.org>,
	Ville Syrjälä 
	<ville.syrjala@...ux.intel.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] drm/exynos: fix vblank handling during dpms off

On Thu, Oct 09, 2014 at 02:43:02PM +0900, Alexandre Courbot wrote:
> But there might be another issue, which is that calls to  
> drm_vblank_get() will return -EINVAL if invoked between drm_blank_off  
> and drm_blank_on. Is this really the desired behavior? Can it at least  
> happen? If so, how are drivers supposed to react to this situation?

I've not yet seen the commit which causes this problem, but I hope
that drm_wait_vblank() isn't affected by this.  In current mainline,
drm_vblank_get() is used inside drm_wait_vblank(), which is called as
a result of userspace calling DRM_IOCTL_WAIT_VBLANK.

So, what is the effect of this change on user applications making use
of the vblank wait ioctl - and is that change intended?

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