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[209.85.219.170]) by smtp.gmail.com with ESMTPSA id c29sm357707qtv.93.2021.04.28.09.45.26 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Apr 2021 09:45:27 -0700 (PDT) Received: by mail-yb1-f170.google.com with SMTP id s9so16394032ybe.5 for ; Wed, 28 Apr 2021 09:45:26 -0700 (PDT) X-Received: by 2002:a25:7157:: with SMTP id m84mr42521872ybc.175.1619628324558; Wed, 28 Apr 2021 09:45:24 -0700 (PDT) MIME-Version: 1.0 References: <20210423165906.2504169-1-dianders@chromium.org> <20210423095743.v5.17.Ibd31b8f7c73255d68c5c9f5b611b4bfaa036f727@changeid> In-Reply-To: <20210423095743.v5.17.Ibd31b8f7c73255d68c5c9f5b611b4bfaa036f727@changeid> From: Sean Paul Date: Wed, 28 Apr 2021 12:44:45 -0400 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5 17/20] drm/panel: panel-simple: Power the panel when reading the EDID To: Douglas Anderson Cc: Andrzej Hajda , Neil Armstrong , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Sam Ravnborg , Wolfram Sang , robdclark@chromium.org, dri-devel , David Airlie , linux-arm-msm , Steev Klimaszewski , Stephen Boyd , Stanislav Lisovskiy , Thierry Reding , linux-i2c@vger.kernel.org, Bjorn Andersson , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Fri, Apr 23, 2021 at 1:00 PM Douglas Anderson wrote: > > I don't believe that it ever makes sense to read the EDID when a panel > is not powered and the powering on of the panel is the job of > prepare(). Let's make sure that this happens before we try to read the > EDID. We use the pm_runtime functions directly rather than directly > calling the normal prepare() function because the pm_runtime functions > are definitely refcounted whereas it's less clear if the prepare() one > is. > > NOTE: I'm not 100% sure how EDID reading was working for folks in the > past, but I can only assume that it was failing on the initial attempt > and then working only later. This patch, presumably, will fix that. If > some panel out there really can read the EDID without powering up and > it's a big advantage to preserve the old behavior we can add a > per-panel flag. It appears that providing the DDC bus to the panel in > the past was somewhat uncommon in any case. > Maybe some combination of drivers caching the EDID for panels while they're already powered and overly broad pm runtime references? At any rate, this makes sense to me, Reviewed-by: Sean Paul > Signed-off-by: Douglas Anderson > Reviewed-by: Bjorn Andersson > --- > > (no changes since v1) > > drivers/gpu/drm/panel/panel-simple.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c > index 4de33c929a59..a12dfe8b8d90 100644 > --- a/drivers/gpu/drm/panel/panel-simple.c > +++ b/drivers/gpu/drm/panel/panel-simple.c > @@ -510,12 +510,18 @@ static int panel_simple_get_modes(struct drm_panel *panel, > > /* probe EDID if a DDC bus is available */ > if (p->ddc) { > - struct edid *edid = drm_get_edid(connector, p->ddc); > + struct edid *edid; > > + pm_runtime_get_sync(panel->dev); > + > + edid = drm_get_edid(connector, p->ddc); > if (edid) { > num += drm_add_edid_modes(connector, edid); > kfree(edid); > } > + > + pm_runtime_mark_last_busy(panel->dev); > + pm_runtime_put_autosuspend(panel->dev); > } > > /* add hard-coded panel modes */ > -- > 2.31.1.498.g6c1eba8ee3d-goog > > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel