[PATCH 0/9] drm/panel and i2c-hid: Allow panels and touchscreens to power sequence together

[PATCH 0/9] drm/panel and i2c-hid: Allow panels and touchscreens to power sequence together

[Douglas Anderson]

The big motivation for this patch series is mostly described in the patch
("drm/panel: Add a way for other devices to follow panel state"), but to
quickly summarize here: for touchscreens that are connected to a panel we
need the ability to power sequence the two device together. This is not a
new need, but so far we've managed to get by through a combination of
inefficiency, added costs, or perhaps just a little bit of brokenness.
It's time to do better. This patch series allows us to do better.

Assuming that people think this patch series looks OK, we'll have to
figure out the right way to land it. The panel patches and i2c-hid
patches will go through very different trees and so either we'll need
an Ack from one side or the other or someone to create a tag for the
other tree to pull in. This will _probably_ require the true drm-misc
maintainers to get involved, not a lowly committer. ;-)


Douglas Anderson (9):
  dt-bindings: HID: i2c-hid: Add "panel" property to i2c-hid backed
    panels
  drm/panel: Check for already prepared/enabled in drm_panel
  drm/panel: Add a way for other devices to follow panel state
  HID: i2c-hid: Switch to SYSTEM_SLEEP_PM_OPS()
  HID: i2c-hid: Rearrange probe() to power things up later
  HID: i2c-hid: Make suspend and resume into helper functions
  HID: i2c-hid: Support being a panel follower
  HID: i2c-hid: Do panel follower work on the system_wq
  arm64: dts: qcom: sc7180: Link trogdor touchscreens to the panels

 .../bindings/input/elan,ekth6915.yaml         |   6 +
 .../bindings/input/goodix,gt7375p.yaml        |   6 +
 .../bindings/input/hid-over-i2c.yaml          |   6 +
 .../boot/dts/qcom/sc7180-trogdor-coachz.dtsi  |   1 +
 .../dts/qcom/sc7180-trogdor-homestar.dtsi     |   1 +
 .../boot/dts/qcom/sc7180-trogdor-lazor.dtsi   |   1 +
 .../boot/dts/qcom/sc7180-trogdor-pompom.dtsi  |   1 +
 .../qcom/sc7180-trogdor-quackingstick.dtsi    |   1 +
 .../dts/qcom/sc7180-trogdor-wormdingler.dtsi  |   1 +
 drivers/gpu/drm/drm_panel.c                   | 194 +++++++++-
 drivers/hid/i2c-hid/i2c-hid-core.c            | 330 +++++++++++++-----
 include/drm/drm_panel.h                       |  89 +++++
 12 files changed, 542 insertions(+), 95 deletions(-)

-- 
2.40.1.698.g37aff9b760-goog

[PATCH 1/9] dt-bindings: HID: i2c-hid: Add "panel" property to i2c-hid backed panels

[Douglas Anderson]

As talked about in the patch ("drm/panel: Add a way for other devices
to follow panel state"), touchscreens that are connected to panels are
generally expected to be power sequenced together with the panel
they're attached to. Today, nothing provides information allowing you
to find out that a touchscreen is connected to a panel. Let's add a
phandle for this.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 Documentation/devicetree/bindings/input/elan,ekth6915.yaml  | 6 ++++++
 Documentation/devicetree/bindings/input/goodix,gt7375p.yaml | 6 ++++++
 Documentation/devicetree/bindings/input/hid-over-i2c.yaml   | 6 ++++++
 3 files changed, 18 insertions(+)

diff --git a/Documentation/devicetree/bindings/input/elan,ekth6915.yaml b/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
index 05e6f2df604c..d55b03bd3ec4 100644
--- a/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
+++ b/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
@@ -24,6 +24,12 @@ properties:
   interrupts:
     maxItems: 1
 
+  panel:
+    description: If this is a touchscreen, the panel it's connected to. This
+      indicates that the panel and touchscreen are expected to be power
+      sequenced together.
+    $ref: /schemas/types.yaml#/definitions/phandle
+
   reset-gpios:
     description: Reset GPIO; not all touchscreens using eKTH6915 hook this up.
 
diff --git a/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml b/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml
index ce18d7dadae2..a5cd8dafd450 100644
--- a/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml
+++ b/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml
@@ -30,6 +30,12 @@ properties:
   interrupts:
     maxItems: 1
 
+  panel:
+    description: If this is a touchscreen, the panel it's connected to. This
+      indicates that the panel and touchscreen are expected to be power
+      sequenced together.
+    $ref: /schemas/types.yaml#/definitions/phandle
+
   reset-gpios:
     true
 
diff --git a/Documentation/devicetree/bindings/input/hid-over-i2c.yaml b/Documentation/devicetree/bindings/input/hid-over-i2c.yaml
index 7156b08f7645..c7ea6c148838 100644
--- a/Documentation/devicetree/bindings/input/hid-over-i2c.yaml
+++ b/Documentation/devicetree/bindings/input/hid-over-i2c.yaml
@@ -44,6 +44,12 @@ properties:
     description: HID descriptor address
     $ref: /schemas/types.yaml#/definitions/uint32
 
+  panel:
+    description: If this is a touchscreen, the panel it's connected to. This
+      indicates that the panel and touchscreen are expected to be power
+      sequenced together.
+    $ref: /schemas/types.yaml#/definitions/phandle
+
   post-power-on-delay-ms:
     description: Time required by the device after enabling its regulators
       or powering it on, before it is ready for communication.
-- 
2.40.1.698.g37aff9b760-goog

Re: [PATCH 1/9] dt-bindings: HID: i2c-hid: Add "panel" property to i2c-hid backed panels

[Krzysztof Kozlowski]

On 23/05/2023 21:27, Douglas Anderson wrote:
> As talked about in the patch ("drm/panel: Add a way for other devices
> to follow panel state"), touchscreens that are connected to panels are
> generally expected to be power sequenced together with the panel
> they're attached to. Today, nothing provides information allowing you
> to find out that a touchscreen is connected to a panel. Let's add a
> phandle for this.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  Documentation/devicetree/bindings/input/elan,ekth6915.yaml  | 6 ++++++
>  Documentation/devicetree/bindings/input/goodix,gt7375p.yaml | 6 ++++++
>  Documentation/devicetree/bindings/input/hid-over-i2c.yaml   | 6 ++++++
>  3 files changed, 18 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/input/elan,ekth6915.yaml b/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
> index 05e6f2df604c..d55b03bd3ec4 100644
> --- a/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
> +++ b/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
> @@ -24,6 +24,12 @@ properties:
>    interrupts:
>      maxItems: 1
>  
> +  panel:
> +    description: If this is a touchscreen, the panel it's connected to. This

Hm, can there be different setup? Touchscreen without panel? What would
it be then?

Why only these touchscreens? This looks generic, so maybe in
touchscreen.yaml?

Best regards,
Krzysztof

Re: [PATCH 1/9] dt-bindings: HID: i2c-hid: Add "panel" property to i2c-hid backed panels

[Doug Anderson]

Hi,

On Tue, May 30, 2023 at 8:34 AM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 23/05/2023 21:27, Douglas Anderson wrote:
> > As talked about in the patch ("drm/panel: Add a way for other devices
> > to follow panel state"), touchscreens that are connected to panels are
> > generally expected to be power sequenced together with the panel
> > they're attached to. Today, nothing provides information allowing you
> > to find out that a touchscreen is connected to a panel. Let's add a
> > phandle for this.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> >  Documentation/devicetree/bindings/input/elan,ekth6915.yaml  | 6 ++++++
> >  Documentation/devicetree/bindings/input/goodix,gt7375p.yaml | 6 ++++++
> >  Documentation/devicetree/bindings/input/hid-over-i2c.yaml   | 6 ++++++
> >  3 files changed, 18 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/input/elan,ekth6915.yaml b/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
> > index 05e6f2df604c..d55b03bd3ec4 100644
> > --- a/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
> > +++ b/Documentation/devicetree/bindings/input/elan,ekth6915.yaml
> > @@ -24,6 +24,12 @@ properties:
> >    interrupts:
> >      maxItems: 1
> >
> > +  panel:
> > +    description: If this is a touchscreen, the panel it's connected to. This
>
> Hm, can there be different setup? Touchscreen without panel? What would
> it be then?

For a touchscreen that's a discrete device (not sharing logic / power
rails with the panel) you'd just leave off the panel node like we've
always done. Assuming folks like this series in general, I'll try to
improve the wording for v2.


> Why only these touchscreens? This looks generic, so maybe in
> touchscreen.yaml?

Ah, that makes sense. I guess we need to add an include of that file
from the elan and goodix bindings. The hid-over-i2c.yaml already has
it, though. I'm not 100% sure the existing "hid-over-i2c" driver in
Linux actually calls the function to parse all those properties, but I
guess that's a Linux problem and not a DT bindings problem. ;-)

-Doug

[PATCH 2/9] drm/panel: Check for already prepared/enabled in drm_panel

[Douglas Anderson]

In a whole pile of panel drivers, we have code to make the
prepare/unprepare/enable/disable callbacks behave as no-ops if they've
already been called. It's silly to have this code duplicated
everywhere. Add it to the core instead so that we can eventually
delete it from all the drivers. Note: to get some idea of the
duplicated code, try:
  git grep 'if.*>prepared' -- drivers/gpu/drm/panel
  git grep 'if.*>enabled' -- drivers/gpu/drm/panel

NOTE: arguably, the right thing to do here is actually to skip this
patch and simply remove all the extra checks from the individual
drivers. Perhaps the checks were needed at some point in time in the
past but maybe they no longer are? Certainly as we continue
transitioning over to "panel_bridge" then we expect there to be much
less variety in how these calls are made. When we're called as part of
the bridge chain, things should be pretty simple. In fact, there was
some discussion in the past about these checks [1], including a
discussion about whether the checks were needed and whether the calls
ought to be refcounted. At the time, I decided not to mess with it
because it felt too risky.

Looking closer at it now, I'm fairly certain that nothing in the
existing codebase is expecting these calls to be refcounted. The only
real question is whether someone is already doing something to ensure
prepare()/unprepare() match and enabled()/disable() match. I would say
that, even if there is something else ensuring that things match,
there's enough complexity that adding an extra bool and an extra
double-check here is a good idea. Let's add a drm_warn() to let people
know that it's considered a minor error to take advantage of
drm_panel's double-checking but we'll still make things work fine.

