Re: Busted keyboard, fix, and Question about default HID device plumbing

Whoops. Flip those last two bit decodes!

-- Terry

On Fri, Oct 7, 2011 at 4:01 PM, Terry Lambert [off-list ref] wrote:

Thanks for replying, Dmitry...

I guess I need to clarify a point or two.

On Fri, Oct 7, 2011 at 3:07 PM, Dmitry Torokhov
[off-list ref] wrote:

quoted

Hi Terry,

On Fri, Oct 07, 2011 at 01:44:29PM -0700, Terry Lambert wrote:

quoted

I have a USB keyboard that needs a workaround.  I know what the
workaround is, but not where to plumb it in.

This is apparently an issue with a number of keyboards from a number
of vendors, and Mac OS X and Windows both work around it.  It impacts
all Linux desktops, Android, and Chrome OS for a number of popular
folding keyboards, as well as other keyboards.

I'm perfectly able to write the workaround, and have done so using the
boot protocol, but now I want to fix the issue in the default stack
used for the console.

I don't care about the UHCI/EHCI plumbing, or anything up to hiddev;
but from there it gets murky as to how an event in the raw driver ends
up getting turned into a keyboard key.  It appears to be lost in
callbacks I'm having a hard time tracing through.

I've read three books on the Linux USB system, two of them very out of
date, and they're all written from the perspective of "So, you want to
write a device driver", rather than the perspective of "This book
documents the plumbing between the driver and userspace and how to
figure it out".

So the question is: how are things plumbed between hiddev and the
console driver,

They aren't. Or maybe we are talking about different "hiddev"s. The
generic HID driver binds devices to hid-input which registers them with
input core as separate input devices. The legacy console registers a
separate input handler (see drivers/tty/vt/keyboard.c) that binds to all
keyboard-like devices, listens to input events and converts them to
keystrokes and sends them to tty.

My question is "who processes USB report packets from a USB keyboard
into EV_KEY events?"

I understand that there's a separate evdev handler that publishes raw
events as /dev/input/eventX.  It's handling the events from somewhere,
but it's not clear to me how a hidraw1 event turns into a console
input event.

Somewhere someone is translating a USB 1.11 section 8.3 report into an
EV_KEY, and I need to do the modifier magic to alter the contents of
the reports before it gets to whoever that is.
You seem to be saying hid-input.c ... but I'm not seeing the modifier
bits being processed out of the report?

quoted

There is also a evdev input handler (that's where evtest utility gets
its data from) that provides input event data to userspace via
/dev/input/eventX nodes where X picks it does its own thing with it.

quoted

so I can figure out where I need to hack on the
events.

I just need to know the correct place/method to interpose the events.

Any help would be appreciated.

Thanks,
-- Terry

PS: For the curious:

I put a USB protocol analyzer on this thing, and discovered the problem.

The issue is that modifier keys are not reported in the bitmap on the
keyboard, and are instead signaled as in-band key events themselves.
The Mac OS X and Windows drivers work around the issue by
pre-processing the event stream looking for in-band modifier keys, and
then converting them into bit-sets in the (0'ed) bitmap of modifier
keys, and then dropping them from the key event stream.  Without the
workaround, the report order is such that it looks like a modifier up
report followed by a keystroke.  Here's evtest output for the sequence
after processing by the (unknown to me -- that's what I'm trying to
find out) code:

Event: time 1318019769.922534, type 4 (Misc), code 4 (ScanCode), value 700e1
Event: time 1318019769.922550, type 1 (Key), code 42 (LeftShift), value 1
Event: time 1318019769.922554, -------------- Report Sync ------------
Event: time 1318019770.082521, type 4 (Misc), code 4 (ScanCode), value
700e1 XXXX
Event: time 1318019770.082534, type 1 (Key), code 42 (LeftShift),
value 0          XXXX

Hmm, so the shift is reported as released before we get the next key...
Wierd...

quoted

Event: time 1318019770.082549, type 4 (Misc), code 4 (ScanCode), value 7001e
Event: time 1318019770.082553, type 1 (Key), code 2 (1), value 1
Event: time 1318019770.082555, -------------- Report Sync ------------
1Event: time 1318019770.242541, type 4 (Misc), code 4 (ScanCode), value 7001e
Event: time 1318019770.242552, type 1 (Key), code 2 (1), value 0
Event: time 1318019770.242555, -------------- Report Sync ------------

This is a shift-1.

