[PATCH v7 0/6] Support running driver's probe for a device powered off

[PATCH v7 0/6] Support running driver's probe for a device powered off

[Sakari Ailus]

Hi all,

These patches enable calling (and finishing) a driver's probe function
without powering on the respective device on busses where the practice is
to power on the device for probe. While it generally is a driver's job to
check the that the device is there, there are cases where it might be
undesirable. (In this case it stems from a combination of hardware design
and user expectations; see below.) The downside with this change is that
if there is something wrong with the device, it will only be found at the
time the device is used. In this case (the camera sensors + EEPROM in a
sensor) I don't see any tangible harm from that though.

An indication both from the driver and the firmware is required to allow
the device's power state to remain off during probe (see the first patch).


The use case is such that there is a privacy LED next to an integrated
user-facing laptop camera, and this LED is there to signal the user that
the camera is recording a video or capturing images. That LED also happens
to be wired to one of the power supplies of the camera, so whenever you
power on the camera, the LED will be lit, whether images are captured from
the camera --- or not. There's no way to implement this differently
without additional software control (allowing of which is itself a
hardware design decision) on most CSI-2-connected camera sensors as they
simply have no pin to signal the camera streaming state.

This is also what happens during driver probe: the camera will be powered
on by the I²C subsystem calling dev_pm_domain_attach() and the device is
already powered on when the driver's own probe function is called. To the
user this visible during the boot process as a blink of the privacy LED,
suggesting that the camera is recording without the user having used an
application to do that. From the end user's point of view the behaviour is
not expected and for someone unfamiliar with internal workings of a
computer surely seems quite suspicious --- even if images are not being
actually captured.

I've tested these on linux-next master. They also apply to Wolfram's
i2c/for-next branch, there's a patch that affects the I²C core changes
here (see below). The patches apart from that apply to Bartosz's
at24/for-next as well as Mauro's linux-media master branch.

since v6 <URL:https://lore.kernel.org/linux-acpi/20200826115432.6103-1-sakari.ailus@linux.intel.com/>:

- Use u32 for the flags field in struct i2c_driver.

- Use acpi_dev_get_property to read the allow-low-power-probe property.

since v5 <URL:https://lore.kernel.org/linux-acpi/20200810142747.12400-1-sakari.ailus@linux.intel.com/>:

- Identify sensors when they're first powered on. In previous versions, if
  this wasn't in probe, it was not done at all.

- Return allow_low_power_probe() only for ACPI devices, i.e. OF systems
  are not affected by these changes.

- Document that I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag only applies to ACPI
  drivers.

- Fix extra regulator_disable in at24 driver's remove function when the
  device was already in low power state.

since v4 <URL:https://lore.kernel.org/linux-acpi/20200121134157.20396-1-sakari.ailus@linux.intel.com/>:

- Rename "probe-low-power" property as "allow-low-power-probe". This is
  taken into account in function and file naming, too.

- Turn probe_low_power field in struct i2c_driver into flags field.

- Rebase on Wolfram's i2c/for-next branch that contains the removal of the
  support for disabling I²C core IRQ mappings (commit
  0c2a34937f7e4c4776bb261114c475392da2355c).

- Change wording for "allow-low-power-probe" property in ACPI
  documentation.

since v3 <URL:https://lore.kernel.org/linux-acpi/20200109154529.19484-1-sakari.ailus@linux.intel.com/T/#t>:

- Rework the 2nd patch based on Rafael's comments

	- Rework description of the ACPI low power state helper function,
	  according to Rafael's text.

	- Rename and rework the same function as
	  acpi_dev_state_low_power().

	- Reflect the changes in commit message as well.

- Added a patch to document the probe-low-power _DSD property.

since v2 <URL:https://patchwork.kernel.org/cover/11114255/>:

- Remove extra CONFIG_PM ifdefs; these are not needed.

- Move the checks for power state hints from drivers/base/dd.c to
  drivers/i2c/i2c-base-core.c; these are I²C devices anyway.

- Move the probe_low_power field from struct device_driver to struct
  i2c_driver.

since v1:

- Rename probe_powered_off struct device field as probe_low_power and
  reflect the similar naming to the patches overall.

- Work with CONFIG_PM disabled, too.

Rajmohan Mani (1):
  media: i2c: imx319: Support probe while the device is off

Sakari Ailus (5):
  i2c: Allow an ACPI driver to manage the device's power state during
    probe
  ACPI: Add a convenience function to tell a device is in low power
    state
  ov5670: Support probe whilst the device is in a low power state
  at24: Support probing while off
  Documentation: ACPI: Document allow-low-power-probe _DSD property

 .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++
 Documentation/firmware-guide/acpi/index.rst   |  1 +
 drivers/acpi/device_pm.c                      | 31 ++++++++
 drivers/i2c/i2c-core-base.c                   | 19 ++++-
 drivers/media/i2c/imx319.c                    | 74 +++++++++++-------
 drivers/media/i2c/ov5670.c                    | 76 +++++++++++--------
 drivers/misc/eeprom/at24.c                    | 43 ++++++-----
 include/linux/acpi.h                          |  5 ++
 include/linux/i2c.h                           | 14 ++++
 9 files changed, 212 insertions(+), 79 deletions(-)
 create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst

-- 
2.20.1

[PATCH v7 1/6] i2c: Allow an ACPI driver to manage the device's power state during probe

[Sakari Ailus]

Enable drivers to tell ACPI that there's no need to power on a device for
probe. Drivers should still perform this by themselves if there's a need
to. In some cases powering on the device during probe is undesirable, and
this change enables a driver to choose what fits best for it.

