The Apple Studio Display does not have any physical buttons and the only
way to get or set the brightness is by sending USB control transfers to a
HID device exposed by the display.
These control transfers take the form of a HID_(GET|SET)_REPORT request
and the payload looks like this:
struct brightness_ctrl_message_data {
u8 unknown_1;
__le16 brightness;
u8 unkown_2[4];
} __packed;
When compiled as a module this driver needs to be part of the early boot
environment, otherwise the generic USB HID driver will claim the device.
Signed-off-by: Julius Zint <julius@xxxxxxx>
---
drivers/video/backlight/Kconfig | 8 +
drivers/video/backlight/Makefile | 1 +
drivers/video/backlight/apple_bl_usb.c | 264 +++++++++++++++++++++++++
3 files changed, 273 insertions(+)
create mode 100644 drivers/video/backlight/apple_bl_usb.c
diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index 51387b1ef012..9383d402ebed 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -290,6 +290,14 @@ config BACKLIGHT_APPLE
If you have an Intel-based Apple say Y to enable a driver for its
backlight.
+config BACKLIGHT_APPLE_USB
+ tristate "Apple USB Backlight Driver"
+ depends on USB
+ help
+ If you have an external display from Apple that is attached via USB
+ say Y to enable a driver for its backlight. Currently it supports the
+ Apple Studio Display.
+
config BACKLIGHT_QCOM_WLED
tristate "Qualcomm PMIC WLED Driver"
select REGMAP
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index f72e1c3c59e9..c42880655113 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -23,6 +23,7 @@ obj-$(CONFIG_BACKLIGHT_ADP5520) += adp5520_bl.o
obj-$(CONFIG_BACKLIGHT_ADP8860) += adp8860_bl.o
obj-$(CONFIG_BACKLIGHT_ADP8870) += adp8870_bl.o
obj-$(CONFIG_BACKLIGHT_APPLE) += apple_bl.o
+obj-$(CONFIG_BACKLIGHT_APPLE_USB) += apple_bl_usb.o
obj-$(CONFIG_BACKLIGHT_AS3711) += as3711_bl.o
obj-$(CONFIG_BACKLIGHT_BD6107) += bd6107.o
obj-$(CONFIG_BACKLIGHT_CARILLO_RANCH) += cr_bllcd.o
diff --git a/drivers/video/backlight/apple_bl_usb.c b/drivers/video/backlight/apple_bl_usb.c
new file mode 100644
index 000000000000..b746b7822974
--- /dev/null
+++ b/drivers/video/backlight/apple_bl_usb.c
@@ -0,0 +1,264 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/backlight.h>
+#include <asm/byteorder.h>
+
+#define APPLE_STUDIO_DISPLAY_VENDOR_ID 0x05ac
+#define APPLE_STUDIO_DISPLAY_PRODUCT_ID 0x1114
+
+#define HID_GET_REPORT 0x01
+#define HID_SET_REPORT 0x09
+
+#define HID_REPORT_TYPE_FEATURE 0x0300
+
+struct apple_bl_usb_data {
+ struct usb_interface *usb_interface;
+ struct usb_device *usb_dev;
+};
+
+struct brightness_ctrl_message_data {
+ u8 unknown_1;
+ __le16 brightness;
+ u8 unkown_2[4];
+} __packed;
+
+void init_ctrl_msg_data(struct brightness_ctrl_message_data *msg)
+{
+ memset(msg, 0, sizeof(struct brightness_ctrl_message_data));
+ msg->unknown_1 = 0x01;
+}
+
+void set_ctrl_message_brightness(struct brightness_ctrl_message_data *msg,
+ u16 brightness_value)
+{
+ msg->brightness = cpu_to_le16(brightness_value + 400);
+}
+
+u16 get_ctrl_message_brightness(struct brightness_ctrl_message_data *msg)
+{
+ return le16_to_cpu(msg->brightness) - 400;
+}
+
+int apple_bl_usb_usb_get_brightness(struct usb_interface *interface,
+ struct usb_device *usb_dev,
+ int *brightness)
+{
+ int err;
+ u16 interface_nr;
+ int msg_data_size;
+ struct brightness_ctrl_message_data *msg_data;
+
+ msg_data_size = sizeof(struct brightness_ctrl_message_data);
+ msg_data = kzalloc(msg_data_size, GFP_KERNEL);
+ memset(msg_data, 0x00, msg_data_size);
+ interface_nr = interface->cur_altsetting->desc.bInterfaceNumber;
+
+ err = usb_control_msg(usb_dev,
+ usb_rcvctrlpipe(usb_dev, 0),
+ HID_GET_REPORT,
+ USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+ /* wValue: HID-Report Type and Report ID */
+ HID_REPORT_TYPE_FEATURE | 0x01,
+ interface_nr /* wIndex */,
+ msg_data,
+ msg_data_size,
+ HZ);
+ if (err < 0) {
+ dev_err(&interface->dev,
+ "get: usb control message err: %d\n",
+ err);
+ }
+ *brightness = get_ctrl_message_brightness(msg_data);
+ kfree(msg_data);
+ dev_dbg(&interface->dev, "get brightness: %d\n", *brightness);
+ return 0;
+}
+
+int apple_bl_usb_usb_set_brightness(struct usb_interface *interface,
+ struct usb_device *usb_dev,
+ int brightness)
+{
+ int err;
+ u16 interface_nr;
+ struct brightness_ctrl_message_data *msg_data;
+
+ msg_data = kzalloc(sizeof(struct brightness_ctrl_message_data), GFP_KERNEL);
+ interface_nr = interface->cur_altsetting->desc.bInterfaceNumber;