The patch for usbkbd.c looks like this:

diff --git a/drivers/hid/usbhid/usbkbd.c b/drivers/hid/usbhid/usbkbd.c
index 0658173..d22ecdb 100644
--- a/drivers/hid/usbhid/usbkbd.c
+++ b/drivers/hid/usbhid/usbkbd.c

@@ -2,6 +2,10 @@

  *  Copyright (c) 1999-2001 Vojtech Pavlik
  *
  *  USB HIDBP Keyboard support
+ *
+ * Device Class Definition for Human Interface Devices (HID) Version 1.11
+ * Section 8.3 describes the report formant.
+ * http://www.usb.org/developers/devclass_docs/HID1_11.pdf
  */

 /*

@@ -97,6 +101,16 @@ static void usb_kbd_irq(struct urb *urb)

                goto resubmit;
        }

+       /* Convert in-band modifier keys to modifier bits */
+       for (i = 2; i < 8; i++) {
+               if (kbd->new[i] >= 0xE0 && kbd->new[i] <= 0xE7) {
+                       kbd->new[0] |= (1 >> (kbd->new[i] - 0xE0));
+                       kbd->new[i] = 0;
+               }
+       }

Wait, why are you using usbkbd? Unless you have very compelling reason
you should be using hid & hid-input.

I fixed it there because it was accessible and a way to test the fix.
I'm also going to have to do something similar for coreboot/u-boot to
allow the keyboard to be used in the boot loader, so it's not wasted
effort, and it was an OK proof of concept.  So there was a good
reason.

I'm getting the impression from the above that the file I should be
looking in is:

   drivers/hid/hid-input.c

Where are the modifier bits being decoded there?  Maybe I'm just not
seeing something in front of me...

The analyzer reports the USB over the wire report as:

<-- left shift key down -->
   00 00 E1 00 00 00 00 00  <- transaction
   69 82 18  <- input packet
   48 00 00 E1 00 00 00 00 00 A8 45 <-- breakout : <--
       Keyboard LeftControl : 0b0
       Keyboard LeftShift : 0b0  <-- ***WRONG ***
       Keyboard LeftAlt : 0b0
       Keyboard LeftGUI : 0b0
       Keyboard RightControl : 0b0
       Keyboard RightShiftl : 0b0
       Keyboard RightAlt : 0b0
       Keyboard RightGUI : 0b0
       Keyboard/Keypad Array : Keyboard LeftShift (225) <-- ***WRONG ***
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
   -->
<-- 1 key down -->
   00 00 E1 1E 00 00 00 00  <- transaction
   69 82 18  <- input packet
   C3 00 00 E1 1E 00 00 00 00 A8 45 <-- breakout : <--
       Keyboard LeftControl : 0b0
       Keyboard LeftShift : 0b0  <-- ***WRONG ***
       Keyboard LeftAlt : 0b0
       Keyboard LeftGUI : 0b0
       Keyboard RightControl : 0b0
       Keyboard RightShiftl : 0b0
       Keyboard RightAlt : 0b0
       Keyboard RightGUI : 0b0
       Keyboard/Keypad Array : Keyboard LeftShift (d225)  <-- *** WRONG ***
       Keyboard/Keypad Array : Keyboard 1 and ! (d30)
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
   -->
<-- 1 key up -- >
   00 00 E1 00 00 00 00 00  <- transaction
   69 82 18  <- input packet
   48 00 00 E1 00 00 00 00 00 A8 45 <-- breakout : <--
       Keyboard LeftControl : 0b0
       Keyboard LeftShift : 0b0
       Keyboard LeftAlt : 0b0
       Keyboard LeftGUI : 0b0
       Keyboard RightControl : 0b0
       Keyboard RightShiftl : 0b0
       Keyboard RightAlt : 0b0
       Keyboard RightGUI : 0b0
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
       Keyboard/Keypad Array : 00
   -->
<-- left shift key up -->
   00 00 00 00 00 00 00 00  <- transaction
   69 82 18  <- input packet
   48 00 00 00 00 00 00 00 00 BF F4 <-- breakout : <--
       Keyboard LeftControl : 0b0
       Keyboard LeftShift : 0b0  <-- ***WRONG ***
       Keyboard LeftAlt : 0b0
       Keyboard LeftGUI : 0b0
       Keyboard RightControl : 0b0
       Keyboard RightShiftl : 0b0
       Keyboard RightAlt : 0b0
       Keyboard RightGUI : 0b0
       Keyboard/Keypad Array : Keyboard LeftShift (225) <-- ***WRONG ***
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
       Keyboard/Keypad Array :
   -->

I just need to know where in the code to stomp the report into
correctness. Should make a bunch of people happy. 8-)

Thanks,
-- Terry

quoted

Thanks.

--
Dmitry

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