Add a field called "flags" into struct i2c_driver for driver flags, and a
flag I2C_DRV_FL_ALLOW_LOW_POWER_PROBE to tell a driver supports probe in
low power state.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/i2c/i2c-core-base.c | 19 ++++++++++++++++---
 include/linux/i2c.h         | 14 ++++++++++++++
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 34a9609f256da..da5f6d642bd76 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -436,6 +436,16 @@ static int i2c_smbus_host_notify_to_irq(const struct i2c_client *client)
 	return irq > 0 ? irq : -ENXIO;
 }
 
+static bool allow_low_power_probe(struct device *dev)
+{
+	struct i2c_driver *driver = to_i2c_driver(dev->driver);
+
+	return driver->flags & I2C_DRV_FL_ALLOW_LOW_POWER_PROBE &&
+		!acpi_dev_get_property(ACPI_COMPANION(dev),
+				       "allow-low-power-probe", ACPI_TYPE_ANY,
+				       NULL);
+}
+
 static int i2c_device_probe(struct device *dev)
 {
 	struct i2c_client	*client = i2c_verify_client(dev);
@@ -514,7 +524,8 @@ static int i2c_device_probe(struct device *dev)
 	if (status < 0)
 		goto err_clear_wakeup_irq;
 
-	status = dev_pm_domain_attach(&client->dev, true);
+	status = dev_pm_domain_attach(&client->dev,
+				      !allow_low_power_probe(&client->dev));
 	if (status)
 		goto err_clear_wakeup_irq;
 
@@ -536,7 +547,8 @@ static int i2c_device_probe(struct device *dev)
 	return 0;
 
 err_detach_pm_domain:
-	dev_pm_domain_detach(&client->dev, true);
+	dev_pm_domain_detach(&client->dev,
+			     !allow_low_power_probe(&client->dev));
 err_clear_wakeup_irq:
 	dev_pm_clear_wake_irq(&client->dev);
 	device_init_wakeup(&client->dev, false);
@@ -562,7 +574,8 @@ static int i2c_device_remove(struct device *dev)
 		status = driver->remove(client);
 	}
 
-	dev_pm_domain_detach(&client->dev, true);
+	dev_pm_domain_detach(&client->dev,
+			     !allow_low_power_probe(&client->dev));
 
 	dev_pm_clear_wake_irq(&client->dev);
 	device_init_wakeup(&client->dev, false);
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index fc55ea41d3237..f8c3257a8bb25 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -11,6 +11,7 @@
 #define _LINUX_I2C_H
 
 #include <linux/acpi.h>		/* for acpi_handle */
+#include <linux/bits.h>
 #include <linux/mod_devicetable.h>
 #include <linux/device.h>	/* for struct device */
 #include <linux/sched.h>	/* for completion */
@@ -217,6 +218,16 @@ enum i2c_alert_protocol {
 	I2C_PROTOCOL_SMBUS_HOST_NOTIFY,
 };
 
+/**
+ * enum i2c_driver_flags - Flags for an I2C device driver
+ *
+ * @I2C_DRV_FL_ALLOW_LOW_POWER_PROBE: Let the ACPI driver manage the device's
+ *				      power state during probe and remove
+ */
+enum i2c_driver_flags {
+	I2C_DRV_FL_ALLOW_LOW_POWER_PROBE = BIT(0),
+};
+
 /**
  * struct i2c_driver - represent an I2C device driver
  * @class: What kind of i2c device we instantiate (for detect)
@@ -231,6 +242,7 @@ enum i2c_alert_protocol {
  * @detect: Callback for device detection
  * @address_list: The I2C addresses to probe (for detect)
  * @clients: List of detected clients we created (for i2c-core use only)
+ * @flags: A bitmask of flags defined in &enum i2c_driver_flags
  *
  * The driver.owner field should be set to the module owner of this driver.
  * The driver.name field should be set to the name of this driver.
@@ -289,6 +301,8 @@ struct i2c_driver {
 	int (*detect)(struct i2c_client *client, struct i2c_board_info *info);
 	const unsigned short *address_list;
 	struct list_head clients;
+
+	u32 flags;
 };
 #define to_i2c_driver(d) container_of(d, struct i2c_driver, driver)
 
-- 
2.20.1

[PATCH v7 2/6] ACPI: Add a convenience function to tell a device is in low power state

[Sakari Ailus]

Add a convenience function to tell whether a device is in low power state,
primarily for use in drivers' probe or remove functions on busses where
the custom is to power on the device for the duration of both.

Returns false on non-ACPI systems.

