[PATCH 7/8] i2c: core: Add function for finding the bus speed from ACPI, take 2

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

ACPI 5 specification doesn't have property for the I2C bus speed but
I2cSerialBus resource descriptor which define each controller-slave
connection define the maximum speed supported by that connection.

Thus finding the maximum safe speed for the bus is to walk through all
I2cSerialBus resources that are associated to I2C controller and use the
speed of slowest connection.

Add function i2c_acpi_find_bus_speed() to the i2c-core that adapter
drivers can call prior registering itself to core.

This implies two-step walk through the I2cSerialBus resources: call to
i2c_acpi_find_bus_speed() does the first scan and finds the safe bus
speed that adapter drivers can set up. Adapter driver registration does
the second scan when i2c-core creates the I2C slaves by calling the
i2c_acpi_register_devices(). In that way the bus speed is set in case
slave device probe gets called during registration and does communication.

Previous version commit 55d38d060e99 ("i2c: core: Add function for finding
the bus speed from ACPI") got reverted due merge conflicts from
commit 525e6fabeae2 ("i2c / ACPI: add support for ACPI reconfigure
notifications").

This version is a bit bigger than previous version but is still sharing
the lowest and complicated part of I2cSerialBus lookup routines with the
existing code.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
---
 drivers/i2c/i2c-core.c | 99 ++++++++++++++++++++++++++++++++++++++++++++------
 include/linux/i2c.h    |  9 +++++
 2 files changed, 97 insertions(+), 11 deletions(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index ac8aee255f9c..c61c961cf8f9 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -107,6 +107,9 @@ struct i2c_acpi_lookup {
 	struct i2c_board_info *info;
 	acpi_handle adapter_handle;
 	acpi_handle device_handle;
+	acpi_handle search_handle;
+	u32 speed;
+	u32 min_speed;
 };
 
 static int i2c_acpi_fill_info(struct acpi_resource *ares, void *data)
@@ -130,19 +133,18 @@ static int i2c_acpi_fill_info(struct acpi_resource *ares, void *data)
 		return 1;
 
 	info->addr = sb->slave_address;
+	lookup->speed = sb->connection_speed;
 	if (sb->access_mode == ACPI_I2C_10BIT_MODE)
 		info->flags |= I2C_CLIENT_TEN;
 
 	return 1;
 }
 
-static int i2c_acpi_get_info(struct acpi_device *adev,
-			     struct i2c_board_info *info,
-			     acpi_handle *adapter_handle)
+static int i2c_acpi_do_lookup(struct acpi_device *adev,
+			      struct i2c_acpi_lookup *lookup)
 {
+	struct i2c_board_info *info = lookup->info;
 	struct list_head resource_list;
-	struct resource_entry *entry;
-	struct i2c_acpi_lookup lookup;
 	int ret;
 
 	if (acpi_bus_get_status(adev) || !adev->status.present ||
@@ -150,24 +152,41 @@ static int i2c_acpi_get_info(struct acpi_device *adev,
 		return -EINVAL;
 
 	memset(info, 0, sizeof(*info));
-	info->fwnode = acpi_fwnode_handle(adev);
-
-	memset(&lookup, 0, sizeof(lookup));
-	lookup.device_handle = acpi_device_handle(adev);
-	lookup.info = info;
+	lookup->device_handle = acpi_device_handle(adev);
 
 	/* Look up for I2cSerialBus resource */
 	INIT_LIST_HEAD(&resource_list);
 	ret = acpi_dev_get_resources(adev, &resource_list,
-				     i2c_acpi_fill_info, &lookup);
+				     i2c_acpi_fill_info, lookup);
 	acpi_dev_free_resource_list(&resource_list);
 
 	if (ret < 0 || !info->addr)
 		return -EINVAL;
 
+	return 0;
+}
+
+static int i2c_acpi_get_info(struct acpi_device *adev,
+			     struct i2c_board_info *info,
+			     acpi_handle *adapter_handle)
+{
+	struct list_head resource_list;
+	struct resource_entry *entry;
+	struct i2c_acpi_lookup lookup;
+	int ret;
+
+	memset(&lookup, 0, sizeof(lookup));
+	lookup.info = info;
+
+	ret = i2c_acpi_do_lookup(adev, &lookup);
+	if (ret)
+		return ret;
+
+	info->fwnode = acpi_fwnode_handle(adev);
 	*adapter_handle = lookup.adapter_handle;
 
 	/* Then fill IRQ number if any */
+	INIT_LIST_HEAD(&resource_list);
 	ret = acpi_dev_get_resources(adev, &resource_list, NULL, NULL);
 	if (ret < 0)
 		return -EINVAL;
@@ -248,6 +267,64 @@ static void i2c_acpi_register_devices(struct i2c_adapter *adap)
 		dev_warn(&adap->dev, "failed to enumerate I2C slaves\n");
 }
 
+static acpi_status i2c_acpi_lookup_speed(acpi_handle handle, u32 level,
+					   void *data, void **return_value)
+{
+	struct i2c_acpi_lookup *lookup = data;
+	struct acpi_device *adev;
+
+	if (acpi_bus_get_device(handle, &adev))
+		return AE_OK;
+
+	if (i2c_acpi_do_lookup(adev, lookup))
+		return AE_OK;
+
+	if (lookup->search_handle != lookup->adapter_handle)
+		return AE_OK;
+
+	if (lookup->speed <= lookup->min_speed)
+		lookup->min_speed = lookup->speed;
+
+	return AE_OK;
+}
+
+/**
+ * i2c_acpi_find_bus_speed - find I2C bus speed from ACPI
+ * @dev: The device owning the bus
+ *
+ * Find the I2C bus speed by walking the ACPI namespace for all I2C slaves
+ * devices connected to this bus and use the speed of slowest device.
+ *
+ * Returns the speed in Hz or zero
+ */
+u32 i2c_acpi_find_bus_speed(struct device *dev)
+{
+	struct i2c_acpi_lookup lookup;
+	struct i2c_board_info dummy;
+	acpi_status status;
+
+	if (!has_acpi_companion(dev))
+		return 0;
+
+	memset(&lookup, 0, sizeof(lookup));
+	lookup.search_handle = ACPI_HANDLE(dev);
+	lookup.min_speed = UINT_MAX;
+	lookup.info = &dummy;
+
+	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
+				     I2C_ACPI_MAX_SCAN_DEPTH,
+				     i2c_acpi_lookup_speed, NULL,
+				     &lookup, NULL);
+
+	if (ACPI_FAILURE(status)) {
+		dev_warn(dev, "unable to find I2C bus speed from ACPI\n");
+		return 0;
+	}
+
+	return lookup.min_speed != UINT_MAX ? lookup.min_speed : 0;
+}
+EXPORT_SYMBOL_GPL(i2c_acpi_find_bus_speed);
+
 static int i2c_acpi_match_adapter(struct device *dev, void *data)
 {
 	struct i2c_adapter *adapter = i2c_verify_adapter(dev);
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index fffdc270ca18..5cde08719fb6 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -766,4 +766,13 @@ static inline struct i2c_adapter *of_get_i2c_adapter_by_node(struct device_node
 }
 #endif /* CONFIG_OF */
 
+#if IS_ENABLED(CONFIG_ACPI)
+u32 i2c_acpi_find_bus_speed(struct device *dev);
+#else
+static inline u32 i2c_acpi_find_bus_speed(struct device *dev)
+{
+	return 0;
+}
+#endif /* CONFIG_ACPI */
+
 #endif /* _LINUX_I2C_H */
-- 
2.8.1