Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751285AbdGQGzI (ORCPT ); Mon, 17 Jul 2017 02:55:08 -0400 Received: from mail.free-electrons.com ([62.4.15.54]:39598 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751256AbdGQGzG (ORCPT ); Mon, 17 Jul 2017 02:55:06 -0400 Date: Mon, 17 Jul 2017 08:55:04 +0200 From: Maxime Ripard To: Chen-Yu Tsai Cc: Daniel Vetter , David Airlie , Jani Nikula , Sean Paul , Inki Dae , Joonyoung Shim , Seung-Woo Kim , Kyungmin Park , Kukjin Kim , Krzysztof Kozlowski , Laurent Pinchart , Mark Yao , Heiko Stuebner , dri-devel , linux-kernel , linux-arm-kernel , "moderated list:ARM/SAMSUNG EXYNO..." , "open list:ARM/SHMOBILE ARM..." , "open list:ARM/Rockchip SoC..." Subject: Re: [PATCH 4/4] drm/sun4i: make sure we don't have a commit pending Message-ID: <20170717065504.xnahsboer3fh4k3i@flea> References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="yyvplvvq5lnu33e5" Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2151 Lines: 59 --yyvplvvq5lnu33e5 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jul 14, 2017 at 04:56:01PM +0800, Chen-Yu Tsai wrote: > Hi, >=20 > On Thu, Jul 13, 2017 at 10:41 PM, Maxime Ripard > wrote: > > In the earlier display engine designs, any register access while a comm= it > > is pending is forbidden. > > > > One of the symptoms is that reading a register will return another, ran= dom, > > register value which can lead to register corruptions if we ever do a > > read/modify/write cycle. >=20 > Alternatively, if changes to the backend (layers) are guaranteed to happen > while the CRTC is disabled (which seems to be the case after looking at > drm_atomic_helper_commit_planes and drm_atomic_helper_commit_tail), we > could just turn on register auto-commit all the time and not deal with > this. As far as I understand, it will only be the case if we need a new modeset or we changed the active CRTC or connectors. But if you change only the format, buffers or properties it won't be the case, and we'll need to commit. Maxime --=20 Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com --yyvplvvq5lnu33e5 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJZbF9IAAoJEBx+YmzsjxAgitcP/AzVUYWQ/7YwScIi3w1+1y3C NmHrSmtqH2cKCgft+K5IkbxcLNre8jaVprbTSPPuUjfz4wxyLiz1/rgmSbAt5oeE WX9TrebgCLpnwQMiaHC2qRqIaJXHjab5h4gFRI9x8ghzX8ozqnzG8brknqaRjn5b aHVkf4gjJ2NS75CJxNxjPoWDdbCX1+6fepPlHcBwhq+NvcMbBehybXuVQ+cktx9O RE3ZxixHEZZFmtdc+4Laq93XcMrmEkZRimwyWs641xF5BwPtbipZpbY7lEV4+1r5 pZNSM+rZH9opaGntT10fvwTfgSnu+dcRd65ZsECNzLPmKUjWzEn7yVKgqhTDwPtX I4FdtbW7mUnpdrIM9jPnYrvoxbcsCbebR3dPuwl8xtpqVQGGYdOBK/9lbTSuP38D kLg/wIeZ8K/1EoYWZyhESWtw50Joqi2xjipxApmXgYjTa+PVfjo/+ywU9KrQspPQ XhCkWAjJzXkuMBh3WR0n0DwmiAQ/TqklJBiIGmXH0O0ARbP3CkCBMB/FQ3plrLg7 bZxu/kieLSuxV5K2K6dNzoQJe/0rYHl76fr1kTUS7j8EE5d0GO1u/dY22eJ9y0je AAeBSUdJ3ybyJptbeEf4yxggkkuY9lMKpJ5edrDQoP2/HF+0MEfaCWNINnLXlFl9 xsGcpQYVCFY91+GVpsdt =2/Xt -----END PGP SIGNATURE----- --yyvplvvq5lnu33e5--