[1] https://lore.kernel.org/r/20210416153909.v4.27.I502f2a92ddd36c3d28d014dd75e170c2d405a0a5@changeid

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/gpu/drm/drm_panel.c | 49 ++++++++++++++++++++++++++++++++-----
 include/drm/drm_panel.h     | 14 +++++++++++
 2 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index f634371c717a..4e1c4e42575b 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -105,11 +105,22 @@ EXPORT_SYMBOL(drm_panel_remove);
  */
 int drm_panel_prepare(struct drm_panel *panel)
 {
+	int ret;
+
 	if (!panel)
 		return -EINVAL;
 
-	if (panel->funcs && panel->funcs->prepare)
-		return panel->funcs->prepare(panel);
+	if (panel->prepared) {
+		dev_warn(panel->dev, "Skipping prepare of already prepared panel\n");
+		return 0;
+	}
+
+	if (panel->funcs && panel->funcs->prepare) {
+		ret = panel->funcs->prepare(panel);
+		if (ret < 0)
+			return ret;
+	}
+	panel->prepared = true;
 
 	return 0;
 }
@@ -128,11 +139,22 @@ EXPORT_SYMBOL(drm_panel_prepare);
  */
 int drm_panel_unprepare(struct drm_panel *panel)
 {
+	int ret;
+
 	if (!panel)
 		return -EINVAL;
 
-	if (panel->funcs && panel->funcs->unprepare)
-		return panel->funcs->unprepare(panel);
+	if (!panel->prepared) {
+		dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
+		return 0;
+	}
+
+	if (panel->funcs && panel->funcs->unprepare) {
+		ret = panel->funcs->unprepare(panel);
+		if (ret < 0)
+			return ret;
+	}
+	panel->prepared = false;
 
 	return 0;
 }
@@ -155,11 +177,17 @@ int drm_panel_enable(struct drm_panel *panel)
 	if (!panel)
 		return -EINVAL;
 
+	if (panel->enabled) {
+		dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
+		return 0;
+	}
+
 	if (panel->funcs && panel->funcs->enable) {
 		ret = panel->funcs->enable(panel);
 		if (ret < 0)
 			return ret;
 	}
+	panel->enabled = true;
 
 	ret = backlight_enable(panel->backlight);
 	if (ret < 0)
@@ -187,13 +215,22 @@ int drm_panel_disable(struct drm_panel *panel)
 	if (!panel)
 		return -EINVAL;
 
+	if (!panel->enabled) {
+		dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
+		return 0;
+	}
+
 	ret = backlight_disable(panel->backlight);
 	if (ret < 0)
 		DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
 			     ret);
 
-	if (panel->funcs && panel->funcs->disable)
-		return panel->funcs->disable(panel);
+	if (panel->funcs && panel->funcs->disable) {
+		ret = panel->funcs->disable(panel);
+		if (ret < 0)
+			return ret;
+	}
+	panel->enabled = false;
 
 	return 0;
 }
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 432fab2347eb..c6cf75909389 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -198,6 +198,20 @@ struct drm_panel {
 	 * the panel is powered up.
 	 */
 	bool prepare_prev_first;
+
+	/**
+	 * @prepared:
+	 *
+	 * If true then the panel has been prepared.
+	 */
+	bool prepared;
+
+	/**
+	 * @enabled:
+	 *
+	 * If true then the panel has been enabled.
+	 */
+	bool enabled;
 };
 
 void drm_panel_init(struct drm_panel *panel, struct device *dev,
-- 
2.40.1.698.g37aff9b760-goog

Re: [PATCH 2/9] drm/panel: Check for already prepared/enabled in drm_panel

[Neil Armstrong]

Hi,

On 23/05/2023 21:27, Douglas Anderson wrote:
> In a whole pile of panel drivers, we have code to make the
> prepare/unprepare/enable/disable callbacks behave as no-ops if they've
> already been called. It's silly to have this code duplicated
> everywhere. Add it to the core instead so that we can eventually
> delete it from all the drivers. Note: to get some idea of the
> duplicated code, try:
>    git grep 'if.*>prepared' -- drivers/gpu/drm/panel
>    git grep 'if.*>enabled' -- drivers/gpu/drm/panel
> 
> NOTE: arguably, the right thing to do here is actually to skip this
> patch and simply remove all the extra checks from the individual
> drivers. Perhaps the checks were needed at some point in time in the
> past but maybe they no longer are? Certainly as we continue
> transitioning over to "panel_bridge" then we expect there to be much
> less variety in how these calls are made. When we're called as part of
> the bridge chain, things should be pretty simple. In fact, there was
> some discussion in the past about these checks [1], including a
> discussion about whether the checks were needed and whether the calls
> ought to be refcounted. At the time, I decided not to mess with it
> because it felt too risky.
> 
> Looking closer at it now, I'm fairly certain that nothing in the
> existing codebase is expecting these calls to be refcounted. The only
> real question is whether someone is already doing something to ensure
> prepare()/unprepare() match and enabled()/disable() match. I would say
> that, even if there is something else ensuring that things match,
> there's enough complexity that adding an extra bool and an extra
> double-check here is a good idea. Let's add a drm_warn() to let people
> know that it's considered a minor error to take advantage of
> drm_panel's double-checking but we'll still make things work fine.
> 
> [1] https://lore.kernel.org/r/20210416153909.v4.27.I502f2a92ddd36c3d28d014dd75e170c2d405a0a5@changeid
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>   drivers/gpu/drm/drm_panel.c | 49 ++++++++++++++++++++++++++++++++-----
>   include/drm/drm_panel.h     | 14 +++++++++++
>   2 files changed, 57 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index f634371c717a..4e1c4e42575b 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -105,11 +105,22 @@ EXPORT_SYMBOL(drm_panel_remove);
>    */
>   int drm_panel_prepare(struct drm_panel *panel)
>   {
> +	int ret;
> +
>   	if (!panel)
>   		return -EINVAL;
>   
> -	if (panel->funcs && panel->funcs->prepare)
> -		return panel->funcs->prepare(panel);
> +	if (panel->prepared) {
> +		dev_warn(panel->dev, "Skipping prepare of already prepared panel\n");
> +		return 0;
> +	}
> +
> +	if (panel->funcs && panel->funcs->prepare) {
> +		ret = panel->funcs->prepare(panel);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	panel->prepared = true;
>   
>   	return 0;
>   }
> @@ -128,11 +139,22 @@ EXPORT_SYMBOL(drm_panel_prepare);
>    */
>   int drm_panel_unprepare(struct drm_panel *panel)
>   {
> +	int ret;
> +
>   	if (!panel)
>   		return -EINVAL;
>   
> -	if (panel->funcs && panel->funcs->unprepare)
> -		return panel->funcs->unprepare(panel);
> +	if (!panel->prepared) {
> +		dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
> +		return 0;
> +	}
> +
> +	if (panel->funcs && panel->funcs->unprepare) {
> +		ret = panel->funcs->unprepare(panel);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	panel->prepared = false;
>   
>   	return 0;
>   }
> @@ -155,11 +177,17 @@ int drm_panel_enable(struct drm_panel *panel)
>   	if (!panel)
>   		return -EINVAL;
>   
> +	if (panel->enabled) {
> +		dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
> +		return 0;
> +	}
> +
>   	if (panel->funcs && panel->funcs->enable) {
>   		ret = panel->funcs->enable(panel);
>   		if (ret < 0)
>   			return ret;
>   	}
> +	panel->enabled = true;
>   
>   	ret = backlight_enable(panel->backlight);
>   	if (ret < 0)
> @@ -187,13 +215,22 @@ int drm_panel_disable(struct drm_panel *panel)
>   	if (!panel)
>   		return -EINVAL;
>   
> +	if (!panel->enabled) {
> +		dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
> +		return 0;
> +	}
> +
>   	ret = backlight_disable(panel->backlight);
>   	if (ret < 0)
>   		DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
>   			     ret);
>   
> -	if (panel->funcs && panel->funcs->disable)
> -		return panel->funcs->disable(panel);
> +	if (panel->funcs && panel->funcs->disable) {
> +		ret = panel->funcs->disable(panel);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	panel->enabled = false;
>   
>   	return 0;
>   }
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 432fab2347eb..c6cf75909389 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -198,6 +198,20 @@ struct drm_panel {
>   	 * the panel is powered up.
>   	 */
>   	bool prepare_prev_first;
> +
> +	/**
> +	 * @prepared:
> +	 *
> +	 * If true then the panel has been prepared.
> +	 */
> +	bool prepared;
> +
> +	/**
> +	 * @enabled:
> +	 *
> +	 * If true then the panel has been enabled.
> +	 */
> +	bool enabled;
>   };
>   
>   void drm_panel_init(struct drm_panel *panel, struct device *dev,

LGTM and let's cleanup the panel drivers

Acked-by: Neil Armstrong <neil.armstrong@linaro.org>

Re: [PATCH 2/9] drm/panel: Check for already prepared/enabled in drm_panel

[Doug Anderson]

