On Mon, Oct 16, 2023 at 03:28:11PM +0200, Jaroslav Kysela wrote: > On 16. 10. 23 14:32, Geoffrey D. Bennett wrote: > > 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). > > Thank you for this bigger picture. But except the firmware upgrade, all > those functions seem to be implementable in a more abstract way using > standard control API. Note that we can assign the controls also to card > (e.g. SNDRV_CTL_ELEM_IFACE_CARD) to classify them as non-mixer. Hi Jaroslav, By "more abstract way", you mean to have a control for every parameter which could be read or written? I can see that working for things like firmware version, device name, and channel name, but I think it would be pretty awful for the software configuration space that Focusrite Control uses, and bloat the driver quite a bit for what seems to me to be something more suited to user-land implementation. (an aside, will alsactl store/restore SNDRV_CTL_ELEM_TYPE_BYTES?) Or am I misunderstanding and you mean there is already a way (like SNDRV_CTL_IOCTL_TLV_COMMAND?) to send commands & get responses? By "pretty awful"/bloat, a bit more explanation: (1) Part of the NVRAM that can be accessed refers to the hardware controls which the driver allows the user to read/write (such as dim/mute/volume/level/pad/air/phantom/etc.) (2) Part of the NVRAM is used by the Focusrite Control software to store the state of the interface in a higher-level way. It does not support all features of the hardware (e.g. routing is quite restricted). It's not possible to represent all functions of (1) inside (2), so when I developed the driver I ignored (2) and implemented all features of (1). It doesn't make sense to implement (2) in the kernel as that would double the number of controls, but what would make sense would be a user-space application that implements read/write of (2) with a UI that restricts the user to what can be represented in (2). For example: in (1), routing is all mono vs. in (2) routing is stereo-only, channels can be paired together, and there are balance/pan controls. I feel strongly this is the sort of thing where the kernel provides the low-level (1) hardware interface, and a user-space app provides a higher-level (2) interface. It'd be nice if the app could store this data on the device itself like Focusrite Control does. And perhaps it could even do this in a non-Focusrite Control compatible way (for additional functionality when compatibility is not desired). But those options are not feasible if there is no access to read/write NVRAM arbitrarily. That's why I came up with the proposed ioctl interface to the scarlett2_usb() function. That will allow user-space to access all applicable functions: - reboot - get flash info - get flash segment info - erase flash segment - get erase segment progress - write flash segment - read NVRAM - write NVRAM through a common interface, without disconnecting the kernel driver, and without adding specific support for a bunch of things that are not applicable to the hardware controls (1). Thanks, Geoffrey.
