Hi everyone,
I'm working on a firmware of a device that exposes a HID interface via
USB and/or BLE and uses, among other things, non-numbered feature
reports. Included in this series are two paches I had to create in
order for hidraw devices created for aforementioned subsystems to
behave in the same way when exerciesd by the same test tool.
I don't know if the patches are acceptable as-is WRT to not breaking
existing userspace, hence the RFC tag.
Andrey Smirnov (2):
HID: uhid: Don't send the report ID if it's zero
HID: usbhid: Don't include report ID zero into returned data
drivers/hid/uhid.c | 15 ++++++++++++---
drivers/hid/usbhid/hid-core.c | 14 --------------
2 files changed, 12 insertions(+), 17 deletions(-)
--
2.34.1
Report ID of zero is a special case for ID-less reports, which by
definition do not have report ID as a part of their payload. Not
returning an extra zero also matches hidraw documentation,
specifically:
For devices which do not use numbered reports, set the first
byte to 0. The returned report buffer will contain the report
number in the first byte, followed by the report data read from
the device. For devices which do not use numbered reports, the
report data will begin at the first byte of the returned buffer.
Cc: David Rheinsberg <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Benjamin Tissoires <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Andrey Smirnov <[email protected]>
---
drivers/hid/usbhid/hid-core.c | 14 --------------
1 file changed, 14 deletions(-)
diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index be4c731aaa65..575f09003602 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -874,18 +874,8 @@ static int usbhid_get_raw_report(struct hid_device *hid,
struct usb_device *dev = hid_to_usb_dev(hid);
struct usb_interface *intf = usbhid->intf;
struct usb_host_interface *interface = intf->cur_altsetting;
- int skipped_report_id = 0;
int ret;
- /* Byte 0 is the report number. Report data starts at byte 1.*/
- buf[0] = report_number;
- if (report_number == 0x0) {
- /* Offset the return buffer by 1, so that the report ID
- will remain in byte 0. */
- buf++;
- count--;
- skipped_report_id = 1;
- }
ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
HID_REQ_GET_REPORT,
USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
@@ -893,10 +883,6 @@ static int usbhid_get_raw_report(struct hid_device *hid,
interface->desc.bInterfaceNumber, buf, count,
USB_CTRL_SET_TIMEOUT);
- /* count also the report id */
- if (ret > 0 && skipped_report_id)
- ret++;
-
return ret;
}
--
2.34.1
Hi
On Mon, 5 Dec 2022 at 22:04, Andrey Smirnov <[email protected]> wrote:
> I'm working on a firmware of a device that exposes a HID interface via
> USB and/or BLE and uses, among other things, non-numbered feature
> reports. Included in this series are two paches I had to create in
> order for hidraw devices created for aforementioned subsystems to
> behave in the same way when exerciesd by the same test tool.
>
> I don't know if the patches are acceptable as-is WRT to not breaking
> existing userspace, hence the RFC tag.
Can you elaborate why you remove the special handling from USBHID but
add it to UHID? They both operate logically on the same level, so
shouldn't we simply adjust uhid to include the report-id in buf[0]?
Also, you override buf[0] in UHID, so I wonder what UHID currently
returns there?
IOW, can you elaborate a bit what the current behavior of each of the
involved modules is, and what behavior you would expect? This would
allow to better understand what you are trying to achieve. The more
context you can give, the easier it is to understand what happens
there.
Thanks!
David
On Thu, Dec 8, 2022 at 7:46 AM David Rheinsberg
<[email protected]> wrote:
>
> Hi
>
> On Mon, 5 Dec 2022 at 22:04, Andrey Smirnov <[email protected]> wrote:
> > I'm working on a firmware of a device that exposes a HID interface via
> > USB and/or BLE and uses, among other things, non-numbered feature
> > reports. Included in this series are two paches I had to create in
> > order for hidraw devices created for aforementioned subsystems to
> > behave in the same way when exerciesd by the same test tool.
> >
> > I don't know if the patches are acceptable as-is WRT to not breaking
> > existing userspace, hence the RFC tag.
>
> Can you elaborate why you remove the special handling from USBHID but
> add it to UHID? They both operate logically on the same level, so
> shouldn't we simply adjust uhid to include the report-id in buf[0]?
>
> Also, you override buf[0] in UHID, so I wonder what UHID currently
> returns there?
>
> IOW, can you elaborate a bit what the current behavior of each of the
> involved modules is, and what behavior you would expect? This would
> allow to better understand what you are trying to achieve. The more
> context you can give, the easier it is to understand what happens
> there.
>
Sorry it's not very clear, so the difference between the cases is that
in the case of UHID the report ID ends up being included as a part of
"SET_FEATURE", so BlueZ checks UHID_DEV_NUMBERED_FEATURE_REPORTS,
which is not set (correctly) and tries to send the whole payload. This
ends up as a maxlen + 1 (extra byte) write to a property that is
maxlen long, which gets rejected by device's BLE stack.
In the case of USBHID the problem happens in "GET_FEATURE" path. When
userspace reads the expected data back it gets an extra 0 prepended to
the payload, so all of the actual payload has an offset of 1. This
doesn't happen with UHID, which I think is the correct behavior here.
Hopefully that explains the difference, let me know if something is unclear
Hi
On Thu, 8 Dec 2022 at 21:59, Andrey Smirnov <[email protected]> wrote:
>
> On Thu, Dec 8, 2022 at 7:46 AM David Rheinsberg
> <[email protected]> wrote:
> >
> > Hi
> >
> > On Mon, 5 Dec 2022 at 22:04, Andrey Smirnov <[email protected]> wrote:
> > > I'm working on a firmware of a device that exposes a HID interface via
> > > USB and/or BLE and uses, among other things, non-numbered feature
> > > reports. Included in this series are two paches I had to create in
> > > order for hidraw devices created for aforementioned subsystems to
> > > behave in the same way when exerciesd by the same test tool.
> > >
> > > I don't know if the patches are acceptable as-is WRT to not breaking
> > > existing userspace, hence the RFC tag.
> >
> > Can you elaborate why you remove the special handling from USBHID but
> > add it to UHID? They both operate logically on the same level, so
> > shouldn't we simply adjust uhid to include the report-id in buf[0]?
> >
> > Also, you override buf[0] in UHID, so I wonder what UHID currently
> > returns there?
> >
> > IOW, can you elaborate a bit what the current behavior of each of the
> > involved modules is, and what behavior you would expect? This would
> > allow to better understand what you are trying to achieve. The more
> > context you can give, the easier it is to understand what happens
> > there.
> >
>
> Sorry it's not very clear, so the difference between the cases is that
> in the case of UHID the report ID ends up being included as a part of
> "SET_FEATURE", so BlueZ checks UHID_DEV_NUMBERED_FEATURE_REPORTS,
> which is not set (correctly) and tries to send the whole payload. This
> ends up as a maxlen + 1 (extra byte) write to a property that is
> maxlen long, which gets rejected by device's BLE stack.
>
> In the case of USBHID the problem happens in "GET_FEATURE" path. When
> userspace reads the expected data back it gets an extra 0 prepended to
> the payload, so all of the actual payload has an offset of 1. This
> doesn't happen with UHID, which I think is the correct behavior here.
>
> Hopefully that explains the difference, let me know if something is unclear
Yes, thanks, I completely missed that. Lets continue discussion on the patches.
Thanks!
David