Hi,

On Wed, May 24, 2023 at 2:52 AM Neil Armstrong
<neil.armstrong@linaro.org> wrote:
>
> Hi,
>
> On 23/05/2023 21:27, Douglas Anderson wrote:
> > In a whole pile of panel drivers, we have code to make the
> > prepare/unprepare/enable/disable callbacks behave as no-ops if they've
> > already been called. It's silly to have this code duplicated
> > everywhere. Add it to the core instead so that we can eventually
> > delete it from all the drivers. Note: to get some idea of the
> > duplicated code, try:
> >    git grep 'if.*>prepared' -- drivers/gpu/drm/panel
> >    git grep 'if.*>enabled' -- drivers/gpu/drm/panel
> >
> > NOTE: arguably, the right thing to do here is actually to skip this
> > patch and simply remove all the extra checks from the individual
> > drivers. Perhaps the checks were needed at some point in time in the
> > past but maybe they no longer are? Certainly as we continue
> > transitioning over to "panel_bridge" then we expect there to be much
> > less variety in how these calls are made. When we're called as part of
> > the bridge chain, things should be pretty simple. In fact, there was
> > some discussion in the past about these checks [1], including a
> > discussion about whether the checks were needed and whether the calls
> > ought to be refcounted. At the time, I decided not to mess with it
> > because it felt too risky.
> >
> > Looking closer at it now, I'm fairly certain that nothing in the
> > existing codebase is expecting these calls to be refcounted. The only
> > real question is whether someone is already doing something to ensure
> > prepare()/unprepare() match and enabled()/disable() match. I would say
> > that, even if there is something else ensuring that things match,
> > there's enough complexity that adding an extra bool and an extra
> > double-check here is a good idea. Let's add a drm_warn() to let people
> > know that it's considered a minor error to take advantage of
> > drm_panel's double-checking but we'll still make things work fine.
> >
> > [1] https://lore.kernel.org/r/20210416153909.v4.27.I502f2a92ddd36c3d28d014dd75e170c2d405a0a5@changeid
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> >   drivers/gpu/drm/drm_panel.c | 49 ++++++++++++++++++++++++++++++++-----
> >   include/drm/drm_panel.h     | 14 +++++++++++
> >   2 files changed, 57 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> > index f634371c717a..4e1c4e42575b 100644
> > --- a/drivers/gpu/drm/drm_panel.c
> > +++ b/drivers/gpu/drm/drm_panel.c
> > @@ -105,11 +105,22 @@ EXPORT_SYMBOL(drm_panel_remove);
> >    */
> >   int drm_panel_prepare(struct drm_panel *panel)
> >   {
> > +     int ret;
> > +
> >       if (!panel)
> >               return -EINVAL;
> >
> > -     if (panel->funcs && panel->funcs->prepare)
> > -             return panel->funcs->prepare(panel);
> > +     if (panel->prepared) {
> > +             dev_warn(panel->dev, "Skipping prepare of already prepared panel\n");
> > +             return 0;
> > +     }
> > +
> > +     if (panel->funcs && panel->funcs->prepare) {
> > +             ret = panel->funcs->prepare(panel);
> > +             if (ret < 0)
> > +                     return ret;
> > +     }
> > +     panel->prepared = true;
> >
> >       return 0;
> >   }
> > @@ -128,11 +139,22 @@ EXPORT_SYMBOL(drm_panel_prepare);
> >    */
> >   int drm_panel_unprepare(struct drm_panel *panel)
> >   {
> > +     int ret;
> > +
> >       if (!panel)
> >               return -EINVAL;
> >
> > -     if (panel->funcs && panel->funcs->unprepare)
> > -             return panel->funcs->unprepare(panel);
> > +     if (!panel->prepared) {
> > +             dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
> > +             return 0;
> > +     }
> > +
> > +     if (panel->funcs && panel->funcs->unprepare) {
> > +             ret = panel->funcs->unprepare(panel);
> > +             if (ret < 0)
> > +                     return ret;
> > +     }
> > +     panel->prepared = false;
> >
> >       return 0;
> >   }
> > @@ -155,11 +177,17 @@ int drm_panel_enable(struct drm_panel *panel)
> >       if (!panel)
> >               return -EINVAL;
> >
> > +     if (panel->enabled) {
> > +             dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
> > +             return 0;
> > +     }
> > +
> >       if (panel->funcs && panel->funcs->enable) {
> >               ret = panel->funcs->enable(panel);
> >               if (ret < 0)
> >                       return ret;
> >       }
> > +     panel->enabled = true;
> >
> >       ret = backlight_enable(panel->backlight);
> >       if (ret < 0)
> > @@ -187,13 +215,22 @@ int drm_panel_disable(struct drm_panel *panel)
> >       if (!panel)
> >               return -EINVAL;
> >
> > +     if (!panel->enabled) {
> > +             dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
> > +             return 0;
> > +     }
> > +
> >       ret = backlight_disable(panel->backlight);
> >       if (ret < 0)
> >               DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
> >                            ret);
> >
> > -     if (panel->funcs && panel->funcs->disable)
> > -             return panel->funcs->disable(panel);
> > +     if (panel->funcs && panel->funcs->disable) {
> > +             ret = panel->funcs->disable(panel);
> > +             if (ret < 0)
> > +                     return ret;
> > +     }
> > +     panel->enabled = false;
> >
> >       return 0;
> >   }
> > diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> > index 432fab2347eb..c6cf75909389 100644
> > --- a/include/drm/drm_panel.h
> > +++ b/include/drm/drm_panel.h
> > @@ -198,6 +198,20 @@ struct drm_panel {
> >        * the panel is powered up.
> >        */
> >       bool prepare_prev_first;
> > +
> > +     /**
> > +      * @prepared:
> > +      *
> > +      * If true then the panel has been prepared.
> > +      */
> > +     bool prepared;
> > +
> > +     /**
> > +      * @enabled:
> > +      *
> > +      * If true then the panel has been enabled.
> > +      */
> > +     bool enabled;
> >   };
> >
> >   void drm_panel_init(struct drm_panel *panel, struct device *dev,
>
> LGTM and let's cleanup the panel drivers
>
> Acked-by: Neil Armstrong <neil.armstrong@linaro.org>

Thanks! For now I'll hold off on landing to see where this series ends
up. If the series ends up looking good we'll have to coordinate
landing the various bits between the drm and the hid trees and the
second drm patch in my series depends on this one>

If my series implodes I'll land this one on its own with your Ack. In
any case, once this lands somewhere I'll take an AI to cleanup the
panels.

-Doug

Re: [PATCH 2/9] drm/panel: Check for already prepared/enabled in drm_panel

[Chris Morgan]

On Tue, May 23, 2023 at 12:27:56PM -0700, Douglas Anderson wrote:
> In a whole pile of panel drivers, we have code to make the
> prepare/unprepare/enable/disable callbacks behave as no-ops if they've
> already been called. It's silly to have this code duplicated
> everywhere. Add it to the core instead so that we can eventually
> delete it from all the drivers. Note: to get some idea of the
> duplicated code, try:
>   git grep 'if.*>prepared' -- drivers/gpu/drm/panel
>   git grep 'if.*>enabled' -- drivers/gpu/drm/panel
> 
> NOTE: arguably, the right thing to do here is actually to skip this
> patch and simply remove all the extra checks from the individual
> drivers. Perhaps the checks were needed at some point in time in the
> past but maybe they no longer are? Certainly as we continue

For some reason I haven't dug into in greater detail on my RK3326 and
RK3568 boards I hit an issue on suspend/shutdown whereby the unprepare
is called multiple times. I suspect it's the dw-mipi-dsi-rockchip.c
driver and the dw-mipi-dsi.c drivers both calling the unprepare, but
I haven't been able to debug it completely yet.

> transitioning over to "panel_bridge" then we expect there to be much
> less variety in how these calls are made. When we're called as part of
> the bridge chain, things should be pretty simple. In fact, there was
> some discussion in the past about these checks [1], including a
> discussion about whether the checks were needed and whether the calls
> ought to be refcounted. At the time, I decided not to mess with it
> because it felt too risky.
> 
> Looking closer at it now, I'm fairly certain that nothing in the
> existing codebase is expecting these calls to be refcounted. The only

Regulator unbalanced disables are a bane of my existence. For the
panel-newvision-nv3051d.c driver I upstreamed a few releases ago I was
told to not include the is_enabled logic and as a result I get a
warning on suspend or shutdown when it disables the panel. Unprepare
gets called twice and that results in an unbalanced regulator disable.

> real question is whether someone is already doing something to ensure
> prepare()/unprepare() match and enabled()/disable() match. I would say
> that, even if there is something else ensuring that things match,
> there's enough complexity that adding an extra bool and an extra
> double-check here is a good idea. Let's add a drm_warn() to let people
> know that it's considered a minor error to take advantage of
> drm_panel's double-checking but we'll still make things work fine.
> 
> [1] https://lore.kernel.org/r/20210416153909.v4.27.I502f2a92ddd36c3d28d014dd75e170c2d405a0a5@changeid
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  drivers/gpu/drm/drm_panel.c | 49 ++++++++++++++++++++++++++++++++-----
>  include/drm/drm_panel.h     | 14 +++++++++++
>  2 files changed, 57 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index f634371c717a..4e1c4e42575b 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -105,11 +105,22 @@ EXPORT_SYMBOL(drm_panel_remove);
>   */
>  int drm_panel_prepare(struct drm_panel *panel)
>  {
> +	int ret;
> +
>  	if (!panel)
>  		return -EINVAL;
>  
> -	if (panel->funcs && panel->funcs->prepare)
> -		return panel->funcs->prepare(panel);
> +	if (panel->prepared) {
> +		dev_warn(panel->dev, "Skipping prepare of already prepared panel\n");
> +		return 0;
> +	}
> +
> +	if (panel->funcs && panel->funcs->prepare) {
> +		ret = panel->funcs->prepare(panel);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	panel->prepared = true;
>  
>  	return 0;
>  }
> @@ -128,11 +139,22 @@ EXPORT_SYMBOL(drm_panel_prepare);
>   */
>  int drm_panel_unprepare(struct drm_panel *panel)
>  {
> +	int ret;
> +
>  	if (!panel)
>  		return -EINVAL;
>  
> -	if (panel->funcs && panel->funcs->unprepare)
> -		return panel->funcs->unprepare(panel);
> +	if (!panel->prepared) {
> +		dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
> +		return 0;
> +	}
> +
> +	if (panel->funcs && panel->funcs->unprepare) {
> +		ret = panel->funcs->unprepare(panel);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	panel->prepared = false;
>  
>  	return 0;
>  }
> @@ -155,11 +177,17 @@ int drm_panel_enable(struct drm_panel *panel)
>  	if (!panel)
>  		return -EINVAL;
>  
> +	if (panel->enabled) {
> +		dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
> +		return 0;
> +	}
> +
>  	if (panel->funcs && panel->funcs->enable) {
>  		ret = panel->funcs->enable(panel);
>  		if (ret < 0)
>  			return ret;
>  	}
> +	panel->enabled = true;
>  
>  	ret = backlight_enable(panel->backlight);
>  	if (ret < 0)
> @@ -187,13 +215,22 @@ int drm_panel_disable(struct drm_panel *panel)
>  	if (!panel)
>  		return -EINVAL;
>  
> +	if (!panel->enabled) {
> +		dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
> +		return 0;
> +	}
> +
>  	ret = backlight_disable(panel->backlight);
>  	if (ret < 0)
>  		DRM_DEV_INFO(panel->dev, "failed to disable backlight: %d\n",
>  			     ret);
>  
> -	if (panel->funcs && panel->funcs->disable)
> -		return panel->funcs->disable(panel);
> +	if (panel->funcs && panel->funcs->disable) {
> +		ret = panel->funcs->disable(panel);
> +		if (ret < 0)
> +			return ret;
> +	}
> +	panel->enabled = false;
>  
>  	return 0;
>  }
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 432fab2347eb..c6cf75909389 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -198,6 +198,20 @@ struct drm_panel {
>  	 * the panel is powered up.
>  	 */
>  	bool prepare_prev_first;
> +
> +	/**
> +	 * @prepared:
> +	 *
> +	 * If true then the panel has been prepared.
> +	 */
> +	bool prepared;
> +
> +	/**
> +	 * @enabled:
> +	 *
> +	 * If true then the panel has been enabled.
> +	 */
> +	bool enabled;
>  };
>  
>  void drm_panel_init(struct drm_panel *panel, struct device *dev,
> -- 
> 2.40.1.698.g37aff9b760-goog
> 

Thank you for looking into this more. It's one of the last QOL bugs
for some devices I'm working on, even if the end result is no big
deal (the other QOL bug involves a WARN on probing a rotated panel).

