that the ioctl() API is synchronous is fine to me, however pushing thatSorry for this taking too long (vacations, conferences, you name it) fornot necessarily from user space, but at least from HID core to HIDP andI'm open to suggestions. The way I see it is from a user spacethere is not and I don't think we ever get one. My question here waswhat is usb-hid.ko doing here? I would expect a bunch of codeusbhid doesn't have a lot of code for hidraw. Two functions are involved:
duplication with minor difference between USB and Bluetooth.
usbhid_output_raw_report()
- calls usb_control_msg() with Get_Report
usbhid_get_raw_report()
- calls usb_control_msg() with Set_Report
OR
- calls usb_interrupt_msg() on the Ouput pipe.
This is of course easier than bluetooth because usb_control_msg() is
synchronous, even when requesting reports, mostly because of the nature
of USB, where the request and response are part of the same transfer.
For Bluetooth, it's a bit more complicated since the kernel treats it
more like a networking interface (and indeed it is). My understanding is
that to make a synchronous transfer in bluetooth, one must:
- send the request packet
- block (wait_event_*())
- when the response is received in the input handler, wake_up_*().
There's not really any code duplication, mostly because initiating
synchronous USB transfers (input and output) is easy (because of the
usb_*_msg() functions), while making synchronous Bluetooth transfers
must be done manually. If there's a nice, convenient, synchronous
function in Bluetooth similar to usb_control_msg() that I've missed,
then let me know, as it would simplify this whole thing.
more in the direction why HID core is doing these synchronously in the
first place. Especially since USB can do everything async as well.
perspective. With Get_Feature being on an ioctl(), I don't see any clean
way to do it other than synchronously. Other operating systems (I can
say for sure Windows, Mac OS X, and FreeBSD) handle Get/Set Feature the
same way (synchronously) from user space.
You seem to be proposing an asynchronous interface. What would that look
like from user space?
usb-hid transports. At least that is what I would expect, Jiri?
me to respond.
As all the _raw() callbacks are purely intended for userspace interaction
anyway, it's perfectly fine (and in fact desirable) for the low-level
transport drivers to perform these operations synchronously (and that's
what USB implementation does as well).
Marcel, if your opposition to synchronous interface is strong, we'll have
to think about other aproaches, but from my POV, the patch is fine as-is
for Bluetooth.
down to the transport drivers seems wrong to me. I think the HID core
should be able to handle a fully asynchronous transport driver. I know
that with the USB subsystem you are little bit spoiled here, but for
Bluetooth it is not the case. And in the end even using the asynchronous
USB URB calls would be nice as well.
So why not make the core actually wait for responses from the transport
driver.
I would make the transport drivers a lot simpler in the long
run.
And I know that most likely besides Bluetooth and USB you won't see
another, but you never know.