Report ID of zero is a special case handling ID-less reports and in
that case we should omit report ID from the payload being sent to the
backend.
Without this change UHID_DEV_NUMBERED_{FEATURE,OUTPUT}_REPORTS doesn't
represent a semantical difference.
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/uhid.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 2a918aeb0af1..7551120215e8 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -273,11 +273,11 @@ static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
}
static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
- const u8 *buf, size_t count, u8 rtype)
+ u8 *buf, size_t count, u8 rtype)
{
struct uhid_device *uhid = hid->driver_data;
struct uhid_event *ev;
- int ret;
+ int ret, skipped_report_id = 0;
if (!READ_ONCE(uhid->running) || count > UHID_DATA_MAX)
return -EIO;
@@ -286,6 +286,15 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
if (!ev)
return -ENOMEM;
+ /* Byte 0 is the report number. Report data starts at byte 1.*/
+ buf[0] = rnum;
+ if (buf[0] == 0x0) {
+ /* Don't send the Report ID */
+ buf++;
+ count--;
+ skipped_report_id = 1;
+ }
+
ev->type = UHID_SET_REPORT;
ev->u.set_report.rnum = rnum;
ev->u.set_report.rtype = rtype;
@@ -306,7 +315,7 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
if (uhid->report_buf.u.set_report_reply.err)
ret = -EIO;
else
- ret = count;
+ ret = count + skipped_report_id;
unlock:
mutex_unlock(&uhid->report_lock);
--
2.34.1
Hi
On Mon, 5 Dec 2022 at 22:04, Andrey Smirnov <[email protected]> wrote:
>
> Report ID of zero is a special case handling ID-less reports and in
> that case we should omit report ID from the payload being sent to the
> backend.
>
> Without this change UHID_DEV_NUMBERED_{FEATURE,OUTPUT}_REPORTS doesn't
> represent a semantical difference.
>
> 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/uhid.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
> index 2a918aeb0af1..7551120215e8 100644
> --- a/drivers/hid/uhid.c
> +++ b/drivers/hid/uhid.c
> @@ -273,11 +273,11 @@ static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
> }
>
> static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
> - const u8 *buf, size_t count, u8 rtype)
> + u8 *buf, size_t count, u8 rtype)
> {
> struct uhid_device *uhid = hid->driver_data;
> struct uhid_event *ev;
> - int ret;
> + int ret, skipped_report_id = 0;
>
> if (!READ_ONCE(uhid->running) || count > UHID_DATA_MAX)
> return -EIO;
> @@ -286,6 +286,15 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
> if (!ev)
> return -ENOMEM;
>
> + /* Byte 0 is the report number. Report data starts at byte 1.*/
> + buf[0] = rnum;
> + if (buf[0] == 0x0) {
> + /* Don't send the Report ID */
> + buf++;
> + count--;
> + skipped_report_id = 1;
> + }
> +
In HID core, the buffer is filled by a call to hid_output_report() in
__hid_request(). And hid_output_report() only writes the ID if it is
non-zero. So your patch looks like it is duplicating this logic? In
which scenario is the report-ID not skipped exactly?
Regardless, if you want to mess with the buffer, you should do that
after the memcpy(). I don't see why we should mess with the buffer
from HID core, when we have our own, anyway.
David
)
On Mon, Dec 12, 2022 at 7:23 AM David Rheinsberg
<[email protected]> wrote:
>
> Hi
>
> On Mon, 5 Dec 2022 at 22:04, Andrey Smirnov <[email protected]> wrote:
> >
> > Report ID of zero is a special case handling ID-less reports and in
> > that case we should omit report ID from the payload being sent to the
> > backend.
> >
> > Without this change UHID_DEV_NUMBERED_{FEATURE,OUTPUT}_REPORTS doesn't
> > represent a semantical difference.
> >
> > 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/uhid.c | 15 ++++++++++++---
> > 1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
> > index 2a918aeb0af1..7551120215e8 100644
> > --- a/drivers/hid/uhid.c
> > +++ b/drivers/hid/uhid.c
> > @@ -273,11 +273,11 @@ static int uhid_hid_get_report(struct hid_device *hid, unsigned char rnum,
> > }
> >
> > static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
> > - const u8 *buf, size_t count, u8 rtype)
> > + u8 *buf, size_t count, u8 rtype)
> > {
> > struct uhid_device *uhid = hid->driver_data;
> > struct uhid_event *ev;
> > - int ret;
> > + int ret, skipped_report_id = 0;
> >
> > if (!READ_ONCE(uhid->running) || count > UHID_DATA_MAX)
> > return -EIO;
> > @@ -286,6 +286,15 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
> > if (!ev)
> > return -ENOMEM;
> >
> > + /* Byte 0 is the report number. Report data starts at byte 1.*/
> > + buf[0] = rnum;
> > + if (buf[0] == 0x0) {
> > + /* Don't send the Report ID */
> > + buf++;
> > + count--;
> > + skipped_report_id = 1;
> > + }
> > +
>
> In HID core, the buffer is filled by a call to hid_output_report() in
> __hid_request(). And hid_output_report() only writes the ID if it is
> non-zero. So your patch looks like it is duplicating this logic?
It would be in this scenario. But then I think it also means that
USBHID will incorrectly strip an extra byte of the payload if it's
zero for reports that don't have a report id, right? So maybe the fix
for this is to get rid of payload adjustment in set/send paths in
USBHID and move the adjustment to hidraw?
> In which scenario is the report-ID not skipped exactly?
The call chain in my use case is as follows:
hidraw_ioctl(HIDIOCSFEATURE) -> hid_hw_raw_request() ->
uhid_hid_raw_request() -> uhid_hid_set_report()
>
> Regardless, if you want to mess with the buffer, you should do that
> after the memcpy(). I don't see why we should mess with the buffer
> from HID core, when we have our own, anyway.
>
I was just mimicking code from USBHID, to make it clear it served the
same purpose, that
buf[0] = rnum;
isn't strictly necessary and could be dropped.