Re: [PATCH 2/9] drm/panel: Check for already prepared/enabled in drm_panel

[Doug Anderson]

Hi,

On Wed, May 24, 2023 at 9:19 AM Chris Morgan <macroalpha82@gmail.com> wrote:
>
> Thank you for looking into this more. It's one of the last QOL bugs
> for some devices I'm working on, even if the end result is no big
> deal (the other QOL bug involves a WARN on probing a rotated panel).

Glad it'll be helpful!

For the WARN on probing a rotated panel I thought there was some
progress on that front. Commit e3ea1806e4ad ("drm/bridge: panel: Set
orientation on panel_bridge connector") or commit 15b9ca1641f0 ("drm:
Config orientation property if panel provides it") didn't help you?

[PATCH 3/9] drm/panel: Add a way for other devices to follow panel state

[Douglas Anderson]

These days, it's fairly common to see panels that have touchscreens
attached to them. The panel and the touchscreen can somewhat be
thought of as totally separate devices and, historically, this is how
Linux has treated them. However, treating them as separate isn't
necessarily the best way to model the two devices, it was just that
there was no better way. Specifically, there is little practical
reason to have the touchscreen powered on when the panel is turned
off, but if we model the devices separately we have no way to keep the
two devices' power states in sync with each other.

The issue described above makes it sound as if the problem here is
just about efficiency. We're wasting power keeping the touchscreen
powered up when the screen is off. While that's true, the problem can
go deeper. Specifically, hardware designers see that there's no reason
to have the touchscreen on while the screen is off and then build
hardware assuming that software would never turn the touchscreen on
while the screen is off.

In the very simplest case of hardware designs like this, the
touchscreen and the panel share some power rails. In most cases, this
turns out not to be terrible and is, again, just a little less
efficient. Specifically if we tell Linux that the touchscreen and the
panel are using the same rails then Linux will keep the rails on when
_either_ device is turned on. That ends to work OK-ish, but now if you
turn the panel off not only will the touchscreen remain powered, but
the power rails for the panel itself won't be switched off, burning
extra power.

The above two inefficiencies are _extra_ minor when you consider the
fact that laptops rarely spend much time with the screen off. The main
use case would be when an external screen (and presumably a power
supply) is attached.

Unfortunately, it gets worse from here. On sc7180-trogdor-homestar,
for instance, the display's TCON (timing controller) sometimes crashes
if you didn't power cycle it whenever you stopp and restart the video
stream (like during a modeset). The touchscreen keeping the power
rails on caused real problems. One proposal in the homestar timeframe
was to move the touchscreen to an always-on rail, dedicating the main
power rail to the panel. That caused _different_ problems as talked
about in commit 557e05fa9fdd ("HID: i2c-hid: goodix: Stop tying the
reset line to the regulator"). The end result of all of this was to
add an extra regulator to the board, increasing cost.

Recently, Cong Yang posted a patch [1] where things are even worse.
The panel and touch controller on that system seem even more
intimately tied together and really can't be thought of separately.

To address this issue, let's start allowing devices to register
themselves as "panel followers". These devices will get called after a
panel has been powered on and before a panel is powered off. This
makes the panel the primary device in charge of the power state, which
matches how userspace uses it.

The panel follower API should be fairly straightforward to use. The
current code assumes that panel followers are using device tree and
have a "panel" property pointing to the panel to follow. More
flexibility and non-DT implementations could be added as needed.

Right now, panel followers can follow the prepare/unprepare functions.
There could be arguments made that, instead, they should follow
enable/disable. I've chosen prepare/unprepare for now since those
functions are guaranteed to power up/power down the panel and it seems
better to start the process earlier.

[1] 20230519032316.3464732-1-yangcong5@huaqin.corp-partner.google.com

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/gpu/drm/drm_panel.c | 149 +++++++++++++++++++++++++++++++++++-
 include/drm/drm_panel.h     |  75 ++++++++++++++++++
 2 files changed, 220 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index 4e1c4e42575b..c4d9db435f15 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -58,6 +58,8 @@ void drm_panel_init(struct drm_panel *panel, struct device *dev,
 		    const struct drm_panel_funcs *funcs, int connector_type)
 {
 	INIT_LIST_HEAD(&panel->list);
+	INIT_LIST_HEAD(&panel->followers);
+	mutex_init(&panel->follower_lock);
 	panel->dev = dev;
 	panel->funcs = funcs;
 	panel->connector_type = connector_type;
@@ -105,6 +107,7 @@ EXPORT_SYMBOL(drm_panel_remove);
  */
 int drm_panel_prepare(struct drm_panel *panel)
 {
+	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
@@ -115,14 +118,27 @@ int drm_panel_prepare(struct drm_panel *panel)
 		return 0;
 	}
 
+	mutex_lock(&panel->follower_lock);
+
 	if (panel->funcs && panel->funcs->prepare) {
 		ret = panel->funcs->prepare(panel);
 		if (ret < 0)
-			return ret;
+			goto exit;
 	}
 	panel->prepared = true;
 
-	return 0;
+	list_for_each_entry(follower, &panel->followers, list) {
+		ret = follower->funcs->panel_prepared(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_prepared, ret);
+	}
+
+	ret = 0;
+exit:
+	mutex_unlock(&panel->follower_lock);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_panel_prepare);
 
@@ -139,6 +155,7 @@ EXPORT_SYMBOL(drm_panel_prepare);
  */
 int drm_panel_unprepare(struct drm_panel *panel)
 {
+	struct drm_panel_follower *follower;
 	int ret;
 
 	if (!panel)
@@ -149,14 +166,27 @@ int drm_panel_unprepare(struct drm_panel *panel)
 		return 0;
 	}
 
+	mutex_lock(&panel->follower_lock);
+
+	list_for_each_entry(follower, &panel->followers, list) {
+		ret = follower->funcs->panel_unpreparing(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_unpreparing, ret);
+	}
+
 	if (panel->funcs && panel->funcs->unprepare) {
 		ret = panel->funcs->unprepare(panel);
 		if (ret < 0)
-			return ret;
+			goto exit;
 	}
 	panel->prepared = false;
 
-	return 0;
+	ret = 0;
+exit:
+	mutex_unlock(&panel->follower_lock);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_panel_unprepare);
 
@@ -342,6 +372,117 @@ int of_drm_get_panel_orientation(const struct device_node *np,
 EXPORT_SYMBOL(of_drm_get_panel_orientation);
 #endif
 
+/**
+ * drm_panel_add_follower() - Register something to follow panel enable state.
+ * @follower_dev: The 'struct device' for the follower.
+ * @follower:     The panel follower descriptor for the follower.
+ *
+ * A panel follower is called right after preparing the panel and right before
+ * unpreparing the panel. It's primary intention is to power on an associated
+ * touchscreen, though it could be used for any similar devices. Multiple
+ * devices are allowed the follow the same panel.
+ *
+ * If a follower is added to a panel that's already been turned on, the
+ * follower's prepare callback is called right away.
+ *
+ * At the moment panels can only be followed on device tree enabled systems.
+ * The "panel" property of the follower points to the panel to be followed.
+ *
+ * Return: 0 or an error code.
+ */
+int drm_panel_add_follower(struct device *follower_dev,
+			   struct drm_panel_follower *follower)
+{
+	struct device_node *panel_np;
+	struct drm_panel *panel;
+	int ret;
+
+	panel_np = of_parse_phandle(follower_dev->of_node, "panel", 0);
+	if (!panel_np)
+		return -ENODEV;
+
+	panel = of_drm_find_panel(panel_np);
+	of_node_put(panel_np);
+	if (IS_ERR(panel))
+		return PTR_ERR(panel);
+
+	get_device(panel->dev);
+	follower->panel = panel;
+
+	mutex_lock(&panel->follower_lock);
+
+	list_add_tail(&follower->list, &panel->followers);
+	if (panel->prepared) {
+		ret = follower->funcs->panel_prepared(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_prepared, ret);
+	}
+
+	mutex_unlock(&panel->follower_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_panel_add_follower);
+
+/**
+ * drm_panel_remove_follower() - Reverse drm_panel_add_follower().
+ * @follower:     The panel follower descriptor for the follower.
+ *
+ * Undo drm_panel_add_follower(). This includes calling the follower's disable
+ * function if we're removed from a panel that's currently enabled.
+ *
+ * Return: 0 or an error code.
+ */
+void drm_panel_remove_follower(struct drm_panel_follower *follower)
+{
+	struct drm_panel *panel = follower->panel;
+	int ret;
+
+	mutex_lock(&panel->follower_lock);
+
+	if (panel->prepared) {
+		ret = follower->funcs->panel_unpreparing(follower);
+		if (ret < 0)
+			dev_info(panel->dev, "%ps failed: %d\n",
+				 follower->funcs->panel_unpreparing, ret);
+	}
+	list_del_init(&follower->list);
+
+	mutex_unlock(&panel->follower_lock);
+
+	put_device(panel->dev);
+}
+EXPORT_SYMBOL(drm_panel_remove_follower);
+
+static void drm_panel_remove_follower_void(void *follower)
+{
+	drm_panel_remove_follower(follower);
+}
+
+/**
+ * devm_drm_panel_add_follower() - devm version of drm_panel_add_follower()
+ * @follower_dev: The 'struct device' for the follower.
+ * @follower:     The panel follower descriptor for the follower.
+ *
+ * Handles calling drm_panel_remove_follower() using devm on the follower_dev.
+ *
+ * Return: 0 or an error code.
+ */
+int devm_drm_panel_add_follower(struct device *follower_dev,
+				struct drm_panel_follower *follower)
+{
+	int ret;
+
+	ret = drm_panel_add_follower(follower_dev, follower);
+	if (ret)
+		return ret;
+
+	return devm_add_action_or_reset(follower_dev,
+					drm_panel_remove_follower_void, follower);
+}
+EXPORT_SYMBOL(devm_drm_panel_add_follower);
+
 #if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
 /**
  * drm_panel_of_backlight - use backlight device node for backlight
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index c6cf75909389..e0a4d2f6f7fb 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -27,12 +27,14 @@
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/list.h>
+#include <linux/mutex.h>
 