Suggested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/acpi/device_pm.c | 31 +++++++++++++++++++++++++++++++
 include/linux/acpi.h     |  5 +++++
 2 files changed, 36 insertions(+)

diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
index 94d91c67aeaeb..e3c488d4af0d4 100644
--- a/drivers/acpi/device_pm.c
+++ b/drivers/acpi/device_pm.c
@@ -1344,4 +1344,35 @@ int acpi_dev_pm_attach(struct device *dev, bool power_on)
 	return 1;
 }
 EXPORT_SYMBOL_GPL(acpi_dev_pm_attach);
+
+/**
+ * acpi_dev_state_low_power - Check the current ACPI power state of a device.
+ * @dev: Physical device the ACPI power state of which to check
+ *
+ * On a system without ACPI, return false. On a system with ACPI, return true if
+ * the current ACPI power state of the device is not D0, or false otherwise.
+ *
+ * Note that the power state of a device is not well-defined after it has been
+ * passed to acpi_device_set_power() and before that function returns, so it is
+ * not valid to ask for the ACPI power state of the device in that time frame.
+ */
+bool acpi_dev_state_low_power(struct device *dev)
+{
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+	int power_state;
+	int ret;
+
+	if (!adev)
+		return false;
+
+	ret = acpi_device_get_power(adev, &power_state);
+	if (ret) {
+		dev_dbg(dev, "Cannot obtain power state (%d)\n", ret);
+		return false;
+	}
+
+	return power_state != ACPI_STATE_D0;
+}
+EXPORT_SYMBOL_GPL(acpi_dev_state_low_power);
+
 #endif /* CONFIG_PM */
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 1e4cdc6c7ae20..276f6af99779f 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -976,6 +976,7 @@ int acpi_dev_resume(struct device *dev);
 int acpi_subsys_runtime_suspend(struct device *dev);
 int acpi_subsys_runtime_resume(struct device *dev);
 int acpi_dev_pm_attach(struct device *dev, bool power_on);
+bool acpi_dev_state_low_power(struct device *dev);
 #else
 static inline int acpi_dev_runtime_suspend(struct device *dev) { return 0; }
 static inline int acpi_dev_runtime_resume(struct device *dev) { return 0; }
@@ -985,6 +986,10 @@ static inline int acpi_dev_pm_attach(struct device *dev, bool power_on)
 {
 	return 0;
 }
+static inline bool acpi_dev_state_low_power(struct device *dev)
+{
+	return false;
+}
 #endif
 
 #if defined(CONFIG_ACPI) && defined(CONFIG_PM_SLEEP)
-- 
2.20.1

[PATCH v7 3/6] ov5670: Support probe whilst the device is in a low power state

[Sakari Ailus]

Tell ACPI device PM code that the driver supports the device being in a
low power state when the driver's probe function is entered.

Also do identification on the first access of the device, whether in probe
or when starting streaming.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/media/i2c/ov5670.c | 76 +++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 30 deletions(-)

diff --git a/drivers/media/i2c/ov5670.c b/drivers/media/i2c/ov5670.c
index f26252e35e08d..74b0325c22565 100644
--- a/drivers/media/i2c/ov5670.c
+++ b/drivers/media/i2c/ov5670.c
@@ -1832,6 +1832,8 @@ struct ov5670 {
 
 	/* Streaming on/off */
 	bool streaming;
+	/* True if the device has been identified */
+	bool identified;
 };
 
 #define to_ov5670(_sd)	container_of(_sd, struct ov5670, sd)
@@ -2270,6 +2272,32 @@ static int ov5670_get_skip_frames(struct v4l2_subdev *sd, u32 *frames)
 	return 0;
 }
 
+/* Verify chip ID */
+static int ov5670_identify_module(struct ov5670 *ov5670)
+{
+	struct i2c_client *client = v4l2_get_subdevdata(&ov5670->sd);
+	int ret;
+	u32 val;
+
+	if (ov5670->identified)
+		return 0;
+
+	ret = ov5670_read_reg(ov5670, OV5670_REG_CHIP_ID,
+			      OV5670_REG_VALUE_24BIT, &val);
+	if (ret)
+		return ret;
+
+	if (val != OV5670_CHIP_ID) {
+		dev_err(&client->dev, "chip id mismatch: %x!=%x\n",
+			OV5670_CHIP_ID, val);
+		return -ENXIO;
+	}
+
+	ov5670->identified = true;
+
+	return 0;
+}
+
 /* Prepare streaming by writing default values and customized values */
 static int ov5670_start_streaming(struct ov5670 *ov5670)
 {
@@ -2278,6 +2306,10 @@ static int ov5670_start_streaming(struct ov5670 *ov5670)
 	int link_freq_index;
 	int ret;
 
+	ret = ov5670_identify_module(ov5670);
+	if (ret)
+		return ret;
+
 	/* Get out of from software reset */
 	ret = ov5670_write_reg(ov5670, OV5670_REG_SOFTWARE_RST,
 			       OV5670_REG_VALUE_08BIT, OV5670_SOFTWARE_RST);
@@ -2401,27 +2433,6 @@ static int __maybe_unused ov5670_resume(struct device *dev)
 	return 0;
 }
 