+ init_ctrl_msg_data(msg_data);
+ set_ctrl_message_brightness(msg_data, brightness);
+
+ err = usb_control_msg(usb_dev,
+ usb_sndctrlpipe(usb_dev, 0),
+ HID_SET_REPORT,
+ USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+ /* wValue: HID-Report Type and Report ID */
+ HID_REPORT_TYPE_FEATURE | 0x01,
+ interface_nr /* wIndex */,
+ msg_data,
+ sizeof(struct brightness_ctrl_message_data),
+ HZ);
+ kfree(msg_data);
+ if (err < 0) {
+ dev_err(&interface->dev,
+ "set: usb control message err: %d\n",
+ err);
+ return err;
+ }
+ dev_dbg(&interface->dev, "set brightness: %d\n", brightness);
+ return 0;
+}
+
+int apple_bl_usb_check_fb(struct backlight_device *bd, struct fb_info *info)
+{
+ dev_info(&bd->dev, "check fb\n");
+ return 0;
+}
+
+int apple_bl_usb_get_brightness(struct backlight_device *bl)
+{
+ int ret;
+ struct apple_bl_usb_data *data;
+ int hw_brightness;
+
+ data = bl_get_data(bl);
+ ret = apple_bl_usb_usb_get_brightness(data->usb_interface,
+ data->usb_dev,
+ &hw_brightness);
+ if (!ret)
+ ret = hw_brightness;
+
+ return ret;
+}
+
+int apple_bl_usb_update_status(struct backlight_device *bl)
+{
+ int err;
+ struct apple_bl_usb_data *data;
+
+ data = bl_get_data(bl);
+ err = apple_bl_usb_usb_set_brightness(data->usb_interface,
+ data->usb_dev,
+ bl->props.brightness);
+ return err;
+}
+
+static const struct backlight_ops apple_bl_usb_ops = {
+ .update_status = apple_bl_usb_update_status,
+ .get_brightness = apple_bl_usb_get_brightness,
+ .check_fb = apple_bl_usb_check_fb,
+};
+
+static void apple_bl_usb_disconnect(struct usb_interface *interface)
+{
+ struct backlight_device *bl;
+
+ dev_dbg(&interface->dev, "disconnect\n");
+
+ bl = usb_get_intfdata(interface);
+ usb_set_intfdata(interface, NULL);
+ backlight_device_unregister(bl);
+}
+
+static int apple_bl_usb_probe(struct usb_interface *interface,
+ const struct usb_device_id *id)
+{
+ struct backlight_properties props;
+ struct backlight_device *bl;
+ struct usb_device *usb_dev;
+ struct device *dev;
+ struct apple_bl_usb_data *data;
+ int brightness_interface_nr;
+
+ dev_dbg(&interface->dev, "probe\n");
+
+ dev = &interface->dev;
+ usb_dev = interface_to_usbdev(interface);
+
+ switch (usb_dev->config->desc.bConfigurationValue) {
+ case 1:
+ brightness_interface_nr = 0x7;
+ break;
+ case 2:
+ brightness_interface_nr = 0x9;
+ break;
+ case 3:
+ brightness_interface_nr = 0xc;
+ break;
+ default:
+ dev_err(dev,
+ "unexpected configuration value: %d\n",
+ usb_dev->config->desc.bConfigurationValue);
+ return -EINVAL;
+ }
+
+ if (interface->cur_altsetting->desc.bInterfaceNumber != brightness_interface_nr)
+ return -ENODEV;
+
+ data = devm_kzalloc(dev,
+ sizeof(struct apple_bl_usb_data),
+ GFP_KERNEL);
+ if (IS_ERR(data)) {
+ dev_err(dev, "failed to allocate memory\n");
+ return PTR_ERR(bl);
+ }
+ data->usb_interface = interface;
+ data->usb_dev = usb_dev;
+
+ // Valid brightness values for the apple studio display range from 400
+ // to 60000. Since the backlight subsystem´s brightness value starts
+ // from 0, we use 0 to 59600 and offset it by the minimum value.
+ memset(&props, 0, sizeof(props));
+ props.type = BACKLIGHT_RAW;
+ props.max_brightness = 59600;
+
+ bl = backlight_device_register("apple_studio_display",
+ dev,
+ data,
+ &apple_bl_usb_ops,
+ &props);
+ if (IS_ERR(bl)) {
+ dev_err(dev, "failed to register backlight\n");
+ return PTR_ERR(bl);
+ }
+ usb_set_intfdata(interface, bl);
+ return 0;
+}
+
+static int apple_bl_usb_suspend(struct usb_interface *interface,
+ pm_message_t message)
+{
+ dev_dbg(&interface->dev, "suspend\n");
+ return 0;
+}
+
+static int apple_bl_usb_resume(struct usb_interface *interface)
+{
+ dev_dbg(&interface->dev, "resume\n");
+ return 0;
+}
+
+static const struct usb_device_id id_table[] = {
+ {
+ .idVendor = APPLE_STUDIO_DISPLAY_VENDOR_ID,
+ .idProduct = APPLE_STUDIO_DISPLAY_PRODUCT_ID,
+ },
+ {},
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+static struct usb_driver usb_asdbl_driver = {
+ .name = "apple_bl_usb",
+ .probe = apple_bl_usb_probe,
+ .disconnect = apple_bl_usb_disconnect,
+ .id_table = id_table,
+ .suspend = apple_bl_usb_suspend,
+ .resume = apple_bl_usb_resume,
+ .reset_resume = apple_bl_usb_resume
+};
+module_usb_driver(usb_asdbl_driver);
+
+MODULE_AUTHOR("Julius Zint <julius@xxxxxxx>");
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_DESCRIPTION("Backlight control for USB-C Thunderbolt Apple displays");
--
2.41.0
