[PATCH v2 2/2] HID: input: do not increment usages when a duplicate is found

Benjamin Tissoires
2017-12-08T14:28:18Z

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>
---

changes in v2:
- fixed a bug where the flag was not used properly and prevented to
remove devices
- downgrade the error message from info to debug, given that when
hid-generic binds first, it will output such kernel log for every
multitouch device.

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 04d01b57d94c..31bbeb7019bd 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -1100,8 +1100,31 @@ 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;
@@ -1610,6 +1633,8 @@ 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];
@@ -1676,6 +1701,10 @@ int hidinput_connect(struct hid_device *hid, unsigned int force)
goto out_unwind;
}

+ if (hid->status & HID_STAT_DUP_DETECTED)
+ hid_dbg(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 421b62b77c69..de3a8700ccf1 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -344,6 +344,7 @@ 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
@@ -501,6 +502,7 @@ struct hid_output_fifo {

#define HID_STAT_ADDED BIT(0)
#define HID_STAT_PARSED BIT(1)
+#define HID_STAT_DUP_DETECTED BIT(2)

struct hid_input {
struct list_head list;
--
2.14.3