 struct backlight_device;
 struct dentry;
 struct device_node;
 struct drm_connector;
 struct drm_device;
+struct drm_panel_follower;
 struct drm_panel;
 struct display_timing;
 
@@ -144,6 +146,45 @@ struct drm_panel_funcs {
 	void (*debugfs_init)(struct drm_panel *panel, struct dentry *root);
 };
 
+struct drm_panel_follower_funcs {
+	/**
+	 * @panel_prepared:
+	 *
+	 * Called after the panel has been powered on.
+	 */
+	int (*panel_prepared)(struct drm_panel_follower *follower);
+
+	/**
+	 * @panel_unpreparing:
+	 *
+	 * Called before the panel is powered off.
+	 */
+	int (*panel_unpreparing)(struct drm_panel_follower *follower);
+};
+
+struct drm_panel_follower {
+	/**
+	 * @funcs:
+	 *
+	 * Dependent device callbacks; should be initted by the caller.
+	 */
+	const struct drm_panel_follower_funcs *funcs;
+
+	/**
+	 * @list
+	 *
+	 * Used for linking into panel's list; set by drm_panel_add_follower().
+	 */
+	struct list_head list;
+
+	/**
+	 * @panel
+	 *
+	 * The panel we're dependent on; set by drm_panel_add_follower().
+	 */
+	struct drm_panel *panel;
+};
+
 /**
  * struct drm_panel - DRM panel object
  */
@@ -189,6 +230,20 @@ struct drm_panel {
 	 */
 	struct list_head list;
 
+	/**
+	 * @followers:
+	 *
+	 * A list of struct drm_panel_follower dependent on this panel.
+	 */
+	struct list_head followers;
+
+	/**
+	 * @followers_lock:
+	 *
+	 * Lock for followers list.
+	 */
+	struct mutex follower_lock;
+
 	/**
 	 * @prepare_prev_first:
 	 *
@@ -246,6 +301,26 @@ static inline int of_drm_get_panel_orientation(const struct device_node *np,
 }
 #endif
 
+#if defined(CONFIG_DRM_PANEL)
+int drm_panel_add_follower(struct device *follower_dev,
+			   struct drm_panel_follower *follower);
+void drm_panel_remove_follower(struct drm_panel_follower *follower);
+int devm_drm_panel_add_follower(struct device *follower_dev,
+				struct drm_panel_follower *follower);
+#else
+static inline int drm_panel_add_follower(struct device *follower_dev,
+					 struct drm_panel_follower *follower)
+{
+	return -ENODEV;
+}
+static inline void drm_panel_remove_follower(struct drm_panel_follower *follower) { }
+static inline int devm_drm_panel_add_follower(struct device *follower_dev,
+					      struct drm_panel_follower *follower)
+{
+	return -ENODEV;
+}
+#endif
+
 #if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
 	(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
 int drm_panel_of_backlight(struct drm_panel *panel);
-- 
2.40.1.698.g37aff9b760-goog

[PATCH 4/9] HID: i2c-hid: Switch to SYSTEM_SLEEP_PM_OPS()

[Douglas Anderson]

The SYSTEM_SLEEP_PM_OPS() allows us to get rid of '#ifdef
CONFIG_PM_SLEEP', as talked about in commit 1a3c7bb08826 ("PM: core:
Add new *_PM_OPS macros, deprecate old ones").

This change is expected to have no functional effect.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/hid/i2c-hid/i2c-hid-core.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index efbba0465eef..19d985c20a5c 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -1085,7 +1085,6 @@ void i2c_hid_core_shutdown(struct i2c_client *client)
 }
 EXPORT_SYMBOL_GPL(i2c_hid_core_shutdown);
 
-#ifdef CONFIG_PM_SLEEP
 static int i2c_hid_core_suspend(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
@@ -1138,10 +1137,9 @@ static int i2c_hid_core_resume(struct device *dev)
 
 	return hid_driver_reset_resume(hid);
 }
-#endif
 
 const struct dev_pm_ops i2c_hid_core_pm = {
-	SET_SYSTEM_SLEEP_PM_OPS(i2c_hid_core_suspend, i2c_hid_core_resume)
+	SYSTEM_SLEEP_PM_OPS(i2c_hid_core_suspend, i2c_hid_core_resume)
 };
 EXPORT_SYMBOL_GPL(i2c_hid_core_pm);
 
-- 
2.40.1.698.g37aff9b760-goog

[PATCH 5/9] HID: i2c-hid: Rearrange probe() to power things up later

[Douglas Anderson]

In a future patch, we want to change i2c-hid not to necessarily power
up the touchscreen during probe. In preparation for that, rearrange
the probe function so that we put as much stuff _before_ powering up
the device as possible.

This change is expected to have no functional effect.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/hid/i2c-hid/i2c-hid-core.c | 124 ++++++++++++++++++-----------
 1 file changed, 77 insertions(+), 47 deletions(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 19d985c20a5c..fb5ebf3ca739 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -855,7 +855,8 @@ static int i2c_hid_init_irq(struct i2c_client *client)
 		irqflags = IRQF_TRIGGER_LOW;
 
 	ret = request_threaded_irq(client->irq, NULL, i2c_hid_irq,
-				   irqflags | IRQF_ONESHOT, client->name, ihid);
+				   irqflags | IRQF_ONESHOT | IRQF_NO_AUTOEN,
+				   client->name, ihid);
 	if (ret < 0) {
 		dev_warn(&client->dev,
 			"Could not register for %s interrupt, irq = %d,"
@@ -940,6 +941,72 @@ static void i2c_hid_core_shutdown_tail(struct i2c_hid *ihid)
 	ihid->ops->shutdown_tail(ihid->ops);
 }
 
+/**
+ * i2c_hid_core_initial_power_up() - First time power up of the i2c-hid device.
+ * @ihid: The ihid object created during probe.
+ *
+ * This function is called at probe time.
+ *
+ * The initial power on is where we do some basic validation that the device
+ * exists, where we fetch the HID descriptor, and where we create the actual
+ * HID devices.
+ *
+ * Return: 0 or error code.
+ */
+int i2c_hid_core_initial_power_up(struct i2c_hid *ihid)
+{
+	struct i2c_client *client = ihid->client;
+	struct hid_device *hid = ihid->hid;
+	int ret;
+
+	ret = i2c_hid_core_power_up(ihid);
+	if (ret)
+		return ret;
+
+	/* Make sure there is something at this address */
+	ret = i2c_smbus_read_byte(client);
+	if (ret < 0) {
+		i2c_hid_dbg(ihid, "nothing at this address: %d\n", ret);
+		ret = -ENXIO;
+		goto err;
+	}
+
+	ret = i2c_hid_fetch_hid_descriptor(ihid);
+	if (ret < 0) {
+		dev_err(&client->dev,
+			"Failed to fetch the HID Descriptor\n");
+		goto err;
+	}
+
+	enable_irq(client->irq);
+
+	hid->version = le16_to_cpu(ihid->hdesc.bcdVersion);
+	hid->vendor = le16_to_cpu(ihid->hdesc.wVendorID);
+	hid->product = le16_to_cpu(ihid->hdesc.wProductID);
+
+	hid->initial_quirks |= i2c_hid_get_dmi_quirks(hid->vendor,
+						      hid->product);
+
+	snprintf(hid->name, sizeof(hid->name), "%s %04X:%04X",
+		 client->name, (u16)hid->vendor, (u16)hid->product);
+	strscpy(hid->phys, dev_name(&client->dev), sizeof(hid->phys));
+
+	ihid->quirks = i2c_hid_lookup_quirk(hid->vendor, hid->product);
+
+	ret = hid_add_device(hid);
+	if (ret) {
+		if (ret != -ENODEV)
+			hid_err(client, "can't add hid device: %d\n", ret);
+		goto err;
+	}
+
+	return 0;
+
+err:
+	i2c_hid_core_power_down(ihid);
+	return ret;
+}
+
 int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 		       u16 hid_descriptor_address, u32 quirks)
 {
@@ -966,16 +1033,10 @@ int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 	if (!ihid)
 		return -ENOMEM;
 
-	ihid->ops = ops;
-
-	ret = i2c_hid_core_power_up(ihid);
-	if (ret)
-		return ret;
-
 	i2c_set_clientdata(client, ihid);
 
+	ihid->ops = ops;
 	ihid->client = client;
-
 	ihid->wHIDDescRegister = cpu_to_le16(hid_descriptor_address);
 
 	init_waitqueue_head(&ihid->wait);
@@ -986,28 +1047,12 @@ int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 	 * real computation later. */
 	ret = i2c_hid_alloc_buffers(ihid, HID_MIN_BUFFER_SIZE);
 	if (ret < 0)
-		goto err_powered;
-
+		return ret;
 	device_enable_async_suspend(&client->dev);
 
-	/* Make sure there is something at this address */
-	ret = i2c_smbus_read_byte(client);
-	if (ret < 0) {
-		i2c_hid_dbg(ihid, "nothing at this address: %d\n", ret);
-		ret = -ENXIO;
-		goto err_powered;
-	}
-
-	ret = i2c_hid_fetch_hid_descriptor(ihid);
-	if (ret < 0) {
-		dev_err(&client->dev,
-			"Failed to fetch the HID Descriptor\n");
-		goto err_powered;
-	}
-
 	ret = i2c_hid_init_irq(client);
 	if (ret < 0)
-		goto err_powered;
+		goto err_buffers_allocated;
 
 	hid = hid_allocate_device();
 	if (IS_ERR(hid)) {
@@ -1021,26 +1066,11 @@ int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 	hid->ll_driver = &i2c_hid_ll_driver;
 	hid->dev.parent = &client->dev;
 	hid->bus = BUS_I2C;
-	hid->version = le16_to_cpu(ihid->hdesc.bcdVersion);
-	hid->vendor = le16_to_cpu(ihid->hdesc.wVendorID);
-	hid->product = le16_to_cpu(ihid->hdesc.wProductID);
-
 	hid->initial_quirks = quirks;
-	hid->initial_quirks |= i2c_hid_get_dmi_quirks(hid->vendor,
-						      hid->product);
-
-	snprintf(hid->name, sizeof(hid->name), "%s %04X:%04X",
-		 client->name, (u16)hid->vendor, (u16)hid->product);
-	strscpy(hid->phys, dev_name(&client->dev), sizeof(hid->phys));
-
-	ihid->quirks = i2c_hid_lookup_quirk(hid->vendor, hid->product);
 
-	ret = hid_add_device(hid);
-	if (ret) {
-		if (ret != -ENODEV)
-			hid_err(client, "can't add hid device: %d\n", ret);
+	ret = i2c_hid_core_initial_power_up(ihid);
+	if (ret)
 		goto err_mem_free;
-	}
 
 	return 0;
 
@@ -1050,9 +1080,9 @@ int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 err_irq:
 	free_irq(client->irq, ihid);
 
-err_powered:
-	i2c_hid_core_power_down(ihid);
+err_buffers_allocated:
 	i2c_hid_free_buffers(ihid);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(i2c_hid_core_probe);
@@ -1062,6 +1092,8 @@ void i2c_hid_core_remove(struct i2c_client *client)
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
 	struct hid_device *hid;
 
+	i2c_hid_core_power_down(ihid);
+
 	hid = ihid->hid;
 	hid_destroy_device(hid);
 
@@ -1069,8 +1101,6 @@ void i2c_hid_core_remove(struct i2c_client *client)
 
 	if (ihid->bufsize)
 		i2c_hid_free_buffers(ihid);
-
-	i2c_hid_core_power_down(ihid);
 }
 EXPORT_SYMBOL_GPL(i2c_hid_core_remove);
 
-- 
2.40.1.698.g37aff9b760-goog

[PATCH 6/9] HID: i2c-hid: Make suspend and resume into helper functions

[Douglas Anderson]

In a future patch we'd like to be able to call the current i2c-hid
suspend and resume functions from times other than system
suspend. Move the functions higher up in the file and have them take a
"struct i2c_hid" to make this simpler. We'll then add tiny wrappers of
the functions for use with system suspend.

This change is expected to have no functional effect.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/hid/i2c-hid/i2c-hid-core.c | 98 +++++++++++++++++-------------
 1 file changed, 56 insertions(+), 42 deletions(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index fb5ebf3ca739..34c0d98b4976 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -941,6 +941,57 @@ static void i2c_hid_core_shutdown_tail(struct i2c_hid *ihid)
 	ihid->ops->shutdown_tail(ihid->ops);
 }
 
+static int i2c_hid_core_suspend(struct i2c_hid *ihid)
+{
+	struct i2c_client *client = ihid->client;
+	struct hid_device *hid = ihid->hid;
+	int ret;
+
+	ret = hid_driver_suspend(hid, PMSG_SUSPEND);
+	if (ret < 0)
+		return ret;
+
+	/* Save some power */
+	i2c_hid_set_power(ihid, I2C_HID_PWR_SLEEP);
+
+	disable_irq(client->irq);
+
+	if (!device_may_wakeup(&client->dev))
+		i2c_hid_core_power_down(ihid);
+
+	return 0;
+}
+
+static int i2c_hid_core_resume(struct i2c_hid *ihid)
+{
+	struct i2c_client *client = ihid->client;
+	struct hid_device *hid = ihid->hid;
+	int ret;
+
+	if (!device_may_wakeup(&client->dev))
+		i2c_hid_core_power_up(ihid);
+
+	enable_irq(client->irq);
+
+	/* Instead of resetting device, simply powers the device on. This
+	 * solves "incomplete reports" on Raydium devices 2386:3118 and
+	 * 2386:4B33 and fixes various SIS touchscreens no longer sending
+	 * data after a suspend/resume.
+	 *
+	 * However some ALPS touchpads generate IRQ storm without reset, so
+	 * let's still reset them here.
+	 */
+	if (ihid->quirks & I2C_HID_QUIRK_RESET_ON_RESUME)
+		ret = i2c_hid_hwreset(ihid);
+	else
+		ret = i2c_hid_set_power(ihid, I2C_HID_PWR_ON);
+
+	if (ret)
+		return ret;
+
+	return hid_driver_reset_resume(hid);
+}
+
 /**
  * i2c_hid_core_initial_power_up() - First time power up of the i2c-hid device.
  * @ihid: The ihid object created during probe.
@@ -1115,61 +1166,24 @@ void i2c_hid_core_shutdown(struct i2c_client *client)
 }
 EXPORT_SYMBOL_GPL(i2c_hid_core_shutdown);
 
-static int i2c_hid_core_suspend(struct device *dev)
+static int i2c_hid_core_pm_suspend(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
-	struct hid_device *hid = ihid->hid;
-	int ret;
-
-	ret = hid_driver_suspend(hid, PMSG_SUSPEND);
-	if (ret < 0)
-		return ret;
 
-	/* Save some power */
-	i2c_hid_set_power(ihid, I2C_HID_PWR_SLEEP);
-
-	disable_irq(client->irq);
-
-	if (!device_may_wakeup(&client->dev))
-		i2c_hid_core_power_down(ihid);
-
-	return 0;
+	return i2c_hid_core_suspend(ihid);
 }
 
-static int i2c_hid_core_resume(struct device *dev)
+static int i2c_hid_core_pm_resume(struct device *dev)
 {
-	int ret;
 	struct i2c_client *client = to_i2c_client(dev);
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
-	struct hid_device *hid = ihid->hid;
 
-	if (!device_may_wakeup(&client->dev))
-		i2c_hid_core_power_up(ihid);
-
-	enable_irq(client->irq);
-
-	/* Instead of resetting device, simply powers the device on. This
-	 * solves "incomplete reports" on Raydium devices 2386:3118 and
-	 * 2386:4B33 and fixes various SIS touchscreens no longer sending
-	 * data after a suspend/resume.
-	 *
-	 * However some ALPS touchpads generate IRQ storm without reset, so
-	 * let's still reset them here.
-	 */
-	if (ihid->quirks & I2C_HID_QUIRK_RESET_ON_RESUME)
-		ret = i2c_hid_hwreset(ihid);
-	else
-		ret = i2c_hid_set_power(ihid, I2C_HID_PWR_ON);
-
-	if (ret)
-		return ret;
-
-	return hid_driver_reset_resume(hid);
+	return i2c_hid_core_resume(ihid);
 }
 
 const struct dev_pm_ops i2c_hid_core_pm = {
-	SYSTEM_SLEEP_PM_OPS(i2c_hid_core_suspend, i2c_hid_core_resume)
+	SYSTEM_SLEEP_PM_OPS(i2c_hid_core_pm_suspend, i2c_hid_core_pm_resume)
 };
 EXPORT_SYMBOL_GPL(i2c_hid_core_pm);
 
-- 
2.40.1.698.g37aff9b760-goog

[PATCH 7/9] HID: i2c-hid: Support being a panel follower

[Douglas Anderson]

As talked about in the patch ("drm/panel: Add a way for other devices
to follow panel state"), we really want to keep the power states of a
touchscreen and the panel it's attached to in sync with each other. In
that spirit, add support to i2c-hid to be a panel follower. This will
let the i2c-hid driver get informed when the panel is powered on and
off. From there we can match the i2c-hid device's power state to that
of the panel.

NOTE: this patch specifically _doesn't_ use pm_runtime to keep track
of / manage the power state of the i2c-hid device, even though my
first instinct said that would be the way to go. Specific problems
with using pm_runtime():
* The initial power up couldn't happen in a runtime resume function
  since it create sub-devices and, apparently, that's not good to do
  in your resume function.
* Managing our power state with pm_runtime meant fighting to make the
  right thing happen at system suspend to prevent the system from
  trying to resume us only to suspend us again. While this might be
  able to be solved, it added complexity.
Overall the code without pm_runtime() ended up being smaller and
easier to understand.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/hid/i2c-hid/i2c-hid-core.c | 82 +++++++++++++++++++++++++++++-
 1 file changed, 81 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 34c0d98b4976..f1bb89377e8d 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -38,6 +38,8 @@
 #include <linux/mutex.h>
 #include <asm/unaligned.h>
 
+#include <drm/drm_panel.h>
+
 #include "../hid-ids.h"
 #include "i2c-hid.h"
 
@@ -107,6 +109,8 @@ struct i2c_hid {
 	struct mutex		reset_lock;
 
 	struct i2chid_ops	*ops;
+	struct drm_panel_follower panel_follower;
+	bool			is_panel_follower;
 };
 
 static const struct i2c_hid_quirks {
@@ -1058,6 +1062,34 @@ int i2c_hid_core_initial_power_up(struct i2c_hid *ihid)
 	return ret;
 }
 
+int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)
+{
+	struct i2c_hid *ihid = container_of(follower, struct i2c_hid, panel_follower);
+	struct hid_device *hid = ihid->hid;
+
+	/*
+	 * hid->version is set on the first power up. If it's still zero then
+	 * this is the first power on so we should perform initial power up
+	 * steps.
+	 */
+	if (!hid->version)
+		return i2c_hid_core_initial_power_up(ihid);
+
+	return i2c_hid_core_resume(ihid);
+}
+
+int i2c_hid_core_panel_unpreparing(struct drm_panel_follower *follower)
+{
+	struct i2c_hid *ihid = container_of(follower, struct i2c_hid, panel_follower);
+
+	return i2c_hid_core_suspend(ihid);
+}
+
+static const struct drm_panel_follower_funcs i2c_hid_core_panel_follower_funcs = {
+	.panel_prepared = i2c_hid_core_panel_prepared,
+	.panel_unpreparing = i2c_hid_core_panel_unpreparing,
+};
+
 int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 		       u16 hid_descriptor_address, u32 quirks)
 {
@@ -1119,6 +1151,41 @@ int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 	hid->bus = BUS_I2C;
 	hid->initial_quirks = quirks;
 
+	/*
+	 * See if we're following a panel. If drm_panel_add_follower()
+	 * returns no error then we are.
+	 */
+	ihid->panel_follower.funcs = &i2c_hid_core_panel_follower_funcs;
+	ret = drm_panel_add_follower(&client->dev, &ihid->panel_follower);
+	if (!ret) {
+		/* We're a follower. That means we'll power things up later. */
+		ihid->is_panel_follower = true;
+
+		/*
+		 * If we're not in control of our own power up/power down then
+		 * we can't do the logic to manage wakeups. Give a warning if
+		 * a user thought that was possible then force the capability
+		 * off.
+		 */
+		if (device_can_wakeup(&client->dev)) {
+			dev_warn(&client->dev, "Can't wakeup if following panel\n");
+			device_set_wakeup_capable(&client->dev, false);
+		}
+
+		return 0;
+	}
+
+	/*
+	 * -ENODEV means that we're not following a panel, so any other error
+	 * is a real problem (like -EPROBE_DEFER, -ENOMEM, ...).
+	 */
+	if (ret != -ENODEV)
+		goto err_mem_free;
+
+	/*
+	 * We're not following a panel. That's fine and means that we
+	 * can power up right away.
+	 */
 	ret = i2c_hid_core_initial_power_up(ihid);
 	if (ret)
 		goto err_mem_free;
@@ -1143,7 +1210,14 @@ void i2c_hid_core_remove(struct i2c_client *client)
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
 	struct hid_device *hid;
 
-	i2c_hid_core_power_down(ihid);
+	/*
+	 * If we're a follower, the act of unfollowing will cause us to be
+	 * powered down. Otherwise we need to manually do it.
+	 */
+	if (ihid->is_panel_follower)
+		drm_panel_remove_follower(&ihid->panel_follower);
+	else
+		i2c_hid_core_power_down(ihid);
 
 	hid = ihid->hid;
 	hid_destroy_device(hid);
@@ -1171,6 +1245,9 @@ static int i2c_hid_core_pm_suspend(struct device *dev)
 	struct i2c_client *client = to_i2c_client(dev);
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
 
+	if (ihid->is_panel_follower)
+		return 0;
+
 	return i2c_hid_core_suspend(ihid);
 }
 
@@ -1179,6 +1256,9 @@ static int i2c_hid_core_pm_resume(struct device *dev)
 	struct i2c_client *client = to_i2c_client(dev);
 	struct i2c_hid *ihid = i2c_get_clientdata(client);
 
+	if (ihid->is_panel_follower)
+		return 0;
+
 	return i2c_hid_core_resume(ihid);
 }
 
-- 
2.40.1.698.g37aff9b760-goog

Re: [PATCH 7/9] HID: i2c-hid: Support being a panel follower

[Doug Anderson]

Hi,

On Tue, May 23, 2023 at 12:31 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> As talked about in the patch ("drm/panel: Add a way for other devices
> to follow panel state"), we really want to keep the power states of a
> touchscreen and the panel it's attached to in sync with each other. In
> that spirit, add support to i2c-hid to be a panel follower. This will
> let the i2c-hid driver get informed when the panel is powered on and
> off. From there we can match the i2c-hid device's power state to that
> of the panel.
>
> NOTE: this patch specifically _doesn't_ use pm_runtime to keep track
> of / manage the power state of the i2c-hid device, even though my
> first instinct said that would be the way to go. Specific problems
> with using pm_runtime():
> * The initial power up couldn't happen in a runtime resume function
>   since it create sub-devices and, apparently, that's not good to do
>   in your resume function.
> * Managing our power state with pm_runtime meant fighting to make the
>   right thing happen at system suspend to prevent the system from
>   trying to resume us only to suspend us again. While this might be
>   able to be solved, it added complexity.
> Overall the code without pm_runtime() ended up being smaller and
> easier to understand.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
>  drivers/hid/i2c-hid/i2c-hid-core.c | 82 +++++++++++++++++++++++++++++-
>  1 file changed, 81 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
> index 34c0d98b4976..f1bb89377e8d 100644
> --- a/drivers/hid/i2c-hid/i2c-hid-core.c
> +++ b/drivers/hid/i2c-hid/i2c-hid-core.c
> @@ -38,6 +38,8 @@
>  #include <linux/mutex.h>
>  #include <asm/unaligned.h>
>
> +#include <drm/drm_panel.h>
> +
>  #include "../hid-ids.h"
>  #include "i2c-hid.h"
>
> @@ -107,6 +109,8 @@ struct i2c_hid {
>         struct mutex            reset_lock;
>
>         struct i2chid_ops       *ops;
> +       struct drm_panel_follower panel_follower;
> +       bool                    is_panel_follower;
>  };
>
>  static const struct i2c_hid_quirks {
> @@ -1058,6 +1062,34 @@ int i2c_hid_core_initial_power_up(struct i2c_hid *ihid)
>         return ret;
>  }
>
> +int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)

As pointed out by the kernel test robot, I clearly missed making
several functions "static" in this patch series. :( I'll fix that in
v2, but for now I'll hold off sending v2 to wait for additional
feedback.

-Doug

[PATCH 8/9] HID: i2c-hid: Do panel follower work on the system_wq

[Douglas Anderson]

Turning on an i2c-hid device can be a slow process. This is why
i2c-hid devices use PROBE_PREFER_ASYNCHRONOUS. Unfortunately, when
we're a panel follower the i2c-hid power up sequence now blocks the
power on of the panel. Let's fix that by scheduling the work on the
system_wq.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/hid/i2c-hid/i2c-hid-core.c | 42 +++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index f1bb89377e8d..800f0dc6f6cf 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -110,7 +110,9 @@ struct i2c_hid {
 
 	struct i2chid_ops	*ops;
 	struct drm_panel_follower panel_follower;
+	struct work_struct	panel_follower_prepare_work;
 	bool			is_panel_follower;
+	bool			prepare_work_finished;
 };
 
 static const struct i2c_hid_quirks {
@@ -1062,10 +1064,12 @@ int i2c_hid_core_initial_power_up(struct i2c_hid *ihid)
 	return ret;
 }
 
-int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)
+void ihid_core_panel_prepare_work(struct work_struct *work)
 {
-	struct i2c_hid *ihid = container_of(follower, struct i2c_hid, panel_follower);
+	struct i2c_hid *ihid = container_of(work, struct i2c_hid,
+					    panel_follower_prepare_work);
 	struct hid_device *hid = ihid->hid;
+	int ret;
 
 	/*
 	 * hid->version is set on the first power up. If it's still zero then
@@ -1073,15 +1077,44 @@ int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)
 	 * steps.
 	 */
 	if (!hid->version)
-		return i2c_hid_core_initial_power_up(ihid);
+		ret = i2c_hid_core_initial_power_up(ihid);
+	else
+		ret = i2c_hid_core_resume(ihid);
 
-	return i2c_hid_core_resume(ihid);
+	if (ret)
+		dev_warn(&ihid->client->dev, "Power on failed: %d\n", ret);
+	else
+		WRITE_ONCE(ihid->prepare_work_finished, true);
+
+	/* Match with i2c_hid_core_panel_unpreparing() */
+	smp_wmb();
+}
+
+int i2c_hid_core_panel_prepared(struct drm_panel_follower *follower)
+{
+	struct i2c_hid *ihid = container_of(follower, struct i2c_hid, panel_follower);
+
+	/*
+	 * Powering on a touchscreen can be a slow process. Queue the work to
+	 * the system workqueue so we don't block the panel's power up.
+	 */
+	WRITE_ONCE(ihid->prepare_work_finished, false);
+	schedule_work(&ihid->panel_follower_prepare_work);
+
+	return 0;
 }
 
 int i2c_hid_core_panel_unpreparing(struct drm_panel_follower *follower)
 {
 	struct i2c_hid *ihid = container_of(follower, struct i2c_hid, panel_follower);
 
+	cancel_work_sync(&ihid->panel_follower_prepare_work);
+
+	/* Match with ihid_core_panel_prepare_work() */
+	smp_rmb();
+	if (!READ_ONCE(ihid->prepare_work_finished))
+		return 0;
+
 	return i2c_hid_core_suspend(ihid);
 }
 
@@ -1124,6 +1157,7 @@ int i2c_hid_core_probe(struct i2c_client *client, struct i2chid_ops *ops,
 
 	init_waitqueue_head(&ihid->wait);
 	mutex_init(&ihid->reset_lock);
+	INIT_WORK(&ihid->panel_follower_prepare_work, ihid_core_panel_prepare_work);
 
 	/* we need to allocate the command buffer without knowing the maximum
 	 * size of the reports. Let's use HID_MIN_BUFFER_SIZE, then we do the
-- 
2.40.1.698.g37aff9b760-goog

[PATCH 9/9] arm64: dts: qcom: sc7180: Link trogdor touchscreens to the panels

[Douglas Anderson]

Let's provide the proper link from the touchscreen to the panel on
trogdor devices where the touchscreen support it. This allows the OS
to power sequence the touchscreen more properly.

For the most part, this is just expected to marginally improve power
consumption while the screen is off. However, in at least one trogdor
model (wormdingler) it's suspected that this will fix some behavorial
corner cases when the panel power cycles (like for a modeset) without
the touchscreen power cycling.

