Re: [PATCH v2 2/2] mfd: Add initial synology microp driver

[Greg Kroah-Hartman]

On Mon, Mar 09, 2026 at 12:52:26PM +0000, Markus Probst wrote:
> On Mon, 2026-03-09 at 06:56 +0100, Greg Kroah-Hartman wrote:
> > On Sun, Mar 08, 2026 at 07:15:16PM +0000, Markus Probst wrote:
> > > On Sun, 2026-03-08 at 19:55 +0100, Greg Kroah-Hartman wrote:
> > > > On Sun, Mar 08, 2026 at 06:41:20PM +0000, Markus Probst wrote:
> > > > > Add a initial synology microp driver, written in Rust.
> > > > > The driver targets a microcontroller found in Synology NAS devices. It
> > > > > currently only supports controlling of the power led, status led, alert
> > > > > led and usb led. Other components such as fan control or handling
> > > > > on-device buttons will be added once the required rust abstractions are
> > > > > there.
> > > > 
> > > > Why is this a mfd device?  Shouldn't it be an aux device?
> > > > 
> > > > But this is just a serial port connection, so why is a kernel driver
> > > > needed at all?
> > > I am not sure what you mean.
> > 
> > Can't this just be controlled from userspace over the tty device to the
> > uart this device uses?  Why is a kernel driver needed at all?
> Like with any other bus device, it can be controlled by userspace.

Great, then usually that means it should not be a kernel driver :)

> But the kernel already provides the necessary userspace interfaces for
> leds, hwmon, input etc. for any userspace application to access.

True, but:

> Furthermore it is required for proper shutdown and reboot, which is a
> kernel task.

What do you mean by this?  What does it do for shutdown and reboot?

Is there an out-of-tree C kernel driver for this somewhere?  Or does it
all just work through userspace today on these devices?

> On arm devices, it completely takes care of the poweroff and reboot.
> There is already a driver here drivers/power/reset/qnap-poweroff.c,
> which seems to be primarily developed for QNAP, but works for Synology
> too.

But that's not this device, that's a different device and driver.

> On x86 devices, is uses ACPI Sleep, but must still announce the
> poweroff / reboot prior to the firmware call to the device for proper
> shutdown / reboot. There is no existing driver that takes care of this
> yet.

Then that should be a kernel driver, no need for the led blinks to be a
kernel driver if they don't have to, right?  We try to only put stuff in
the kernel that _has_ to be in the kernel, within reason.

thanks,

greg k-h