drm/i915/dsi: Parse the I2C element from the VBT MIPI sequence block (v3)

Parsing the i2c element is mainly done to transfer the payload from the
MIPI sequence block to the relevant slave device. In some cases, the
commands that are part of the payload can be used to turn on the backlight.

This patch is actually a refactored version of this old patch:
https://lists.freedesktop.org/archives/intel-gfx/2014-December/056897.html

In addition to the refactoring, the original patch is augmented by
looking up the i2c bus from ACPI NS instead of relying on the bus number
provided in the VBT.

This patch was tested on Aava Mobile's Inari 10 tablet. It enabled
turning on the backlight by transferring the payload to the device.

v2:
- Add DRM_DEV_ERROR for invalid adapter and failed transfer and also
  drop the DRM_DEBUG that existed originally. (Hans)
- Add two gotos instead of one to clean things up properly.

v3:
- Identify the device on which this patch was tested in the commit
  message (Ville)

Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Nabendu Maiti <nabendu.bikash.maiti@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Bob Paauwe <bob.j.paauwe@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200110181123.14536-1-vivek.kasireddy@intel.com

drivers/gpu/drm/i915/display/intel_dsi.h

@@ -69,6 +69,9 @@ struct intel_dsi {
 	/* number of DSI lanes */
 	unsigned int lane_count;
 
+	/* i2c bus associated with the slave device */
+	int i2c_bus_num;
+
 	/*
 	 * video mode pixel format
 	 *

drivers/gpu/drm/i915/display/intel_dsi_vbt.c

@@ -86,6 +86,12 @@ static struct gpio_map vlv_gpio_table[] = {
 	{ VLV_GPIO_NC_11_PANEL1_BKLTCTL },
 };
 
+struct i2c_adapter_lookup {
+	u16 slave_addr;
+	struct intel_dsi *intel_dsi;
+	acpi_handle dev_handle;
+};
+
 #define CHV_GPIO_IDX_START_N		0
 #define CHV_GPIO_IDX_START_E		73
 #define CHV_GPIO_IDX_START_SW		100
@@ -378,11 +384,98 @@ static const u8 *mipi_exec_gpio(struct intel_dsi *intel_dsi, const u8 *data)
 	return data;
 }
 
+static int i2c_adapter_lookup(struct acpi_resource *ares, void *data)
+{
+	struct i2c_adapter_lookup *lookup = data;
+	struct intel_dsi *intel_dsi = lookup->intel_dsi;
+	struct acpi_resource_i2c_serialbus *sb;
+	struct i2c_adapter *adapter;
+	acpi_handle adapter_handle;
+	acpi_status status;
+
+	if (intel_dsi->i2c_bus_num >= 0 ||
+	    !i2c_acpi_get_i2c_resource(ares, &sb))
+		return 1;
+
+	if (lookup->slave_addr != sb->slave_address)
+		return 1;
+
+	status = acpi_get_handle(lookup->dev_handle,
+				 sb->resource_source.string_ptr,
+				 &adapter_handle);
+	if (ACPI_FAILURE(status))
+		return 1;
+
+	adapter = i2c_acpi_find_adapter_by_handle(adapter_handle);
+	if (adapter)
+		intel_dsi->i2c_bus_num = adapter->nr;
+
+	return 1;
+}
+
 static const u8 *mipi_exec_i2c(struct intel_dsi *intel_dsi, const u8 *data)
 {
-	DRM_DEBUG_KMS("Skipping I2C element execution\n");
+	struct drm_device *drm_dev = intel_dsi->base.base.dev;
+	struct device *dev = &drm_dev->pdev->dev;
+	struct i2c_adapter *adapter;
+	struct acpi_device *acpi_dev;
+	struct list_head resource_list;
+	struct i2c_adapter_lookup lookup;
+	struct i2c_msg msg;
+	int ret;
+	u8 vbt_i2c_bus_num = *(data + 2);
+	u16 slave_addr = *(u16 *)(data + 3);
+	u8 reg_offset = *(data + 5);
+	u8 payload_size = *(data + 6);
+	u8 *payload_data;
+
+	if (intel_dsi->i2c_bus_num < 0) {
+		intel_dsi->i2c_bus_num = vbt_i2c_bus_num;
+
+		acpi_dev = ACPI_COMPANION(dev);
+		if (acpi_dev) {
+			memset(&lookup, 0, sizeof(lookup));
+			lookup.slave_addr = slave_addr;
+			lookup.intel_dsi = intel_dsi;
+			lookup.dev_handle = acpi_device_handle(acpi_dev);
+
+			INIT_LIST_HEAD(&resource_list);
+			acpi_dev_get_resources(acpi_dev, &resource_list,
+					       i2c_adapter_lookup,
+					       &lookup);
+			acpi_dev_free_resource_list(&resource_list);
+		}
+	}
 
-	return data + *(data + 6) + 7;
+	adapter = i2c_get_adapter(intel_dsi->i2c_bus_num);
+	if (!adapter) {
+		DRM_DEV_ERROR(dev, "Cannot find a valid i2c bus for xfer\n");
+		goto err_bus;
+	}
+
+	payload_data = kzalloc(payload_size + 1, GFP_KERNEL);
+	if (!payload_data)
+		goto err_alloc;
+
+	payload_data[0] = reg_offset;
+	memcpy(&payload_data[1], (data + 7), payload_size);
+
+	msg.addr = slave_addr;
+	msg.flags = 0;
+	msg.len = payload_size + 1;
+	msg.buf = payload_data;
+
+	ret = i2c_transfer(adapter, &msg, 1);
+	if (ret < 0)
+		DRM_DEV_ERROR(dev,
+			      "Failed to xfer payload of size (%u) to reg (%u)\n",
+			      payload_size, reg_offset);
+
+	kfree(payload_data);
+err_alloc:
+	i2c_put_adapter(adapter);
+err_bus:
+	return data + payload_size + 7;
 }
 
 static const u8 *mipi_exec_spi(struct intel_dsi *intel_dsi, const u8 *data)
@@ -683,6 +776,8 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
 	intel_dsi->panel_off_delay = pps->panel_off_delay / 10;
 	intel_dsi->panel_pwr_cycle_delay = pps->panel_power_cycle_delay / 10;
 
+	intel_dsi->i2c_bus_num = -1;
+
 	/* a regular driver would get the device in probe */
 	for_each_dsi_port(port, intel_dsi->ports) {
 		mipi_dsi_attach(intel_dsi->dsi_hosts[port]->device);