NOTE: some trogdor variants use touchscreens that don't (yet) support
linking the touchscreen and the panel. Those variants are left alone.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 arch/arm64/boot/dts/qcom/sc7180-trogdor-coachz.dtsi        | 1 +
 arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar.dtsi      | 1 +
 arch/arm64/boot/dts/qcom/sc7180-trogdor-lazor.dtsi         | 1 +
 arch/arm64/boot/dts/qcom/sc7180-trogdor-pompom.dtsi        | 1 +
 arch/arm64/boot/dts/qcom/sc7180-trogdor-quackingstick.dtsi | 1 +
 arch/arm64/boot/dts/qcom/sc7180-trogdor-wormdingler.dtsi   | 1 +
 6 files changed, 6 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-coachz.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor-coachz.dtsi
index 8b8ea8af165d..b4f328d3e1f6 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-coachz.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-coachz.dtsi
@@ -104,6 +104,7 @@ ap_ts: touchscreen@5d {
 		interrupt-parent = <&tlmm>;
 		interrupts = <9 IRQ_TYPE_LEVEL_LOW>;
 
+		panel = <&panel>;
 		reset-gpios = <&tlmm 8 GPIO_ACTIVE_LOW>;
 
 		vdd-supply = <&pp3300_ts>;
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar.dtsi
index b3ba23a88a0b..88aeb415bd5b 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar.dtsi
@@ -116,6 +116,7 @@ ap_ts: touchscreen@14 {
 		interrupt-parent = <&tlmm>;
 		interrupts = <9 IRQ_TYPE_LEVEL_LOW>;
 
+		panel = <&panel>;
 		reset-gpios = <&tlmm 8 GPIO_ACTIVE_LOW>;
 
 		vdd-supply = <&pp3300_touch>;
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-lazor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor-lazor.dtsi
index 269007d73162..c65f18ea3e5c 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-lazor.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-lazor.dtsi
@@ -43,6 +43,7 @@ ap_ts: touchscreen@10 {
 		interrupt-parent = <&tlmm>;
 		interrupts = <9 IRQ_TYPE_LEVEL_LOW>;
 
+		panel = <&panel>;
 		post-power-on-delay-ms = <20>;
 		hid-descr-addr = <0x0001>;
 
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-pompom.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor-pompom.dtsi
index 6c5287bd27d6..d2aafd1ea672 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-pompom.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-pompom.dtsi
@@ -102,6 +102,7 @@ ap_ts: touchscreen@10 {
 		interrupt-parent = <&tlmm>;
 		interrupts = <9 IRQ_TYPE_LEVEL_LOW>;
 
+		panel = <&panel>;
 		post-power-on-delay-ms = <20>;
 		hid-descr-addr = <0x0001>;
 
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-quackingstick.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor-quackingstick.dtsi
index 8e7b42f843d4..0785873d1345 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-quackingstick.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-quackingstick.dtsi
@@ -99,6 +99,7 @@ ap_ts: touchscreen@10 {
 		interrupt-parent = <&tlmm>;
 		interrupts = <9 IRQ_TYPE_LEVEL_LOW>;
 
+		panel = <&panel>;
 		post-power-on-delay-ms = <20>;
 		hid-descr-addr = <0x0001>;
 
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-wormdingler.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor-wormdingler.dtsi
index 262d6691abd9..f70f5b42c845 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-wormdingler.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-wormdingler.dtsi
@@ -154,6 +154,7 @@ ap_ts: touchscreen@1 {
 		interrupt-parent = <&tlmm>;
 		interrupts = <9 IRQ_TYPE_EDGE_FALLING>;
 
+		panel = <&panel>;
 		post-power-on-delay-ms = <70>;
 		hid-descr-addr = <0x0001>;
 
-- 
2.40.1.698.g37aff9b760-goog

Re: [PATCH 0/9] drm/panel and i2c-hid: Allow panels and touchscreens to power sequence together

[Dmitry Torokhov]

Hi Doug,

On Tue, May 23, 2023 at 12:27:54PM -0700, Douglas Anderson wrote:
> 
> The big motivation for this patch series is mostly described in the patch
> ("drm/panel: Add a way for other devices to follow panel state"), but to
> quickly summarize here: for touchscreens that are connected to a panel we
> need the ability to power sequence the two device together. This is not a
> new need, but so far we've managed to get by through a combination of
> inefficiency, added costs, or perhaps just a little bit of brokenness.
> It's time to do better. This patch series allows us to do better.

This seems to grow a new way of building relationship between panels and
associated devices. Can we make device_link_*() work for us?

Thanks.

-- 
Dmitry

Re: [PATCH 0/9] drm/panel and i2c-hid: Allow panels and touchscreens to power sequence together

[Doug Anderson]

Hi,

On Tue, May 23, 2023 at 2:39 PM Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
>
> Hi Doug,
>
> On Tue, May 23, 2023 at 12:27:54PM -0700, Douglas Anderson wrote:
> >
> > The big motivation for this patch series is mostly described in the patch
> > ("drm/panel: Add a way for other devices to follow panel state"), but to
> > quickly summarize here: for touchscreens that are connected to a panel we
> > need the ability to power sequence the two device together. This is not a
> > new need, but so far we've managed to get by through a combination of
> > inefficiency, added costs, or perhaps just a little bit of brokenness.
> > It's time to do better. This patch series allows us to do better.
>
> This seems to grow a new way of building relationship between panels and
> associated devices. Can we make device_link_*() work for us?

If you know of a way to make it work, that'd be great. ...but I don't
_think_ it would be that easy. I haven't spent much time with the
device_link APIs, though, so please correct me if I'm wrong.

I guess my main issue with device_link would be that that ordering
feels backward. Specifically, the device we're acting on (the one
we're turning off and on) is the panel. We typically turn the panel
off and on at times (during a modeset, when the lid is closed, or just
if the system is idle). When this happens we'd like to remove power
from both the panel and the touchscreen. Userspace is just not setup
to power off touchscreens in tandem with the panel and sometimes (like
in the case of a modeset) it might not even know it needs to. With
device_link I believe that the "child" device is in charge of powering
the parent. I think that would mean that to use device_link we'd need
to make the panel be the child of the touchscreen. Then, I guess we'd
tell the touchscreen not to power itself on if it had children and
just wait for a child to power it on? It feels really awkward partly
because the panel doesn't feel like it should be a child of the
touchscreen and partially because it seems weird that the touchscreen
would somehow need to know not to request power for itself when it has
a child.

...if we're willing to accept the backwardness as described above and
we can find a hack to keep the touchscreen from powering itself up,
then I think things could be made to work OK-ish. I can try to
investigate that route if it doesn't feel too ugly. ...oh, except for
another problem. The initial power up of the i2c-hid device would also
be a problem here. I guess with device_link we'd need to put all the
power up work into "runtime resume". The problem is that upon initial
power up we create "HID" sub-devices and (as far as I could tell) you
can't do that during a runtime resume. :( We could put a special case
to power the touchscreen up before the panel at probe time, but that
could have other consequences?

If we don't go with the backwardness then I think we're a bit stuck
with some of the original problems. Specifically it means that unless
userspace knows to turn off the touchscreen that the touchscreen would
force the panel to never be power cycled. There's at least one panel
(the one on sc7180-trogdor-homestar) where that's known to be a
problem. It also means that we're back to drawing extra power if the
touchscreen is left "on" but the panel power is turned off.

Let me know if I'm misunderstanding.

-Doug

Re: [PATCH 0/9] drm/panel and i2c-hid: Allow panels and touchscreens to power sequence together

[Konrad Dybcio]

On 23.05.2023 21:27, Douglas Anderson wrote:
> 
> The big motivation for this patch series is mostly described in the patch
> ("drm/panel: Add a way for other devices to follow panel state"), but to
> quickly summarize here: for touchscreens that are connected to a panel we
> need the ability to power sequence the two device together. This is not a
> new need, but so far we've managed to get by through a combination of
> inefficiency, added costs, or perhaps just a little bit of brokenness.
> It's time to do better. This patch series allows us to do better.
Panels with integrated touchscreens have been shipping in mainstream devices
since at least 2016. Thanks a lot for looking into this!

Konrad
> 
> Assuming that people think this patch series looks OK, we'll have to
> figure out the right way to land it. The panel patches and i2c-hid
> patches will go through very different trees and so either we'll need
> an Ack from one side or the other or someone to create a tag for the
> other tree to pull in. This will _probably_ require the true drm-misc
> maintainers to get involved, not a lowly committer. ;-)
> 
> 
> Douglas Anderson (9):
>   dt-bindings: HID: i2c-hid: Add "panel" property to i2c-hid backed
>     panels
>   drm/panel: Check for already prepared/enabled in drm_panel
>   drm/panel: Add a way for other devices to follow panel state
>   HID: i2c-hid: Switch to SYSTEM_SLEEP_PM_OPS()
>   HID: i2c-hid: Rearrange probe() to power things up later
>   HID: i2c-hid: Make suspend and resume into helper functions
>   HID: i2c-hid: Support being a panel follower
>   HID: i2c-hid: Do panel follower work on the system_wq
>   arm64: dts: qcom: sc7180: Link trogdor touchscreens to the panels
> 
>  .../bindings/input/elan,ekth6915.yaml         |   6 +
>  .../bindings/input/goodix,gt7375p.yaml        |   6 +
>  .../bindings/input/hid-over-i2c.yaml          |   6 +
>  .../boot/dts/qcom/sc7180-trogdor-coachz.dtsi  |   1 +
>  .../dts/qcom/sc7180-trogdor-homestar.dtsi     |   1 +
>  .../boot/dts/qcom/sc7180-trogdor-lazor.dtsi   |   1 +
>  .../boot/dts/qcom/sc7180-trogdor-pompom.dtsi  |   1 +
>  .../qcom/sc7180-trogdor-quackingstick.dtsi    |   1 +
>  .../dts/qcom/sc7180-trogdor-wormdingler.dtsi  |   1 +
>  drivers/gpu/drm/drm_panel.c                   | 194 +++++++++-
>  drivers/hid/i2c-hid/i2c-hid-core.c            | 330 +++++++++++++-----
>  include/drm/drm_panel.h                       |  89 +++++
>  12 files changed, 542 insertions(+), 95 deletions(-)
>