linux-kernel - Re: [PATCH 1/2] drm/atomic: Allow vblank-enabled + self-refresh "disable"

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Message-ID: <Y7hfRNHMjk5H+muj@phenom.ffwll.local>
Date:   Fri, 6 Jan 2023 18:49:56 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Brian Norris <briannorris@...omium.org>,
        Michel Dänzer <michel.daenzer@...lbox.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Sandy Huang <hjc@...k-chips.com>,
        linux-rockchip@...ts.infradead.org,
        Sean Paul <seanpaul@...omium.org>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/atomic: Allow vblank-enabled + self-refresh
 "disable"

On Fri, Jan 06, 2023 at 08:04:19AM +0100, Greg KH wrote:
> On Thu, Jan 05, 2023 at 05:40:17PM -0800, Brian Norris wrote:
> > The self-refresh helper framework overloads "disable" to sometimes mean
> > "go into self-refresh mode," and this mode activates automatically
> > (e.g., after some period of unchanging display output). In such cases,
> > the display pipe is still considered "on", and user-space is not aware
> > that we went into self-refresh mode. Thus, users may expect that
> > vblank-related features (such as DRM_IOCTL_WAIT_VBLANK) still work
> > properly.
> > 
> > However, we trigger the WARN_ONCE() here if a CRTC driver tries to leave
> > vblank enabled here.
> > 
> > Add a new exception, such that we allow CRTCs to be "disabled" (with
> > self-refresh active) with vblank interrupts still enabled.
> > 
> > Cc: <stable@...r.kernel.org> # dependency for subsequent patch
> 
> "subsequent" doesn't mean much when it is committed, give it a name
> perhaps?

It also looks a bit funny tbh, and a bit much like duct-tape. I need to
think through how this is supposed to work really.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch