[PATCH v2 0/7] arm64: mediatek: Chromebook trackpad supply fixes

[PATCH v2 0/7] arm64: mediatek: Chromebook trackpad supply fixes

[Chen-Yu Tsai]

Hi everyone,

This series fixes the trackpad descriptions on some MediaTek-based
Chromebooks: either the trackpad's supply was set as always-on to
workaround missing delays in the driver, or the delay and supply
are missing from the trackpad's device node.

v1 was just the first patch [1]. It has since grown to cover multiple
drivers and devices.


Patch 1 adds the correct enable delay after enabling the supply regulator
for the Elan trackpad to initialize. Compared to v1, the delay is now
skipped if the regulator was already enabled to avoid impacting boot
time or time before the trackpad is operational.

Patch 2 applies the same logic of skipping the power on delay to the
i2c-hid-of driver.

Patch 3 applies the same logic of skipping the power on delay to the
i2c OF component prober library.

Patch 4 adds a delay between when the device node found is enabled and
when regulator_disable() is called. This gives an asynchronously probing
driver some time to increment the enable count of their regulator
reference, thus keeping the device operational and allowing the driver
to skip the initialization delay.

Patch 5 adds the correct delay for probing trackpads for Hana devices
to the ChromeOS OF component prober.

Patch 6 removes the "always-on" setting from the trackpad supply for
Elm / Hana and adds the correct delay to the second source trackpad.
This corrects the hardware description.

Patch 7 adds the supply and power on delay properties to the Synaptics
trackpad on the Spherion device. Combined with previous driver changes
this should cause no actual functional changes or delays.


Please take a look. There are no build time dependencies between any
of the patches, but the DT changes must go in after all the driver
changes land, especially the first one adding delays to the Elan
trackpad driver. Otherwise one could potentially end up with a
non-functional trackpad on the device.


Thanks
ChenYu

[1] https://lore.kernel.org/all/20241001093815.2481899-1-wenst@chromium.org/

Chen-Yu Tsai (7):
  Input: elan_i2c - Wait for initialization after enabling regulator
    supply
  HID: i2c-hid-of: skip post-power-on delay if already powered on
  i2c: of-prober: skip post-power-on delay if already powered on
  i2c: of-prober: Defer regulator_disable() on successful probe in
    simple helper
  platform/chrome: of_hw_prober: Add delay for hana trackpads
  arm64: dts: mediatek: mt8173-elm-hana: Unmark trackpad supply as
    always-on
  arm64: dts: mediatek: mt8192-asurada-spherion: Add Synaptics
    trackpad's supply

 .../boot/dts/mediatek/mt8173-elm-hana.dtsi    |  8 +----
 arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi  |  1 -
 .../mediatek/mt8192-asurada-spherion-r0.dts   |  2 ++
 drivers/hid/i2c-hid/i2c-hid-of.c              |  8 ++++-
 drivers/i2c/i2c-core-of-prober.c              | 29 +++++++++++++++----
 drivers/input/mouse/elan_i2c_core.c           | 13 +++++++++
 .../platform/chrome/chromeos_of_hw_prober.c   |  4 +--
 7 files changed, 48 insertions(+), 17 deletions(-)

-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v2 1/7] Input: elan_i2c - Wait for initialization after enabling regulator supply

[Chen-Yu Tsai]

Elan trackpad controllers require some delay after enabling power to
the controller for the hardware and firmware to initialize:

  - 2ms for hardware initialization
  - 100ms for firmware initialization

Until then, the hardware will not respond to I2C transfers. This was
observed on the MT8173 Chromebooks after the regulator supply for the
trackpad was changed to "not always on".

Add proper delays after regulator_enable() calls. To avoid impacting
the boot time of existing devices that have the power rails always on,
skip the delay if the regulator supply was already enabled. In this
case the regulator is either always on, was on by default at power up,
or was left on by some other driver, such as the I2C OF component
prober. Either way the controller has had ample time to initialize.

Fixes: 6696777c6506 ("Input: add driver for Elan I2C/SMbus touchpad")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
Changes since v1:
- Delay only if the regulator was previously disabled / turned off
- Link to v1
  https://lore.kernel.org/all/20241001093815.2481899-1-wenst@chromium.org/
---
 drivers/input/mouse/elan_i2c_core.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c
index f93dd545d66b..db48d7ef8357 100644
--- a/drivers/input/mouse/elan_i2c_core.c
+++ b/drivers/input/mouse/elan_i2c_core.c
@@ -47,6 +47,8 @@
 #define ETP_FWIDTH_REDUCE	90
 #define ETP_FINGER_WIDTH	15
 #define ETP_RETRY_COUNT		3
+/* H/W init 2 ms + F/W init 100 ms w/ round up */
+#define ETP_POWER_ON_DELAY	110
 
 /* quirks to control the device */
 #define ETP_QUIRK_QUICK_WAKEUP	BIT(0)
@@ -1219,6 +1221,7 @@ static int elan_probe(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	struct elan_tp_data *data;
 	unsigned long irqflags;
+	bool supply_was_enabled;
 	int error;
 
 	if (IS_ENABLED(CONFIG_MOUSE_ELAN_I2C_I2C) &&
@@ -1250,6 +1253,8 @@ static int elan_probe(struct i2c_client *client)
 	if (IS_ERR(data->vcc))
 		return dev_err_probe(dev, PTR_ERR(data->vcc), "Failed to get 'vcc' regulator\n");
 
+	supply_was_enabled = regulator_is_enabled(data->vcc);
+
 	error = regulator_enable(data->vcc);
 	if (error) {
 		dev_err(dev, "Failed to enable regulator: %d\n", error);
@@ -1263,6 +1268,9 @@ static int elan_probe(struct i2c_client *client)
 		return error;
 	}
 
+	if (!supply_was_enabled)
+		msleep(ETP_POWER_ON_DELAY);
+
 	/* Make sure there is something at this address */
 	error = i2c_smbus_read_byte(client);
 	if (error < 0) {
@@ -1406,11 +1414,16 @@ static int elan_resume(struct device *dev)
 	int error;
 
 	if (!device_may_wakeup(dev)) {
+		bool supply_was_enabled = regulator_is_enabled(data->vcc);
+
 		error = regulator_enable(data->vcc);
 		if (error) {
 			dev_err(dev, "error %d enabling regulator\n", error);
 			goto err;
 		}
+
+		if (!supply_was_enabled)
+			msleep(ETP_POWER_ON_DELAY);
 	}
 
 	error = elan_set_power(data, true);
-- 
2.55.0.rc0.799.gd6f94ed593-goog

Re: [PATCH v2 1/7] Input: elan_i2c - Wait for initialization after enabling regulator supply

[Dmitry Torokhov]

Hi Chen-Yu,

On Fri, Jul 03, 2026 at 07:55:54PM +0800, Chen-Yu Tsai wrote:
> Elan trackpad controllers require some delay after enabling power to
> the controller for the hardware and firmware to initialize:
> 
>   - 2ms for hardware initialization
>   - 100ms for firmware initialization
> 
> Until then, the hardware will not respond to I2C transfers. This was
> observed on the MT8173 Chromebooks after the regulator supply for the
> trackpad was changed to "not always on".
> 
> Add proper delays after regulator_enable() calls. To avoid impacting
> the boot time of existing devices that have the power rails always on,
> skip the delay if the regulator supply was already enabled. In this
> case the regulator is either always on, was on by default at power up,
> or was left on by some other driver, such as the I2C OF component
> prober. Either way the controller has had ample time to initialize.

Unfortunately we do not know that [it had ample time]. For this code be
reliable we need to record the time at which given regulator was turned
on and then execute/adjust the delay as needed. Until we have it we need
to assume the regulator was enabled at the time of regulator_enable()
call.

I am not concerned with increased boot time too much given the driver is
set up for asynchronous probing.

Thanks.

-- 
Dmitry

[PATCH v2 2/7] HID: i2c-hid-of: skip post-power-on delay if already powered on

[Chen-Yu Tsai]

On some devices the HID device is powered from an always-on power rail,
or the power rail has been left on by either POR defaults or the
bootloader. By the time the driver probes, the device most certainly
has finished initializing. There is no need for the delay.

In such designs, the system integrators tend to work around the delay
to avoid the boot time penalty by simply omitting it from the device
tree. This is undesired, as the device tree is not fully describing
the hardware.

Instead, check if the regulator supplies are all enabled, and skip
the post-power-on delay if that is the case.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 drivers/hid/i2c-hid/i2c-hid-of.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-of.c b/drivers/hid/i2c-hid/i2c-hid-of.c
index 59393d71ddb9..70afdfb207ac 100644
--- a/drivers/hid/i2c-hid/i2c-hid-of.c
+++ b/drivers/hid/i2c-hid/i2c-hid-of.c
@@ -29,6 +29,7 @@
 #include <linux/of.h>
 #include <linux/pm.h>
 #include <linux/regulator/consumer.h>
+#include <linux/string_choices.h>
 
 #include "i2c-hid.h"
 
@@ -46,8 +47,12 @@ static int i2c_hid_of_power_up(struct i2chid_ops *ops)
 {
 	struct i2c_hid_of *ihid_of = container_of(ops, struct i2c_hid_of, ops);
 	struct device *dev = &ihid_of->client->dev;
+	bool supply_was_enabled = true;
 	int ret;
 
+	for (unsigned int i = 0; i < ARRAY_SIZE(ihid_of->supplies); i++)
+		supply_was_enabled &= regulator_is_enabled(ihid_of->supplies[i].consumer);
+
 	ret = regulator_bulk_enable(ARRAY_SIZE(ihid_of->supplies),
 				    ihid_of->supplies);
 	if (ret) {
@@ -55,7 +60,8 @@ static int i2c_hid_of_power_up(struct i2chid_ops *ops)
 		return ret;
 	}
 
-	if (ihid_of->post_power_delay_ms)
+	dev_dbg(dev, "supply was %s.\n", str_on_off(supply_was_enabled));
+	if (!supply_was_enabled && ihid_of->post_power_delay_ms)
 		msleep(ihid_of->post_power_delay_ms);
 
 	gpiod_set_value_cansleep(ihid_of->reset_gpio, 0);
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v2 3/7] i2c: of-prober: skip post-power-on delay if already powered on

[Chen-Yu Tsai]

On some devices the I2C component is powered from an always-on power
rail, or the power rail has been left on by either POR defaults or
the bootloader. By the time the prober probes the device, the device
most certainly has finished initializing and can respond. There is no
need for the delay.

In such designs, the system integrators tend to work around the delay
to avoid the boot time penalty by simply omitting it from the device
tree and the component prober. This is undesired, as the device tree
is not fully describing the hardware.

Instead, check if the regulator supplies are all enabled, and skip
the post-power-on delay if that is the case.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 drivers/i2c/i2c-core-of-prober.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-core-of-prober.c b/drivers/i2c/i2c-core-of-prober.c
index 6a82b03809d4..f274e260353c 100644
--- a/drivers/i2c/i2c-core-of-prober.c
+++ b/drivers/i2c/i2c-core-of-prober.c
@@ -18,6 +18,7 @@
 #include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 #include <linux/stddef.h>
+#include <linux/string_choices.h>
 
 /*
  * Some devices, such as Google Hana Chromebooks, are produced by multiple
@@ -219,19 +220,25 @@ static void i2c_of_probe_simple_put_supply(struct i2c_of_probe_simple_ctx *ctx)
 
 static int i2c_of_probe_simple_enable_regulator(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
 {
+	bool supply_was_on;
 	int ret;
 
 	if (!ctx->supply)
 		return 0;
 
-	dev_dbg(dev, "Enabling regulator supply \"%s\"\n", ctx->opts->supply_name);
+	supply_was_on = regulator_is_enabled(ctx->supply);
+
+	dev_dbg(dev, "Enabling regulator supply \"%s\" (was %s)\n", ctx->opts->supply_name,
+		str_on_off(supply_was_on));
 
 	ret = regulator_enable(ctx->supply);
 	if (ret)
 		return ret;
 
-	if (ctx->opts->post_power_on_delay_ms)
+	if (!supply_was_on && ctx->opts->post_power_on_delay_ms) {
+		dev_dbg(dev, "Waiting after enabling regulator\n");
 		msleep(ctx->opts->post_power_on_delay_ms);
+	}
 
 	return 0;
 }
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v2 4/7] i2c: of-prober: Defer regulator_disable() on successful probe in simple helper

[Chen-Yu Tsai]

When a I2C component is found, it's device node is immediately enabled.
This triggers device creation and driver binding. The prober will hold
the regulator enable reference across this part. If the driver probes
synchronously, then it happens within this window. On the other hand,
if the driver probes asynchronously, there is high chance that it
happens after the prober's cleanup function was called, in which case
the regulator would have been disabled when the driver's probe function
is called. This would then require the driver to wait 100 ms for the
hardware to reinitialize, even if the probe function was just a split
second late and the regulator was disabled a few milliseconds ago.

Recently, some of the drivers for the component that are targeted by the
I2C OF component prober gained the ability to skip waiting for hardware
initialization if the regulator was left enabled. This happens when the
PMIC has them on by default, or if the component prober left them on
after probing the component.

Wait a bit of time before dropping the enable refcount on our end so
that the actual driver has the opportunity to catch and increase the
refcount on their end. The 100 ms delay was arbitrarily chosen.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 drivers/i2c/i2c-core-of-prober.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-of-prober.c b/drivers/i2c/i2c-core-of-prober.c
index f274e260353c..17495125467e 100644
--- a/drivers/i2c/i2c-core-of-prober.c
+++ b/drivers/i2c/i2c-core-of-prober.c
@@ -243,11 +243,23 @@ static int i2c_of_probe_simple_enable_regulator(struct device *dev, struct i2c_o
 	return 0;
 }
 
-static void i2c_of_probe_simple_disable_regulator(struct device *dev, struct i2c_of_probe_simple_ctx *ctx)
+static void i2c_of_probe_simple_disable_regulator(struct device *dev,
+						  struct i2c_of_probe_simple_ctx *ctx,
+						  bool defer_disable)
 {
 	if (!ctx->supply)
 		return;
 
+	/*
+	 * Wait a bit of time for async drivers to probe and increase the
+	 * regulator enable count. This allows the drivers to check and
+	 * skip waiting for re-initialization.
+	 */
+	if (defer_disable) {
+		dev_dbg(dev, "Deferring regulator disable\n");
+		msleep(100);
+	}
+
 	dev_dbg(dev, "Disabling regulator supply \"%s\"\n", ctx->opts->supply_name);
 
 	regulator_disable(ctx->supply);
@@ -364,7 +376,7 @@ int i2c_of_probe_simple_enable(struct device *dev, struct device_node *bus_node,
 	return 0;
 
 out_disable_regulator:
-	i2c_of_probe_simple_disable_regulator(dev, ctx);
+	i2c_of_probe_simple_disable_regulator(dev, ctx, false);
 out_put_gpiod:
 	i2c_of_probe_simple_put_gpiod(ctx);
 out_put_supply:
@@ -409,7 +421,7 @@ void i2c_of_probe_simple_cleanup(struct device *dev, void *data)
 	i2c_of_probe_simple_disable_gpio(dev, ctx);
 	i2c_of_probe_simple_put_gpiod(ctx);
 
-	i2c_of_probe_simple_disable_regulator(dev, ctx);
+	i2c_of_probe_simple_disable_regulator(dev, ctx, true);
 	i2c_of_probe_simple_put_supply(ctx);
 }
 EXPORT_SYMBOL_NS_GPL(i2c_of_probe_simple_cleanup, "I2C_OF_PROBER");
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v2 5/7] platform/chrome: of_hw_prober: Add delay for hana trackpads

[Chen-Yu Tsai]

Up until now, the MT8173 elm/hana device tree has set the dedicated
regulator supplying the trackpad as always-on, simply because the Elan
driver was missing proper delays. As a result the delay for the
Synaptics trackpad was also omitted, as it was not strictly required
under such a model and delayed the availability of the trackpad to the
user.

The Elan driver recently gained proper delays after power-up, with
adaptive skipping of the delay if the regulator was originally
on. The I2C HID driver and I2C OF component prober library gained
similar adaptive delay skipping. The device tree will be fixed to have
the regulator not be always on, and proper post-power-on delay time
added to the I2C HID device.

Also add the post-power-on delay to the ChromeOS OF component prober,
so that if the regulator is off at the time of probing, the prober knows
to wait for the hardware to initialize.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 drivers/platform/chrome/chromeos_of_hw_prober.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/platform/chrome/chromeos_of_hw_prober.c b/drivers/platform/chrome/chromeos_of_hw_prober.c
index 8562a0e89dc6..54d8941617e2 100644
--- a/drivers/platform/chrome/chromeos_of_hw_prober.c
+++ b/drivers/platform/chrome/chromeos_of_hw_prober.c
@@ -70,10 +70,8 @@ static const struct chromeos_i2c_probe_data chromeos_i2c_probe_hana_trackpad = {
 		/*
 		 * ELAN trackpad needs 2 ms for H/W init and 100 ms for F/W init.
 		 * Synaptics trackpad needs 100 ms.
-		 * However, the regulator is set to "always-on", presumably to
-		 * avoid this delay. The ELAN driver is also missing delays.
 		 */
-		.post_power_on_delay_ms = 0,
+		.post_power_on_delay_ms = 110,
 	},
 };
 
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v2 6/7] arm64: dts: mediatek: mt8173-elm-hana: Unmark trackpad supply as always-on

[Chen-Yu Tsai]

Up until now, the MT8173 elm/hana device tree has set the dedicated
regulator supplying the trackpad as always-on, simply because the Elan
driver was missing proper delays. As a result the delay for the
Synaptics trackpad was also omitted, as it was not strictly required
under such a model and delayed the availability of the trackpad to the
user.

