diff mbox series

[RFC,v2,4/7] HID: i2c-hid: Move i2c_hid_finish_hwreset() to after reading the report-descriptor

Message ID 20231120193313.666912-5-hdegoede@redhat.com
State New
Headers show
Series HID: i2c-hid: Rework wait for reset to match Windows | expand

Commit Message

Hans de Goede Nov. 20, 2023, 7:33 p.m. UTC
A recent bug made me look at Microsoft's i2c-hid docs again
and I noticed the following:

"""
4. Issue a RESET (Host Initiated Reset) to the Device.
5. Retrieve report descriptor from the device.

Note: Steps 4 and 5 may be done in parallel to optimize for time on I²C.
Since report descriptors are (a) static and (b) quite long, Windows 8 may
issue a request for 5 while it is waiting for a response from the device
on 4.
"""

Which made me think that maybe on some touchpads the reset ack is delayed
till after the report descriptor is read ?

Testing a T-BAO Tbook Air 12.5 with a 0911:5288 (SIPODEV SP1064?) touchpad,
for which the I2C_HID_QUIRK_NO_IRQ_AFTER_RESET quirk was first introduced,
shows that reading the report descriptor before waiting for the reset
helps with the missing reset IRQ. Now the reset does get acked properly,
but the ack sometimes still does not happen unfortunately.

Still moving the wait for ack to after reading the report-descriptor,
is probably a good idea, both to make i2c-hid's behavior closer to
Windows as well as to speed up probing i2c-hid devices.

While at it drop the dbg_hid() for a malloc failure, malloc failures
already get logged extensively by malloc itself.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2247751
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v2:
- Adjust commit message to note that moving the wait-for-reset
  to after reading thr report-descriptor only partially fixes
  the missing reset IRQ problem
- Adjust for the reset_lock now being taken in the callers of
  i2c_hid_start_hwreset() / i2c_hid_finish_hwreset()
---
 drivers/hid/i2c-hid/i2c-hid-core.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

Comments

Doug Anderson Nov. 21, 2023, 3:25 p.m. UTC | #1
Hi,

On Tue, Nov 21, 2023 at 1:53 AM Hans de Goede <hdegoede@redhat.com> wrote:
>
> > Right after this loop, you have:
> >
> > if (ret)
> >   return ret;
> >
> > That will return with the mutex held. It needs to be a "goto
> > abort_reset". You'd also need to init `use_override` then, I think.
>
> Ah, good catch, I will fix this for the next version.
>
> Assuming there will be a next version. Did you read the cover-letter
> part about the moving of the wait for reset to after the descriptor
> read not fixing the missing reset ack 100% but rather only 50% or
> so of the time ?
>
> And do you have any opinion on if we should still move forward with
> this patch-set or not ?

I'd tend to leave it to your judgement. I have a bias towards landing
it because it improves probe speed in a way that matches what the spec
suggests and, IMO, probe speed is important. It also has the potential
to avoid the need for quirks on some devices, even if it didn't work
out that way for the device you tested with.

The only downside you have listed is the potential for regressions,
but that's something that's a risk for nearly any change. This doesn't
feel like an excessively risky change to me and, as you've pointed
out, it's documented in the spec. If someone reports a regression then
it seems like we should address it as it comes...


> > I'll also note that it seems awkward that
> > `clear_bit(I2C_HID_RESET_PENDING, &ihid->flags)` is scattered in so
> > many places for error handling, but I couldn't really find a better
> > way to do it. :-P
>
> I guess we could just no clear it? Only the wait for reset
> wait_event_timeout() cares about its value and if we run that
> a second time then the bit will be set to 1 again before calling
> it anyways...    Not sure I like my own suggestion here, but
> it is an option. I'm afraid it may bite us later thogh if we
> ever decide to check for the bit in another place.

Yeah, I didn't have any great ideas either and I think it's fine as
you have it. It just bothered me as I was reviewing and so I figured
I'd mention it in case some brilliant idea occurred to you. ;-)
Hans de Goede Nov. 21, 2023, 4:05 p.m. UTC | #2
Hi,

On 11/21/23 16:25, Doug Anderson wrote:
> Hi,
> 
> On Tue, Nov 21, 2023 at 1:53 AM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>>> Right after this loop, you have:
>>>
>>> if (ret)
>>>   return ret;
>>>
>>> That will return with the mutex held. It needs to be a "goto
>>> abort_reset". You'd also need to init `use_override` then, I think.
>>
>> Ah, good catch, I will fix this for the next version.
>>
>> Assuming there will be a next version. Did you read the cover-letter
>> part about the moving of the wait for reset to after the descriptor
>> read not fixing the missing reset ack 100% but rather only 50% or
>> so of the time ?
>>
>> And do you have any opinion on if we should still move forward with
>> this patch-set or not ?
> 
> I'd tend to leave it to your judgement. I have a bias towards landing
> it because it improves probe speed in a way that matches what the spec
> suggests and, IMO, probe speed is important.

I'm tending towards still merging this myself too. So when I've some
time I'll address your remarks and post a non RFC v3.

Regards,

Hans
diff mbox series

Patch

diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i2c-hid-core.c
index 5e535480fed7..48582c75a51b 100644
--- a/drivers/hid/i2c-hid/i2c-hid-core.c
+++ b/drivers/hid/i2c-hid/i2c-hid-core.c
@@ -741,12 +741,9 @@  static int i2c_hid_parse(struct hid_device *hid)
 		return -EINVAL;
 	}
 
+	mutex_lock(&ihid->reset_lock);
 	do {
-		mutex_lock(&ihid->reset_lock);
 		ret = i2c_hid_start_hwreset(ihid);
-		if (ret == 0)
-			ret = i2c_hid_finish_hwreset(ihid);
-		mutex_unlock(&ihid->reset_lock);
 		if (ret)
 			msleep(1000);
 	} while (tries-- > 0 && ret);
@@ -764,8 +761,8 @@  static int i2c_hid_parse(struct hid_device *hid)
 		rdesc = kzalloc(rsize, GFP_KERNEL);
 
 		if (!rdesc) {
-			dbg_hid("couldn't allocate rdesc memory\n");
-			return -ENOMEM;
+			ret = -ENOMEM;
+			goto abort_reset;
 		}
 
 		i2c_hid_dbg(ihid, "asking HID report descriptor\n");
@@ -775,10 +772,23 @@  static int i2c_hid_parse(struct hid_device *hid)
 					    rdesc, rsize);
 		if (ret) {
 			hid_err(hid, "reading report descriptor failed\n");
-			goto out;
+			goto abort_reset;
 		}
 	}
 
+	/*
+	 * Windows directly reads the report-descriptor after sending reset
+	 * and then waits for resets completion afterwards. Some touchpads
+	 * actually wait for the report-descriptor to be read before signalling
+	 * reset completion.
+	 */
+	ret = i2c_hid_finish_hwreset(ihid);
+abort_reset:
+	clear_bit(I2C_HID_RESET_PENDING, &ihid->flags);
+	mutex_unlock(&ihid->reset_lock);
+	if (ret)
+		goto out;
+
 	i2c_hid_dbg(ihid, "Report Descriptor: %*ph\n", rsize, rdesc);
 
 	ret = hid_parse_report(hid, rdesc, rsize);