-/* Verify chip ID */
-static int ov5670_identify_module(struct ov5670 *ov5670)
-{
-	struct i2c_client *client = v4l2_get_subdevdata(&ov5670->sd);
-	int ret;
-	u32 val;
-
-	ret = ov5670_read_reg(ov5670, OV5670_REG_CHIP_ID,
-			      OV5670_REG_VALUE_24BIT, &val);
-	if (ret)
-		return ret;
-
-	if (val != OV5670_CHIP_ID) {
-		dev_err(&client->dev, "chip id mismatch: %x!=%x\n",
-			OV5670_CHIP_ID, val);
-		return -ENXIO;
-	}
-
-	return 0;
-}
-
 static const struct v4l2_subdev_video_ops ov5670_video_ops = {
 	.s_stream = ov5670_set_stream,
 };
@@ -2456,6 +2467,7 @@ static int ov5670_probe(struct i2c_client *client)
 	struct ov5670 *ov5670;
 	const char *err_msg;
 	u32 input_clk = 0;
+	bool low_power;
 	int ret;
 
 	device_property_read_u32(&client->dev, "clock-frequency", &input_clk);
@@ -2472,11 +2484,14 @@ static int ov5670_probe(struct i2c_client *client)
 	/* Initialize subdev */
 	v4l2_i2c_subdev_init(&ov5670->sd, client, &ov5670_subdev_ops);
 
-	/* Check module identity */
-	ret = ov5670_identify_module(ov5670);
-	if (ret) {
-		err_msg = "ov5670_identify_module() error";
-		goto error_print;
+	low_power = acpi_dev_state_low_power(&client->dev);
+	if (!low_power) {
+		/* Check module identity */
+		ret = ov5670_identify_module(ov5670);
+		if (ret) {
+			err_msg = "ov5670_identify_module() error";
+			goto error_print;
+		}
 	}
 
 	mutex_init(&ov5670->mutex);
@@ -2513,10 +2528,10 @@ static int ov5670_probe(struct i2c_client *client)
 	ov5670->streaming = false;
 
 	/*
-	 * Device is already turned on by i2c-core with ACPI domain PM.
-	 * Enable runtime PM and turn off the device.
+	 * Don't set the device's state to active if it's in a low power state.
 	 */
-	pm_runtime_set_active(&client->dev);
+	if (!low_power)
+		pm_runtime_set_active(&client->dev);
 	pm_runtime_enable(&client->dev);
 	pm_runtime_idle(&client->dev);
 
@@ -2558,7 +2573,7 @@ static const struct dev_pm_ops ov5670_pm_ops = {
 
 #ifdef CONFIG_ACPI
 static const struct acpi_device_id ov5670_acpi_ids[] = {
-	{"INT3479"},
+	{ "INT3479" },
 	{ /* sentinel */ }
 };
 
@@ -2573,6 +2588,7 @@ static struct i2c_driver ov5670_i2c_driver = {
 	},
 	.probe_new = ov5670_probe,
 	.remove = ov5670_remove,
+	.flags = I2C_DRV_FL_ALLOW_LOW_POWER_PROBE,
 };
 
 module_i2c_driver(ov5670_i2c_driver);
-- 
2.20.1

[PATCH v7 4/6] media: i2c: imx319: Support probe while the device is off

[Sakari Ailus]

From: Rajmohan Mani <rajmohan.mani@intel.com>

Tell ACPI device PM code that the driver supports the device being powered
off when the driver's probe function is entered.

Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/media/i2c/imx319.c | 74 +++++++++++++++++++++++---------------
 1 file changed, 45 insertions(+), 29 deletions(-)

diff --git a/drivers/media/i2c/imx319.c b/drivers/media/i2c/imx319.c
index 17c2e4b41221e..6b63bb0abb138 100644
--- a/drivers/media/i2c/imx319.c
+++ b/drivers/media/i2c/imx319.c
@@ -140,6 +140,8 @@ struct imx319 {
 
 	/* Streaming on/off */
 	bool streaming;
+	/* True if the device has been identified */
+	bool identified;
 };
 
 static const struct imx319_reg imx319_global_regs[] = {
@@ -2084,6 +2086,31 @@ imx319_set_pad_format(struct v4l2_subdev *sd,
 	return 0;
 }
 
+/* Verify chip ID */
+static int imx319_identify_module(struct imx319 *imx319)
+{
+	struct i2c_client *client = v4l2_get_subdevdata(&imx319->sd);
+	int ret;
+	u32 val;
+
+	if (imx319->identified)
+		return 0;
+
+	ret = imx319_read_reg(imx319, IMX319_REG_CHIP_ID, 2, &val);
+	if (ret)
+		return ret;
+
+	if (val != IMX319_CHIP_ID) {
+		dev_err(&client->dev, "chip id mismatch: %x!=%x",
+			IMX319_CHIP_ID, val);
+		return -EIO;
+	}
+
+	imx319->identified = true;
+
+	return 0;
+}
+
 /* Start streaming */
 static int imx319_start_streaming(struct imx319 *imx319)
 {
@@ -2091,6 +2118,10 @@ static int imx319_start_streaming(struct imx319 *imx319)
 	const struct imx319_reg_list *reg_list;
 	int ret;
 
+	ret = imx319_identify_module(imx319);
+	if (ret)
+		return ret;
+
 	/* Global Setting */
 	reg_list = &imx319_global_setting;
 	ret = imx319_write_regs(imx319, reg_list->regs, reg_list->num_of_regs);
@@ -2210,26 +2241,6 @@ static int __maybe_unused imx319_resume(struct device *dev)
 	return ret;
 }
 
