From: Boris Brezillon <bbrezillon@kernel.org>
To: Peter Rosin <peda@axentia.se>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
David Airlie <airlied@linux.ie>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Boris Brezillon <boris.brezillon@bootlin.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 4/4] drm/atmel-hlcdc: do not immediately disable planes, wait for next frame
Date: Wed, 16 Jan 2019 15:45:47 +0100 [thread overview]
Message-ID: <20190116154547.711d7087@bbrezillon> (raw)
In-Reply-To: <e35d6894-fd62-efd1-38f7-cc5cbdbbacbb@axentia.se>
On Fri, 11 Jan 2019 14:29:28 +0000
Peter Rosin <peda@axentia.se> wrote:
> On 2019-01-10 20:25, Boris Brezillon wrote:
> > On Thu, 10 Jan 2019 18:51:21 +0000
> > Peter Rosin <peda@axentia.se> wrote:
> >
> >> On 2019-01-10 18:29, Boris Brezillon wrote:
> >>> On Thu, 10 Jan 2019 15:10:48 +0000
> >>> Peter Rosin <peda@axentia.se> wrote:
> >>>
> >>>> The A2Q and UPDATE bits have no effect in the channel disable registers.
> >>>> However, since they are present, assume that the intention is to disable
> >>>> planes, not immediately as indicated by the RST bit, but on the next
> >>>> frame shift since that is what A2Q and UPDATE means in the channel enable
> >>>> registers.
> >>>>
> >>>> Disabling the plane on the next frame shift is done with the EN bit,
> >>>> so use that.
> >>>
> >>> It's been a long time, but I think I had a good reason for forcing a
> >>> reset. IIRC, when you don't do that and the CRTC is disabled before the
> >>> plane, the EN bit stays around, and next time you queue a plane update,
> >>> you'll start with an invalid buf pointer.
> >>
> >> It might be possible to clear the EN bit in ...CHDR before enabling the
> >> plane in ...CHER. Or is that too late?
> >
> > I think I tried that, but I'm not sure (BTW, this change was done in
> > bd4248bb5e8b ("drm: atmel-hlcdc: reset layer A2Q and UPDATE bits when
>
> That patch is a big fat NOP if you read the documentation. Those bits
> are marked with a '-' for all LCDC channel disable registers, for all
> supported chips IIUC. Are the effects of those bits mentioned in any
> errata?
IIRC, it was not documented in the datasheet, but this came out during
a discussion with the IP designer.
>
> It would be good with a comment that the present undocumented disable
> method is intentional.
Yes, I should have added a comment about that, my bad.
> That would have kept me from assuming the whole
> thing was just copy-paste junk from ..._enable that happened to work.
>
> >> disabling it")). Anyway, I'm not even sure this is still needed now
> >> that atomic updates have a wait_for_flip_done/vblank() in the commit
> >> path.
>
> The documentation for the RST bit states "Resets the layer immediately.
> The frame is aborted." which sounds a bit scary and heavy-handed. But
> again, I don't know what that actually means and what the effects are
> but that was the reason for me wanting to avoid the RST bit.
As I said, I'm not even sure the problem I was trying to fix still
exists.
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next prev parent reply other threads:[~2019-01-16 14:46 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-10 15:10 [PATCH 0/4] drm/atmel-hlcdc: fix plane clipping/rotation issues Peter Rosin
2019-01-10 15:10 ` [PATCH 1/4] drm/atmel-hlcdc: rotate planes counterclockwise Peter Rosin
2019-01-10 15:10 ` [PATCH 2/4] drm/atmel-hlcdc: do not swap w/h of the crtc when a plane is rotated Peter Rosin
2019-01-10 17:48 ` Boris Brezillon
2019-01-11 13:29 ` Peter Rosin
2019-01-11 14:14 ` Nicolas.Ferre
2019-01-10 15:10 ` [PATCH 3/4] drm/atmel-hlcdc: fix clipping of planes Peter Rosin
2019-01-10 15:10 ` [PATCH 4/4] drm/atmel-hlcdc: do not immediately disable planes, wait for next frame Peter Rosin
2019-01-10 17:29 ` Boris Brezillon
2019-01-10 18:51 ` Peter Rosin
2019-01-10 19:25 ` Boris Brezillon
2019-01-11 14:29 ` Peter Rosin
2019-01-16 14:45 ` Boris Brezillon [this message]
2019-01-10 17:45 ` [PATCH 0/4] drm/atmel-hlcdc: fix plane clipping/rotation issues Boris Brezillon
2019-01-10 20:16 ` Sam Ravnborg
2019-01-11 9:16 ` Peter Rosin
2019-01-10 21:24 ` Peter Rosin
2019-01-11 14:18 ` Nicolas.Ferre
2019-01-27 8:27 ` Boris Brezillon
2019-01-31 13:13 ` Peter Rosin
2019-01-31 13:21 ` Boris Brezillon
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