Re: [PATCH] input: change SysRq keycode for systems without SysRq key

On Fri, 20 Jul 2007, federico ferri wrote:

oh, great! finally I got to remap F13 to SysRq (which was keycode 99). 
would be nice to have some informations in the manpage about how to 
find/dump those raw scancodes, cause with showkey/evtest I only see 
translated keycodes. [I added keyfuzz's author to CC ;)]

Hi Federico,

JFYI - actually Marvin (added to CC) requested that the hid driver (i.e. 
USB keyboards, etc.) would report also HID usage codes through evdev 
(exactly to suit the use cases similar to your situation).

Quoting below an excerpt from the mail I sent him some time ago on this 
matter:

**

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 7f81789..c604a1d 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c

@@ -818,6 +818,11 @@ static void hidinput_configure_usage(struct hid_input *hidinput, struct hid_fiel
 			field->dpad = usage->code;
 	}
 
+	if (usage->type == EV_KEY) {
+		set_bit(EV_MSC, input->evbit);
+		set_bit(usage->code, input->mscbit);
+	}
+
 	hid_resolv_event(usage->type, usage->code);
 #ifdef CONFIG_HID_DEBUG
 	printk("\n");

@@ -908,6 +913,9 @@ void hidinput_hid_event(struct hid_device *hid, struct hid_field *field, struct
 	if ((usage->type == EV_KEY) && (usage->code == 0)) /* Key 0 is "unassigned", not KEY_UNKNOWN */
 		return;
 
+	if (usage->type == EV_KEY)
+		input_event(input, EV_MSC, MSC_SCAN, usage->hid);
+
 	input_event(input, usage->type, usage->code, value);
 
 	if ((field->flags & HID_MAIN_ITEM_RELATIVE) && (usage->type == EV_KEY))

There is an slight issue with this patch though. Imagine you have such a 
keyboard that sends in one field the status of Caps/Num/Shift/etc and in 
another field the pressed key(s) itself, i.e. something like this:

  INPUT[INPUT]
    Field(0)
      Usage(8)
        Keyboard.00e0
        Keyboard.00e1
        Keyboard.00e2
        Keyboard.00e3
        Keyboard.00e4
        Keyboard.00e5
        Keyboard.00e6
        Keyboard.00e7
      Logical Minimum(0)
      Logical Maximum(1)
      Report Size(1)
      Report Count(8)
      Report Offset(0)
      Flags( Variable Absolute )
... 

and then the next field is used to transfer the actual keys. Therefore, 
with this patch, hid-input sees a report containing usages e0-e7 set to 
zero (when no caps/num/shift/... was pressed). This results in evtest 
seeing this (with the patch below applied) for a single keypress:

Event: time 1182930853.026146, type 4 (Misc), code 4 (ScanCode), value 700e0
Event: time 1182930853.026159, type 4 (Misc), code 4 (ScanCode), value 700e1
Event: time 1182930853.026168, type 4 (Misc), code 4 (ScanCode), value 700e2
Event: time 1182930853.026178, type 4 (Misc), code 4 (ScanCode), value 700e3
Event: time 1182930853.026187, type 4 (Misc), code 4 (ScanCode), value 700e4
Event: time 1182930853.026197, type 4 (Misc), code 4 (ScanCode), value 700e5
Event: time 1182930853.026206, type 4 (Misc), code 4 (ScanCode), value 700e6
Event: time 1182930853.026216, type 4 (Misc), code 4 (ScanCode), value 700e7
Event: time 1182930853.026227, type 4 (Misc), code 4 (ScanCode), value 70004
Event: time 1182930853.026233, type 1 (Key), code 30 (A), value 1
Event: time 1182930853.026237, -------------- Report Sync ------------
Event: time 1182930853.114137, type 4 (Misc), code 4 (ScanCode), value 700e0
Event: time 1182930853.114150, type 4 (Misc), code 4 (ScanCode), value 700e1
Event: time 1182930853.114160, type 4 (Misc), code 4 (ScanCode), value 700e2
Event: time 1182930853.114169, type 4 (Misc), code 4 (ScanCode), value 700e3
Event: time 1182930853.114179, type 4 (Misc), code 4 (ScanCode), value 700e4
Event: time 1182930853.114188, type 4 (Misc), code 4 (ScanCode), value 700e5
Event: time 1182930853.114198, type 4 (Misc), code 4 (ScanCode), value 700e6
Event: time 1182930853.114207, type 4 (Misc), code 4 (ScanCode), value 700e7
Event: time 1182930853.114218, type 4 (Misc), code 4 (ScanCode), value 70004
Event: time 1182930853.114223, type 1 (Key), code 30 (A), value 0
Event: time 1182930853.114227, -------------- Report Sync ------------

I don't think this is what you want. We could alternatively for example 
remember all the previous states of all the KEY controls and report 
scancodes only of those which got changed, this would solve this issue.
**

However, this might look like an overhead.

-- 
Jiri Kosina