The Elan driver recently gained proper delays after power up, with
opportunistic skipping of the delay when the regulator was originally
on. The I2C HID driver gained similar opportunistic delay skipping.
So has the I2C OF component prober library.

Now fix the device tree to have the regulator not be always on, and
let the I2C HID device have the correct post-power-on delay time.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 arch/arm64/boot/dts/mediatek/mt8173-elm-hana.dtsi | 8 +-------
 arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi      | 1 -
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/arm64/boot/dts/mediatek/mt8173-elm-hana.dtsi b/arch/arm64/boot/dts/mediatek/mt8173-elm-hana.dtsi
index 1004eb8ea52c..b9e311fcd9a0 100644
--- a/arch/arm64/boot/dts/mediatek/mt8173-elm-hana.dtsi
+++ b/arch/arm64/boot/dts/mediatek/mt8173-elm-hana.dtsi
@@ -62,13 +62,7 @@ trackpad2: trackpad@2c {
 		pinctrl-0 = <&trackpad_irq>;
 		reg = <0x2c>;
 		hid-descr-addr = <0x0020>;
-		/*
-		 * The trackpad needs a post-power-on delay of 100ms,
-		 * but at time of writing, the power supply for it on
-		 * this board is always on. The delay is therefore not
-		 * added to avoid impacting the readiness of the
-		 * trackpad.
-		 */
+		post-power-on-delay-ms = <100>;
 		vdd-supply = <&mt6397_vgp6_reg>;
 		wakeup-source;
 		status = "fail-needs-probe";
diff --git a/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi b/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi
index a0573bc359fb..6b9f47f515c7 100644
--- a/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi
+++ b/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi
@@ -1093,7 +1093,6 @@ mt6397_vgp6_reg: ldo_vgp6 {
 				regulator-min-microvolt = <3300000>;
 				regulator-max-microvolt = <3300000>;
 				regulator-enable-ramp-delay = <218>;
-				regulator-always-on;
 			};
 
 			mt6397_vibr_reg: ldo_vibr {
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v2 7/7] arm64: dts: mediatek: mt8192-asurada-spherion: Add Synaptics trackpad's supply

[Chen-Yu Tsai]

The Synaptics trackpad, like the Elan trackpad option, is fed from the
system 3.3V power rail. Add it to the trackpad device node.

Also add the correct post-power-on delay, even though in practice it is
not required. The Synaptics trackpad requires 100ms after power-on (or
deasserting the reset, whichever comes later) to fully initialize. The
power is always on and the reset pin is not routed out, so the
implementation could try skipping the delay.

Cc: <stable+noautosel@kernel.org> # Without driver changes only lengthens probe time
Fixes: 925ebc0cd55c ("arm64: dts: mt8192-asurada-spherion: Add Synaptics trackpad support")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
I think this shouldn't be backported, as backporting it without the
driver enhancements just delays the trackpad probing with no real
gains.
---
 arch/arm64/boot/dts/mediatek/mt8192-asurada-spherion-r0.dts | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada-spherion-r0.dts b/arch/arm64/boot/dts/mediatek/mt8192-asurada-spherion-r0.dts
index 163960f58db5..147a8e9a3a71 100644
--- a/arch/arm64/boot/dts/mediatek/mt8192-asurada-spherion-r0.dts
+++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada-spherion-r0.dts
@@ -90,6 +90,8 @@ trackpad@2c {
 		hid-descr-addr = <0x20>;
 		interrupts-extended = <&pio 15 IRQ_TYPE_LEVEL_LOW>;
 		wakeup-source;
+		vdd-supply = <&pp3300_u>;
+		post-power-on-delay-ms = <100>;
 		status = "fail-needs-probe";
 	};
 };
-- 
2.55.0.rc0.799.gd6f94ed593-goog