Hi, Len On some boxes there is neither generic ACPI backlight I/F nor platform backlight I/F. That means that the backlight brightness can't be changed by using sys backlight I/F. But the backlight brightness can be changed by using the driver backlight I/F. For example: on the box based on intel-integrated graphics card the backlight brightness can also be changed by using the LBB register in pci device. Can the graphics driver register the sys backlight I/F so that we can change the backlight by using sys I/F? If the graphics driver can also register the backlight I/F, it seems that we can register three types of backlight I/F. a. generic ACPI backlight I/F. This is registered by acpi video driver. b. platform backlight I/F. This is registered by the platform driver c. graphics backlight I/F. This can be registered by the graphics driver. As there exist three types of backlight I/F, how can we make the coordination among the three backlight I/F? In fact only one backlight I/f is enough for user to change the brightness. Rui provides a propose that use the backlight manager to choose the appropriate the backlight I/F. backlight manager only exports one single I/F to users, like: ----| |----brightness |----actual_brightness |----max_brightness |----... |----mode and it supports multiple modes, e.g. 1. generic ---ACPI 2. platform---platform drivers 3. legacy-----i915 The sysfs backlight manager always chooses the mode with highest priority (generic > platform > legacy), and call the respective callbacks when backlight is changed. For example, the backlight manager switches to the "generic" mode from "legacy" mode automatically when ACPI video driver is loaded at runtime. How about the above propose? BTW: now in the video driver only one of acpi generic backlight I/F and platform backlight I/F is registered. That means that the acpi generic backlight I/F is preferred if it exists. Of course we can switch to the platform backlight I/F by adding the boot option of "acpi_backlight=vendor". In summary, the platform driver will check whether the acpi generic backlight is supported before registering the platform backlight I/F. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html