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Subject[RFC] HID: input: do not increment usages when a duplicate is found
Date
This is something that bothered us from a long time. When hid-input
doesn't know how to map a usage, it uses *_MISC. But there is something
else which increments the usage if the evdev code is already used.

This leads to few issues:
- some devices may have their ABS_X mapped to ABS_Y if they export a bad
set of usages (see the DragonRise joysticks IIRC -> fixed in a specific
HID driver)
- *_MISC + N might (will) conflict with other defined axes (my Logitech
H800 exports some multitouch axes because of that)
- this prevents to freely add some new evdev usages, because "hey, my
headset will now report ABS_COFFEE, and it's not coffee capable".

So let's try to kill this nonsense, and hope we won't break too many
devices.

I my headset case, the ABS_MISC axes are created because of some
proprietary usages, so we might not break that many devices.

For backward compatibility, a quirk HID_QUIRK_INCREMENT_USAGE_ON_DUPLICATE
is created and can be applied to any device that needs this behavior.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
---

Hi,

well, given I'd like to have a formal "go" before spending too much time
in this, I am sending this a an RFC.
This won't solve all the user space problems (especially the detection of
non-mt devices based on ABS_MT_SLOT - 1 being set), but it should help us
extending the other event types.

Jiri, this patch applies on top of for-next + my series that creates
HID_QUIRK_HAVE_SPECIAL_DRIVER, so do not expect it to apply cleanly on your
tree :)

Cheers,
Benjamin

drivers/hid/hid-input.c | 33 +++++++++++++++++++++++++++++++--
include/linux/hid.h | 2 ++
2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index ccdff1e..9a9be89 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1025,8 +1025,31 @@ static void hidinput_configure_usage(struct hid_input *hidinput, struct hid_fiel

set_bit(usage->type, input->evbit);

- while (usage->code <= max && test_and_set_bit(usage->code, bit))
- usage->code = find_next_zero_bit(bit, max + 1, usage->code);
+ /*
+ * This part is *really* controversial:
+ * - HID aims at being generic so we should do our best to export
+ * all incoming events
+ * - HID describes what events are, so there is no reason for ABS_X
+ * to be mapped to ABS_Y
+ * - HID is using *_MISC+N as a default value, but nothing prevents
+ * *_MISC+N to overwrite a legitimate even, which confuses userspace
+ * (for instance ABS_MISC + 7 is ABS_MT_SLOT, which has a different
+ * processing)
+ *
+ * If devices still want to use this (at their own risk), they will
+ * have to use the quirk HID_QUIRK_INCREMENT_USAGE_ON_DUPLICATE, but
+ * the default should be a reliable mapping.
+ */
+ while (usage->code <= max && test_and_set_bit(usage->code, bit)) {
+ if (device->quirks & HID_QUIRK_INCREMENT_USAGE_ON_DUPLICATE) {
+ usage->code = find_next_zero_bit(bit,
+ max + 1,
+ usage->code);
+ } else {
+ device->status |= HID_STAT_DUP_DETECTED;
+ goto ignore;
+ }
+ }

if (usage->code > max)
goto ignore;
@@ -1527,6 +1550,8 @@ int hidinput_connect(struct hid_device *hid, unsigned int force)
INIT_LIST_HEAD(&hid->inputs);
INIT_WORK(&hid->led_work, hidinput_led_worker);

+ hid->status &= ~HID_STAT_DUP_DETECTED;
+
if (!force) {
for (i = 0; i < hid->maxcollection; i++) {
struct hid_collection *col = &hid->collection[i];
@@ -1593,6 +1618,10 @@ int hidinput_connect(struct hid_device *hid, unsigned int force)
goto out_unwind;
}

+ if (hid->status & HID_STAT_DUP_DETECTED)
+ hid_info(hid,
+ "Some usages could not be mapped, please use HID_QUIRK_INCREMENT_USAGE_ON_DUPLICATE if this is legitimate.\n");
+
return 0;

out_unwind:
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 7a473bf..245d1ac 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -340,6 +340,7 @@ struct hid_item {
#define HID_QUIRK_SKIP_OUTPUT_REPORT_ID 0x00020000
#define HID_QUIRK_NO_OUTPUT_REPORTS_ON_INTR_EP 0x00040000
#define HID_QUIRK_HAVE_SPECIAL_DRIVER 0x00080000
+#define HID_QUIRK_INCREMENT_USAGE_ON_DUPLICATE 0x00100000
#define HID_QUIRK_FULLSPEED_INTERVAL 0x10000000
#define HID_QUIRK_NO_INIT_REPORTS 0x20000000
#define HID_QUIRK_NO_IGNORE 0x40000000
@@ -491,6 +492,7 @@ struct hid_output_fifo {

#define HID_STAT_ADDED 1
#define HID_STAT_PARSED 2
+#define HID_STAT_DUP_DETECTED 3

struct hid_input {
struct list_head list;
--
2.9.4
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