Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752677AbdGNI42 (ORCPT ); Fri, 14 Jul 2017 04:56:28 -0400 Received: from smtp.csie.ntu.edu.tw ([140.112.30.61]:49972 "EHLO smtp.csie.ntu.edu.tw" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751340AbdGNI40 (ORCPT ); Fri, 14 Jul 2017 04:56:26 -0400 MIME-Version: 1.0 In-Reply-To: References: From: Chen-Yu Tsai Date: Fri, 14 Jul 2017 16:56:01 +0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 4/4] drm/sun4i: make sure we don't have a commit pending To: Maxime Ripard 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 , Chen-Yu Tsai , dri-devel , linux-kernel , linux-arm-kernel , "moderated list:ARM/SAMSUNG EXYNO..." , "open list:ARM/SHMOBILE ARM..." , "open list:ARM/Rockchip SoC..." Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3012 Lines: 72 Hi, On Thu, Jul 13, 2017 at 10:41 PM, Maxime Ripard wrote: > In the earlier display engine designs, any register access while a commit > is pending is forbidden. > > One of the symptoms is that reading a register will return another, random, > register value which can lead to register corruptions if we ever do a > read/modify/write cycle. 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. ChenYu > > Signed-off-by: Maxime Ripard > --- > drivers/gpu/drm/sun4i/sun4i_backend.c | 14 ++++++++++++++ > drivers/gpu/drm/sun4i/sun4i_crtc.c | 1 + > 2 files changed, 15 insertions(+) > > diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c > index cf480218daa5..ce1f40f7511e 100644 > --- a/drivers/gpu/drm/sun4i/sun4i_backend.c > +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c > @@ -67,6 +67,19 @@ static void sun4i_backend_commit(struct sunxi_engine *engine) > SUN4I_BACKEND_REGBUFFCTL_LOADCTL); > } > > +static int sun4i_backend_commit_poll(struct sunxi_engine *engine) > +{ > + u32 val; > + > + DRM_DEBUG_DRIVER("Polling for the commit to end\n"); > + > + return regmap_read_poll_timeout(engine->regs, > + SUN4I_BACKEND_REGBUFFCTL_REG, > + val, > + !(val & SUN4I_BACKEND_REGBUFFCTL_LOADCTL), > + 100, 50000); > +} > + > void sun4i_backend_layer_enable(struct sun4i_backend *backend, > int layer, bool enable) > { > @@ -330,6 +343,7 @@ static int sun4i_backend_of_get_id(struct device_node *node) > > static const struct sunxi_engine_ops sun4i_backend_engine_ops = { > .commit = sun4i_backend_commit, > + .commit_poll = sun4i_backend_commit_poll, > .layers_init = sun4i_layers_init, > .apply_color_correction = sun4i_backend_apply_color_correction, > .disable_color_correction = sun4i_backend_disable_color_correction, > diff --git a/drivers/gpu/drm/sun4i/sun4i_crtc.c b/drivers/gpu/drm/sun4i/sun4i_crtc.c > index 2eba1d8639d8..31550493fa1d 100644 > --- a/drivers/gpu/drm/sun4i/sun4i_crtc.c > +++ b/drivers/gpu/drm/sun4i/sun4i_crtc.c > @@ -34,6 +34,7 @@ static void sun4i_crtc_atomic_begin(struct drm_crtc *crtc, > struct drm_crtc_state *old_state) > { > struct sun4i_crtc *scrtc = drm_crtc_to_sun4i_crtc(crtc); > + struct sunxi_engine *engine = scrtc->engine; > struct drm_device *dev = crtc->dev; > unsigned long flags; > > -- > git-series 0.9.1