-/* Verify chip ID */
-static int imx319_identify_module(struct imx319 *imx319)
-{
-	struct i2c_client *client = v4l2_get_subdevdata(&imx319->sd);
-	int ret;
-	u32 val;
-
-	ret = imx319_read_reg(imx319, IMX319_REG_CHIP_ID, 2, &val);
-	if (ret)
-		return ret;
-
-	if (val != IMX319_CHIP_ID) {
-		dev_err(&client->dev, "chip id mismatch: %x!=%x",
-			IMX319_CHIP_ID, val);
-		return -EIO;
-	}
-
-	return 0;
-}
-
 static const struct v4l2_subdev_core_ops imx319_subdev_core_ops = {
 	.subscribe_event = v4l2_ctrl_subdev_subscribe_event,
 	.unsubscribe_event = v4l2_event_subdev_unsubscribe,
@@ -2424,6 +2435,7 @@ static struct imx319_hwcfg *imx319_get_hwcfg(struct device *dev)
 static int imx319_probe(struct i2c_client *client)
 {
 	struct imx319 *imx319;
+	bool low_power;
 	int ret;
 	u32 i;
 
@@ -2436,11 +2448,14 @@ static int imx319_probe(struct i2c_client *client)
 	/* Initialize subdev */
 	v4l2_i2c_subdev_init(&imx319->sd, client, &imx319_subdev_ops);
 
-	/* Check module identity */
-	ret = imx319_identify_module(imx319);
-	if (ret) {
-		dev_err(&client->dev, "failed to find sensor: %d", ret);
-		goto error_probe;
+	low_power = acpi_dev_state_low_power(&client->dev);
+	if (!low_power) {
+		/* Check module identity */
+		ret = imx319_identify_module(imx319);
+		if (ret) {
+			dev_err(&client->dev, "failed to find sensor: %d", ret);
+			goto error_probe;
+		}
 	}
 
 	imx319->hwcfg = imx319_get_hwcfg(&client->dev);
@@ -2493,10 +2508,10 @@ static int imx319_probe(struct i2c_client *client)
 		goto error_media_entity;
 
 	/*
-	 * Device is already turned on by i2c-core with ACPI domain PM.
-	 * Enable runtime PM and turn off the device.
+	 * Don't set the device's state to active if it's in a low power state.
 	 */
-	pm_runtime_set_active(&client->dev);
+	if (!low_power)
+		pm_runtime_set_active(&client->dev);
 	pm_runtime_enable(&client->dev);
 	pm_runtime_idle(&client->dev);
 
@@ -2536,7 +2551,7 @@ static const struct dev_pm_ops imx319_pm_ops = {
 };
 
 static const struct acpi_device_id imx319_acpi_ids[] = {
-	{ "SONY319A" },
+	{ "SONY319A", },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(acpi, imx319_acpi_ids);
@@ -2549,6 +2564,7 @@ static struct i2c_driver imx319_i2c_driver = {
 	},
 	.probe_new = imx319_probe,
 	.remove = imx319_remove,
+	.flags = I2C_DRV_FL_ALLOW_LOW_POWER_PROBE,
 };
 module_i2c_driver(imx319_i2c_driver);
 
-- 
2.20.1

[PATCH v7 5/6] at24: Support probing while off

[Sakari Ailus]

In certain use cases (where the chip is part of a camera module, and the
camera module is wired together with a camera privacy LED), powering on
the device during probe is undesirable. Add support for the at24 to
execute probe while being powered off. For this to happen, a hint in form
of a device property is required from the firmware.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/misc/eeprom/at24.c | 43 +++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 2591c21b2b5d8..a343e55e41126 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -561,6 +561,7 @@ static int at24_probe(struct i2c_client *client)
 	bool i2c_fn_i2c, i2c_fn_block;
 	unsigned int i, num_addresses;
 	struct at24_data *at24;
+	bool low_power;
 	struct regmap *regmap;
 	bool writable;
 	u8 test_byte;
@@ -698,25 +699,30 @@ static int at24_probe(struct i2c_client *client)
 
 	i2c_set_clientdata(client, at24);
 
-	err = regulator_enable(at24->vcc_reg);
-	if (err) {
-		dev_err(dev, "Failed to enable vcc regulator\n");
-		return err;
-	}
+	low_power = acpi_dev_state_low_power(&client->dev);
+	if (!low_power) {
+		err = regulator_enable(at24->vcc_reg);
+		if (err) {
+			dev_err(dev, "Failed to enable vcc regulator\n");
+			return err;
+		}
 
-	/* enable runtime pm */
-	pm_runtime_set_active(dev);
+		pm_runtime_set_active(dev);
+	}
 	pm_runtime_enable(dev);
 
