On Mar 13 2025, Rahul Rameshbabu wrote: > This code will eventually contain the logic needed to drive the backlight > of displays that implement the USB Monitor Control Class specification. > Examples include the Apple Studio Display and Apple Pro Display XDR > monitors. USB Monitor Control Class encompasses more than just backlight > control, so the driver could be further extended as monitors support more > functionality in the specification. > > This code is a skeleton currently, where the focus right now is on the core > Rust API. The driver skeleton was written before approaching the Rust API > and C binding work. This was done to provide a guide for what the Rust API > should look like and avoid any rough C binding work from being exposed to > Rust HID device drivers. skeletons are good for documentation, but not really for code review as they can not compile. You should make this patch part of a documentation in Documentation/hid/, and squash it with the next one (having a minimal full driver instead of skeleton+fill in the voids). Cheers, Benjamin > > To go forward with this driver for the purpose of external monitor > backlight control, a new DRM backlight API that is scoped per connector > will be required. I am currently in the process of developing this new API. > I document the details in my related blog posts. The issue with the current > backlight API is it was designed on the assumption that only internal > panels have controllable backlights. Using this assumption combined with > another that there can only ever be a single internal panel, having more > than one device register with the backlight interface would confuse > userspace applications. > > Julius Zint originally tried to implement such a driver a bit more than a > year ago with a C driver but was blocked by the limitations of the > backlight API. I asked him for permission to continue the work in Rust > while accrediting him for the HID report parsing logic for the backlight > support in the USB Monitor Control Class specification. > > Cc: Julius Zint <julius@xxxxxxx> > Link: https://lore.kernel.org/lkml/20230820094118.20521-1-julius@xxxxxxx/ > Link: https://binary-eater.github.io/posts/linux_usb_monitor_control/ > Link: https://www.usb.org/sites/default/files/usbmon11.pdf > Signed-off-by: Rahul Rameshbabu <sergeantsagara@xxxxxxxxxxxxxx> > --- > drivers/hid/Kconfig | 8 +++++++ > drivers/hid/Makefile | 1 + > drivers/hid/hid_monitor_control.rs | 37 ++++++++++++++++++++++++++++++ > 3 files changed, 46 insertions(+) > create mode 100644 drivers/hid/hid_monitor_control.rs > > diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig > index e085964c7ffc..92be13acb956 100644 > --- a/drivers/hid/Kconfig > +++ b/drivers/hid/Kconfig > @@ -722,6 +722,14 @@ config RUST_HID_ABSTRACTIONS > Adds support needed for HID drivers written in Rust. It provides a > wrapper around the C hid core. > > +config HID_MONITOR_CONTROL > + tristate "USB Monitor Control Class support" > + depends on USB_HID > + depends on RUST_HID_ABSTRACTIONS > + help > + Say Y here if you want to enable control over a monitor that uses USB > + Monitor Control Class. > + > config HID_REDRAGON > tristate "Redragon keyboards" > default !EXPERT > diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile > index 482b096eea28..bf8b096bcf23 100644 > --- a/drivers/hid/Makefile > +++ b/drivers/hid/Makefile > @@ -86,6 +86,7 @@ obj-$(CONFIG_HID_MCP2221) += hid-mcp2221.o > obj-$(CONFIG_HID_MAYFLASH) += hid-mf.o > obj-$(CONFIG_HID_MEGAWORLD_FF) += hid-megaworld.o > obj-$(CONFIG_HID_MICROSOFT) += hid-microsoft.o > +obj-$(CONFIG_HID_MONITOR_CONTROL) += hid_monitor_control.o > obj-$(CONFIG_HID_MONTEREY) += hid-monterey.o > obj-$(CONFIG_HID_MULTITOUCH) += hid-multitouch.o > obj-$(CONFIG_HID_NINTENDO) += hid-nintendo.o > diff --git a/drivers/hid/hid_monitor_control.rs b/drivers/hid/hid_monitor_control.rs > new file mode 100644 > index 000000000000..18afd69a56d5 > --- /dev/null > +++ b/drivers/hid/hid_monitor_control.rs > @@ -0,0 +1,37 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +// Copyright (C) 2025 Rahul Rameshbabu <sergeantsagara@xxxxxxxxxxxxxx> > + > +use kernel::prelude::*; > +use kernel::hid::{ > + self, > + Driver, > +}; > + > +struct HidMonitorControl; > + > +#[vtable] > +impl Driver for HidMonitorControl { > + fn probe(dev: &mut hid::Device, id: &hid::DeviceId) -> Result<()> { > + /* TODO implement */ > + Ok(()) > + } > + > + fn remove(dev: &mut hid::Device) { > + /* TODO implement */ > + } > +} > + > +kernel::module_hid_driver! { > + driver: HidMonitorControl, > + id_table: [ > + kernel::usb_device! { > + vendor: /* TODO fill in */, > + product: /* TODO fill in */, > + }, > + ], > + name: "monitor_control", > + author: "Rahul Rameshbabu <sergeantsagara@xxxxxxxxxxxxxx>", > + description: "Driver for the USB Monitor Control Class", > + license: "GPL", > +} > -- > 2.47.2 > >
