[v5,18/20] drm/panel: panel-simple: Cache the EDID as long as we retain power

Message ID 20210423095743.v5.18.If050957eaa85cf45b10bcf61e6f7fa61c9750ebf@changeid
State Accepted
Commit 63358e24ee79e8f43dadb755cbe8e955230c03a1
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Series
  • drm: Fix EDID reading on ti-sn65dsi86; solve some chicken-and-egg problems
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Commit Message

Doug Anderson April 23, 2021, 4:59 p.m.
It doesn't make sense to go out to the bus and read the EDID over and
over again. Let's cache it and throw away the cache when we turn power
off from the panel. Autosuspend means that even if there are several
calls to read the EDID before we officially turn the power on then we
should get good use out of this cache.

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 | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

Comments

Sean Paul April 28, 2021, 4:50 p.m. | #1
On Fri, Apr 23, 2021 at 1:00 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> It doesn't make sense to go out to the bus and read the EDID over and
> over again. Let's cache it and throw away the cache when we turn power
> off from the panel. Autosuspend means that even if there are several
> calls to read the EDID before we officially turn the power on then we
> should get good use out of this cache.
>

I think i915 caches the edid once on init and never refreshes it
(assuming no hotplugs). That said, I think it makes sense for a more
conservative approach in panel-simple.


> 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 | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index a12dfe8b8d90..9be050ab372f 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -189,6 +189,8 @@ struct panel_simple {
>         struct gpio_desc *enable_gpio;
>         struct gpio_desc *hpd_gpio;
>
> +       struct edid *edid;
> +
>         struct drm_display_mode override_mode;
>
>         enum drm_panel_orientation orientation;
> @@ -345,6 +347,9 @@ static int panel_simple_suspend(struct device *dev)
>         regulator_disable(p->supply);
>         p->unprepared_time = ktime_get();
>
> +       kfree(p->edid);
> +       p->edid = NULL;
> +
>         return 0;
>  }
>
> @@ -510,15 +515,13 @@ static int panel_simple_get_modes(struct drm_panel *panel,
>
>         /* probe EDID if a DDC bus is available */
>         if (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);
> -               }
> +               if (!p->edid)
> +                       p->edid = drm_get_edid(connector, p->ddc);
> +
> +               if (p->edid)
> +                       num += drm_add_edid_modes(connector, p->edid);

I suppose this would keep banging on the ddc if drm_get_edid()
continuously returns NULL, but maybe that's desireable (it'll succeed
sometime in the future)? At any rate, this is an improvement on
current behavior so it has my vote.

Reviewed-by: Sean Paul <seanpaul@chromium.org>

>
>                 pm_runtime_mark_last_busy(panel->dev);
>                 pm_runtime_put_autosuspend(panel->dev);
> --
> 2.31.1.498.g6c1eba8ee3d-goog
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

Patch

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index a12dfe8b8d90..9be050ab372f 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -189,6 +189,8 @@  struct panel_simple {
 	struct gpio_desc *enable_gpio;
 	struct gpio_desc *hpd_gpio;
 
+	struct edid *edid;
+
 	struct drm_display_mode override_mode;
 
 	enum drm_panel_orientation orientation;
@@ -345,6 +347,9 @@  static int panel_simple_suspend(struct device *dev)
 	regulator_disable(p->supply);
 	p->unprepared_time = ktime_get();
 
+	kfree(p->edid);
+	p->edid = NULL;
+
 	return 0;
 }
 
@@ -510,15 +515,13 @@  static int panel_simple_get_modes(struct drm_panel *panel,
 
 	/* probe EDID if a DDC bus is available */
 	if (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);
-		}
+		if (!p->edid)
+			p->edid = drm_get_edid(connector, p->ddc);
+
+		if (p->edid)
+			num += drm_add_edid_modes(connector, p->edid);
 
 		pm_runtime_mark_last_busy(panel->dev);
 		pm_runtime_put_autosuspend(panel->dev);