Re: [PATCH RFC] ALSA: scarlett2: Add ioctls for user-space access

["Geoffrey D. Bennett" <g@b4.vu>]

On Mon, Oct 16, 2023 at 09:04:21AM +0200, Jaroslav Kysela wrote:
> On 14. 10. 23 15:58, Geoffrey D. Bennett wrote:
> > In order to support functions such as firmware upgrade from
> > user-space, add ioctls for submitting arbitrary proprietary requests
> > through scarlett2_usb() and requesting/releasing exclusive access.
> > ---
> > 
> > Hi Takashi,
> > 
> > I recently figured how to update the firmware on Scarlett Gen 2+
> > devices. I think the best way to implement this is with an ioctl
> > giving access to the scarlett2_usb() function from user-space, plus
> > two ioctls to request/release exclusive access.
> > 
> > Does something like this seem reasonable?
> 
> Maybe you can use libusb for this job without an additional kernel
> interface. It allows to detach the USB kernel driver and attach it again
> when the job is complete.

Hi Jaroslav,

I considered using libusb (I used it during initial development of the
driver), and if the only purpose of the ioctl would be for firmware
updates then it would be reasonable to detach the kernel driver for
that. However...

Beyond just being able to do firmware operations, that ioctl would
also allow access to all of the configuration space using cmd =
SCARLETT2_USB_GET_DATA and SCARLETT2_USB_SET_DATA. I think this would
be the cleanest way to allow implementing non-mixer related
functionality in user-space, such as reading the current firmware
version, reading/updating the device name and channel names, and
updating the software configuration space for Focusrite Control
compatibility to name a few. These sorts of applications need to be
able to make these proprietary requests through the scarlett2 driver
to avoid disrupting it (or disrupting audio).

Regards,
Geoffrey.