diff mbox series

[v5,17/20] drm/panel: panel-simple: Power the panel when reading the EDID

Message ID 20210423095743.v5.17.Ibd31b8f7c73255d68c5c9f5b611b4bfaa036f727@changeid
State Superseded
Headers show
Series drm: Fix EDID reading on ti-sn65dsi86; solve some chicken-and-egg problems | expand

Commit Message

Doug Anderson April 23, 2021, 4:59 p.m. UTC 
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.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---

(no changes since v1)

 drivers/gpu/drm/panel/panel-simple.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Comments

Sean Paul April 28, 2021, 4:44 p.m. UTC | #1 
On Fri, Apr 23, 2021 at 1:00 PM Douglas Anderson <dianders@chromium.org> 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 <seanpaul@chromium.org>

> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> ---
>
> (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
diff mbox series

Patch

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 */