 	/*
-	 * Perform a one-byte test read to verify that the
-	 * chip is functional.
+	 * Perform a one-byte test read to verify that the chip is functional,
+	 * unless powering on the device is to be avoided during probe (i.e.
+	 * it's powered off right now).
 	 */
-	err = at24_read(at24, 0, &test_byte, 1);
-	if (err) {
-		pm_runtime_disable(dev);
-		regulator_disable(at24->vcc_reg);
-		return -ENODEV;
+	if (!low_power) {
+		err = at24_read(at24, 0, &test_byte, 1);
+		if (err) {
+			pm_runtime_disable(dev);
+			regulator_disable(at24->vcc_reg);
+			return -ENODEV;
+		}
 	}
 
 	pm_runtime_idle(dev);
@@ -736,9 +742,11 @@ static int at24_remove(struct i2c_client *client)
 	struct at24_data *at24 = i2c_get_clientdata(client);
 
 	pm_runtime_disable(&client->dev);
-	if (!pm_runtime_status_suspended(&client->dev))
-		regulator_disable(at24->vcc_reg);
-	pm_runtime_set_suspended(&client->dev);
+	if (!acpi_dev_state_low_power(&client->dev)) {
+		if (!pm_runtime_status_suspended(&client->dev))
+			regulator_disable(at24->vcc_reg);
+		pm_runtime_set_suspended(&client->dev);
+	}
 
 	return 0;
 }
@@ -775,6 +783,7 @@ static struct i2c_driver at24_driver = {
 	.probe_new = at24_probe,
 	.remove = at24_remove,
 	.id_table = at24_ids,
+	.flags = I2C_DRV_FL_ALLOW_LOW_POWER_PROBE,
 };
 
 static int __init at24_init(void)
-- 
2.20.1

[PATCH v7 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property

[Sakari Ailus]

Document the probe-low-power _DSD property and how it is used with I²C
drivers.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++++++++++++++
 Documentation/firmware-guide/acpi/index.rst   |  1 +
 2 files changed, 29 insertions(+)
 create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst

diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
new file mode 100644
index 0000000000000..6fcc89162b898
--- /dev/null
+++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
@@ -0,0 +1,28 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================
+Probing I²C devices in low power state
+======================================
+
+Introduction
+============
+
+In some cases it may be preferred to leave certain devices powered off for the
+entire system bootup if powering on these devices has adverse side effects,
+beyond just powering on the said device. Linux recognizes the _DSD property
+"allow-low-power-probe" that can be used for this purpose.
+
+How it works
+============
+
+The property "allow-low-power-probe" boolean property may be used to tell Linux
+that the I²C framework should instruct the kernel ACPI framework to leave the
+device in the low power state. If the driver indicates its support for this by
+setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag in struct i2c_driver.flags
+field and the "allow-low-power-probe" property is present, the device will not
+be powered on for probe.
+
+The downside is that as the device is not powered on, even if there's a problem
+with the device, the driver likely probes just fine but the first user will
+find out the device doesn't work, instead of a failure at probe time. This
+feature should thus be used sparingly.
diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
index ad3b5afdae77e..0070fcde9e669 100644
--- a/Documentation/firmware-guide/acpi/index.rst
+++ b/Documentation/firmware-guide/acpi/index.rst
@@ -11,6 +11,7 @@ ACPI Support
    dsd/graph
    dsd/data-node-references
    dsd/leds
+   dsd/allow-low-power-probe
    enumeration
    osi
    method-customizing
-- 
2.20.1

Re: [PATCH v7 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property

[Rafael J. Wysocki]

On Tue, Sep 1, 2020 at 11:03 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> Document the probe-low-power _DSD property and how it is used with I²C
> drivers.

I would reorder the series to make this go right after the [1/6] or
maybe even fold it into that patch.

The point is that the changes in [1/6] clearly depend on the property
defined here.

> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++++++++++++++
>  Documentation/firmware-guide/acpi/index.rst   |  1 +
>  2 files changed, 29 insertions(+)
>  create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
>
> diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> new file mode 100644
> index 0000000000000..6fcc89162b898
> --- /dev/null
> +++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> @@ -0,0 +1,28 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +======================================
> +Probing I²C devices in low power state
> +======================================
> +
> +Introduction
> +============
> +
> +In some cases it may be preferred to leave certain devices powered off for the
> +entire system bootup if powering on these devices has adverse side effects,
> +beyond just powering on the said device. Linux recognizes the _DSD property
> +"allow-low-power-probe" that can be used for this purpose.

It would be good to refer to the document defining the generic _DSD
properties mechanism and the GUID used for that from here.

The meaning of  "_DSD property" may not be entirely clear to the
reader as it stands.

And maybe call the property "i2c-allow-low-power-probe" or similar, to
indicate that it is specific to i2c.

> +
> +How it works
> +============
> +
> +The property "allow-low-power-probe" boolean property may be used to tell Linux

"boolean device property" ?

> +that the I²C framework should instruct the kernel ACPI framework to leave the
> +device in the low power state. If the driver indicates its support for this by
> +setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag in struct i2c_driver.flags
> +field and the "allow-low-power-probe" property is present, the device will not
> +be powered on for probe.
> +
> +The downside is that as the device is not powered on, even if there's a problem
> +with the device, the driver likely probes just fine but the first user will
> +find out the device doesn't work, instead of a failure at probe time. This
> +feature should thus be used sparingly.

It would be good to give an ASL example with this property provided.

> diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> index ad3b5afdae77e..0070fcde9e669 100644
> --- a/Documentation/firmware-guide/acpi/index.rst
> +++ b/Documentation/firmware-guide/acpi/index.rst
> @@ -11,6 +11,7 @@ ACPI Support
>     dsd/graph
>     dsd/data-node-references
>     dsd/leds
> +   dsd/allow-low-power-probe
>     enumeration
>     osi
>     method-customizing
> --

Re: [PATCH v7 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property

[Sakari Ailus]

Hi Rafael,

Thank you for the review.

On Wed, Sep 02, 2020 at 05:57:01PM +0200, Rafael J. Wysocki wrote:
> On Tue, Sep 1, 2020 at 11:03 PM Sakari Ailus
> <sakari.ailus@linux.intel.com> wrote:
> >
> > Document the probe-low-power _DSD property and how it is used with I²C
> > drivers.
> 
> I would reorder the series to make this go right after the [1/6] or
> maybe even fold it into that patch.
> 
> The point is that the changes in [1/6] clearly depend on the property
> defined here.

Ack.

> 
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > ---
> >  .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++++++++++++++
> >  Documentation/firmware-guide/acpi/index.rst   |  1 +
> >  2 files changed, 29 insertions(+)
> >  create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> >
> > diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > new file mode 100644
> > index 0000000000000..6fcc89162b898
> > --- /dev/null
> > +++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > @@ -0,0 +1,28 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +======================================
> > +Probing I²C devices in low power state
> > +======================================
> > +
> > +Introduction
> > +============
> > +
> > +In some cases it may be preferred to leave certain devices powered off for the
> > +entire system bootup if powering on these devices has adverse side effects,
> > +beyond just powering on the said device. Linux recognizes the _DSD property
> > +"allow-low-power-probe" that can be used for this purpose.
> 
> It would be good to refer to the document defining the generic _DSD
> properties mechanism and the GUID used for that from here.

I'll add a reference to the device properties UUID for _DSD spec.

> 
> The meaning of  "_DSD property" may not be entirely clear to the
> reader as it stands.
> 
> And maybe call the property "i2c-allow-low-power-probe" or similar, to
> indicate that it is specific to i2c.

The bus determines that already, and it's only defined for I²C here. Should
we need this in the future for e.g. I3C, there would be no need to think of
renaming it, just changing the documentation and implementation.

I don't have a strong opinion on that though. 

> 
> > +
> > +How it works
> > +============
> > +
> > +The property "allow-low-power-probe" boolean property may be used to tell Linux
> 
> "boolean device property" ?

Oops. The other "property" was supposed to be removed by now. But yes, I
agree with the suggestion.

> 
> > +that the I²C framework should instruct the kernel ACPI framework to leave the
> > +device in the low power state. If the driver indicates its support for this by
> > +setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag in struct i2c_driver.flags
> > +field and the "allow-low-power-probe" property is present, the device will not
> > +be powered on for probe.
> > +
> > +The downside is that as the device is not powered on, even if there's a problem
> > +with the device, the driver likely probes just fine but the first user will
> > +find out the device doesn't work, instead of a failure at probe time. This
> > +feature should thus be used sparingly.
> 
> It would be good to give an ASL example with this property provided.

I'll add that for v8.

> 
> > diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> > index ad3b5afdae77e..0070fcde9e669 100644
> > --- a/Documentation/firmware-guide/acpi/index.rst
> > +++ b/Documentation/firmware-guide/acpi/index.rst
> > @@ -11,6 +11,7 @@ ACPI Support
> >     dsd/graph
> >     dsd/data-node-references
> >     dsd/leds
> > +   dsd/allow-low-power-probe
> >     enumeration
> >     osi
> >     method-customizing
> > --

-- 
Kind regards,

Sakari Ailus

Re: [PATCH v7 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property

[Rafael J. Wysocki]

On Wed, Sep 2, 2020 at 6:31 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> Hi Rafael,
>
> Thank you for the review.
>
> On Wed, Sep 02, 2020 at 05:57:01PM +0200, Rafael J. Wysocki wrote:
> > On Tue, Sep 1, 2020 at 11:03 PM Sakari Ailus
> > <sakari.ailus@linux.intel.com> wrote:
> > >
> > > Document the probe-low-power _DSD property and how it is used with I²C
> > > drivers.
> >
> > I would reorder the series to make this go right after the [1/6] or
> > maybe even fold it into that patch.
> >
> > The point is that the changes in [1/6] clearly depend on the property
> > defined here.
>
> Ack.
>
> >
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > ---
> > >  .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++++++++++++++
> > >  Documentation/firmware-guide/acpi/index.rst   |  1 +
> > >  2 files changed, 29 insertions(+)
> > >  create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > >
> > > diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > > new file mode 100644
> > > index 0000000000000..6fcc89162b898
> > > --- /dev/null
> > > +++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > > @@ -0,0 +1,28 @@
> > > +.. SPDX-License-Identifier: GPL-2.0
> > > +
> > > +======================================
> > > +Probing I²C devices in low power state
> > > +======================================
> > > +
> > > +Introduction
> > > +============
> > > +
> > > +In some cases it may be preferred to leave certain devices powered off for the
> > > +entire system bootup if powering on these devices has adverse side effects,
> > > +beyond just powering on the said device. Linux recognizes the _DSD property
> > > +"allow-low-power-probe" that can be used for this purpose.
> >
> > It would be good to refer to the document defining the generic _DSD
> > properties mechanism and the GUID used for that from here.
>
> I'll add a reference to the device properties UUID for _DSD spec.
>
> >
> > The meaning of  "_DSD property" may not be entirely clear to the
> > reader as it stands.
> >
> > And maybe call the property "i2c-allow-low-power-probe" or similar, to
> > indicate that it is specific to i2c.
>
> The bus determines that already, and it's only defined for I²C here. Should
> we need this in the future for e.g. I3C, there would be no need to think of
> renaming it, just changing the documentation and implementation.
>
> I don't have a strong opinion on that though.

