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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gjmS9-0000Mp-FN; Wed, 16 Jan 2019 14:46:01 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gjmS6-0000Gw-OR for linux-arm-kernel@lists.infradead.org; Wed, 16 Jan 2019 14:46:00 +0000 Received: from bbrezillon (91-160-177-164.subs.proxad.net [91.160.177.164]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8F72520657; Wed, 16 Jan 2019 14:45:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547649958; bh=RpxCb7uIWRRnSDY18jtHaRcDC4JxCs48Xtr9FHci1pA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=cR/DhM8fX69O18yQo6C4R4q1WzitweTNFkCofTQiA4aGLy0Gh18x97b+adlHkewQc 3/WLhtWa1yHvP9aYeMhMrcitAgof465jSeVxkHx+Ttnq/1Uh0imMB1TUPA9WOzKdD7 9Bh3ON1HQnPneSShoSJvkq5VvDEPvqlID4TKgMiY= Date: Wed, 16 Jan 2019 15:45:47 +0100 From: Boris Brezillon To: Peter Rosin Subject: Re: [PATCH 4/4] drm/atmel-hlcdc: do not immediately disable planes, wait for next frame Message-ID: <20190116154547.711d7087@bbrezillon> In-Reply-To: References: <20190110151020.30468-1-peda@axentia.se> <20190110151020.30468-5-peda@axentia.se> <20190110182904.5efd08f2@bbrezillon> <20190110202522.10206f2d@bbrezillon> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190116_064558_846319_44AE5F24 X-CRM114-Status: GOOD ( 24.31 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexandre Belloni , David Airlie , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Boris Brezillon , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 11 Jan 2019 14:29:28 +0000 Peter Rosin wrote: > On 2019-01-10 20:25, Boris Brezillon wrote: > > On Thu, 10 Jan 2019 18:51:21 +0000 > > Peter Rosin wrote: > > > >> On 2019-01-10 18:29, Boris Brezillon wrote: > >>> On Thu, 10 Jan 2019 15:10:48 +0000 > >>> Peter Rosin 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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel