On 07/09/2010 09:06 AM, Marcel Holtmann wrote:
I looked at this and I am bit worried that this should not be done in
this detail in the HIDP driver. Essentially HIDP is a pure transport
driver. It should not handle all these details. Can we make this a bit
easier for the transport drivers to support such features?
I put these changes (most notably the addition of hidp_get_raw_report())
in hidp because that's where the parallel function
hidp_output_raw_report() was already located. I figured the input should
go with the output. That said, if there's a better place for both of
them (input and output) to go, let me know where you think it should be,
and I'll get them moved into the proper spot.
I'm not sure what you mean about HIDP being a pure transport driver.
what is usb-hid.ko doing here? I would expect a bunch of code
duplication with minor difference between USB and Bluetooth.
usbhid doesn't have a lot of code for hidraw. Two functions are involved:
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.
there is not and I don't think we ever get one. My question here was
more in the direction why HID core is doing these synchronously in the
first place. Especially since USB can do everything async as well.
Regards
Marcel
Hi Marcel,
I'm open to suggestions. The way I see it is from a user space
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?
Alan.
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