[v4,0/2] ALSA: Add driver for big Scarlett 4th Gen interfaces

Message

Geoffrey D. Bennett Jan. 4, 2025, 5:11 p.m. UTC

Hi Takashi,

Thanks again for your feedback. Requested changes made.

> Now, considering this implementation again, a fundamental question is
> whether we really should go to this direction or not.
> 
> Usually the driver implements an ioctl per certain limited task
> (except for some debugging purpose).  But we open all doors fully.
> This gives the most flexibility, of course.  OTOH, it has a
> significant risk that every program may screw up your device easily by
> sending some malicious ioctls.

That is a good point. To eliminate that risk and prevent malicious use
entirely, I added a requirement in v4 of having CAP_SYS_RAWIO to use
the hwdep interface. In addition, I have added validation of the flash
commands to prevent the App_Gold flash segment from being accidentally
erased or written to (this segment contains the backup firmware used
when the App_Upgrade segment does not contain a valid firmware image).
I think this way we can have both flexibility and safety.

Regards,
Geoffrey.

---
Changes in v4:
- Use variable-length data arrays in ioctl structs instead of pointers
- Add CAP_SYS_RAWIO requirement to hwdep interface
- Add validation of flash commands to prevent accidental bricking due
  to erasing/writing the App_Gold segment
- Refactor URB cleanup

---
Changes in v3:
- Update ioctl structs and add ioctl_compat op to work with 32-bit
  userspace on 64-bit kernels
- Update driver to do all init steps so it can re-init after
  suspend/resume
- Add version field to init ioctl for future compatibility
- Improve error messages when unexpected response data is received

---
Changes in v2 as per Takashi's feedback:
- Use fixed-size data arrays instead of pointers in ioctl structs
- Define notify struct outside of struct fcp_dev
- Use u8/u16 types without __ prefix
- Use cleanup.h for code simplification
- Add init flag to ensure FCP_IOCTL_INIT is called before
  FCP_IOCTL_CMD and FCP_IOCTL_SET_METER_MAP
- Do not destroy/recreate the meter control (the number of channels is
  now fixed when it is created)

Geoffrey D. Bennett (2):
  ALSA: FCP: Add Focusrite Control Protocol driver
  ALSA: scarlett2: Add device_setup option to use FCP driver

 MAINTAINERS                 |   10 +-
 include/uapi/sound/fcp.h    |   71 +++
 sound/usb/Makefile          |    1 +
 sound/usb/fcp.c             | 1018 +++++++++++++++++++++++++++++++++++
 sound/usb/fcp.h             |    7 +
 sound/usb/mixer_quirks.c    |    7 +
 sound/usb/mixer_scarlett2.c |    8 +
 7 files changed, 1118 insertions(+), 4 deletions(-)
 create mode 100644 include/uapi/sound/fcp.h
 create mode 100644 sound/usb/fcp.c
 create mode 100644 sound/usb/fcp.h