The point is that the property is not going to be recognized beyond i2c.

> > > +
> > > +How it works
> > > +============
> > > +
> > > +The property "allow-low-power-probe" boolean property may be used to tell Linux
> >
> > "boolean device property" ?
>
> Oops. The other "property" was supposed to be removed by now. But yes, I
> agree with the suggestion.
>
> >
> > > +that the I²C framework should instruct the kernel ACPI framework to leave the
> > > +device in the low power state. If the driver indicates its support for this by
> > > +setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag in struct i2c_driver.flags
> > > +field and the "allow-low-power-probe" property is present, the device will not
> > > +be powered on for probe.
> > > +
> > > +The downside is that as the device is not powered on, even if there's a problem
> > > +with the device, the driver likely probes just fine but the first user will
> > > +find out the device doesn't work, instead of a failure at probe time. This
> > > +feature should thus be used sparingly.
> >
> > It would be good to give an ASL example with this property provided.
>
> I'll add that for v8.
>
> >
> > > diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
> > > index ad3b5afdae77e..0070fcde9e669 100644
> > > --- a/Documentation/firmware-guide/acpi/index.rst
> > > +++ b/Documentation/firmware-guide/acpi/index.rst
> > > @@ -11,6 +11,7 @@ ACPI Support
> > >     dsd/graph
> > >     dsd/data-node-references
> > >     dsd/leds
> > > +   dsd/allow-low-power-probe
> > >     enumeration
> > >     osi
> > >     method-customizing
> > > --
>
> --
> Kind regards,
>
> Sakari Ailus

Re: [PATCH v7 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property

[Sakari Ailus]

On Wed, Sep 02, 2020 at 06:34:30PM +0200, Rafael J. Wysocki wrote:
> On Wed, Sep 2, 2020 at 6:31 PM Sakari Ailus
> <sakari.ailus@linux.intel.com> wrote:
> >
> > Hi Rafael,
> >
> > Thank you for the review.
> >
> > On Wed, Sep 02, 2020 at 05:57:01PM +0200, Rafael J. Wysocki wrote:
> > > On Tue, Sep 1, 2020 at 11:03 PM Sakari Ailus
> > > <sakari.ailus@linux.intel.com> wrote:
> > > >
> > > > Document the probe-low-power _DSD property and how it is used with I²C
> > > > drivers.
> > >
> > > I would reorder the series to make this go right after the [1/6] or
> > > maybe even fold it into that patch.
> > >
> > > The point is that the changes in [1/6] clearly depend on the property
> > > defined here.
> >
> > Ack.
> >
> > >
> > > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > > ---
> > > >  .../acpi/dsd/allow-low-power-probe.rst        | 28 +++++++++++++++++++
> > > >  Documentation/firmware-guide/acpi/index.rst   |  1 +
> > > >  2 files changed, 29 insertions(+)
> > > >  create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > > >
> > > > diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > > > new file mode 100644
> > > > index 0000000000000..6fcc89162b898
> > > > --- /dev/null
> > > > +++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst
> > > > @@ -0,0 +1,28 @@
> > > > +.. SPDX-License-Identifier: GPL-2.0
> > > > +
> > > > +======================================
> > > > +Probing I²C devices in low power state
> > > > +======================================
> > > > +
> > > > +Introduction
> > > > +============
> > > > +
> > > > +In some cases it may be preferred to leave certain devices powered off for the
> > > > +entire system bootup if powering on these devices has adverse side effects,
> > > > +beyond just powering on the said device. Linux recognizes the _DSD property
> > > > +"allow-low-power-probe" that can be used for this purpose.
> > >
> > > It would be good to refer to the document defining the generic _DSD
> > > properties mechanism and the GUID used for that from here.
> >
> > I'll add a reference to the device properties UUID for _DSD spec.
> >
> > >
> > > The meaning of  "_DSD property" may not be entirely clear to the
> > > reader as it stands.
> > >
> > > And maybe call the property "i2c-allow-low-power-probe" or similar, to
> > > indicate that it is specific to i2c.
> >
> > The bus determines that already, and it's only defined for I²C here. Should
> > we need this in the future for e.g. I3C, there would be no need to think of
> > renaming it, just changing the documentation and implementation.
> >
> > I don't have a strong opinion on that though.
> 
> The point is that the property is not going to be recognized beyond i2c.

Not right now, that is true. Sure, I can change it for v8.

-- 
Sakari Ailus