[Qemu-devel] [PATCH v3] hw/usb/dev-hid: Improve guest compatibility of usb-tablet

[Phil Dennis-Jordan]

 1. Set bInterfaceProtocol to 0x00 for usb-tablet. This should be non-zero for 
boot protocol devices only, which the usb-tablet is not.
 2. Set the usb-tablet's usage to "mouse" in the report descriptor.

The boot protocol of 0x02 specifically confused OS X/macOS' HID driver stack, 
causing it to generate additional bogus HID events with relative motion in 
addition to the tablet's absolute coordinate events.

Absolute pointing devices with HID Report Descriptor usage of 0x01 (pointing) 
are treated by the macOS HID driver as analog sticks, and absolute coordinates 
are not directly translated to absolute mouse cursor positions. Changing it to 
0x02 (mouse) fixes the problem, and does not have any adverse effect in other 
operating systems and windowing systems. (VMWare does the same thing.)

Signed-off-by: Phil Dennis-Jordan <address@hidden>
---

Changelog
=========

v2 -> v3:
 * v2 Thread was "[PATCH v2 0/2] hw/usb/dev-hid: Make usb-tablet work with OS 
X/macOS guests"
 * Changing the report descriptor to 0x02 (mouse) does not seem to have an 
adverse effect on any guests, so just change it for everyone instead of adding 
an option.
 * The 2 patches are now tiny, so combine them back into one.

v1 -> v2:
 * v1 Thread was "[PATCH] hw/usb/dev-hid: add a Mac guest compatibility option 
to usb-tablet"
 * Always apply the boot protocol (bInterfaceProtocol) change to usb-tablet, 
not just when the Mac compatibility option is active. The original value of 
0x02 was determined to be incorrect according to the spec anyway.
 * As the boot protocol change is permanent, separate interface and device 
descriptor constants for the Mac/non-Mac variants of the tablet are no longer 
required, and have been removed.


 hw/usb/dev-hid.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/hw/usb/dev-hid.c b/hw/usb/dev-hid.c
index 24d05f7..dda0bf0 100644
--- a/hw/usb/dev-hid.c
+++ b/hw/usb/dev-hid.c
@@ -144,7 +144,7 @@ static const USBDescIface desc_iface_tablet = {
     .bInterfaceNumber              = 0,
     .bNumEndpoints                 = 1,
     .bInterfaceClass               = USB_CLASS_HID,
-    .bInterfaceProtocol            = 0x02,
+    .bInterfaceProtocol            = 0x00,
     .ndesc                         = 1,
     .descs = (USBDescOther[]) {
         {
@@ -174,7 +174,7 @@ static const USBDescIface desc_iface_tablet2 = {
     .bInterfaceNumber              = 0,
     .bNumEndpoints                 = 1,
     .bInterfaceClass               = USB_CLASS_HID,
-    .bInterfaceProtocol            = 0x02,
+    .bInterfaceProtocol            = 0x00,
     .ndesc                         = 1,
     .descs = (USBDescOther[]) {
         {
@@ -487,7 +487,7 @@ static const uint8_t qemu_mouse_hid_report_descriptor[] = {
 
 static const uint8_t qemu_tablet_hid_report_descriptor[] = {
     0x05, 0x01,                /* Usage Page (Generic Desktop) */
-    0x09, 0x01,                /* Usage (Pointer) */
+    0x09, 0x02,                /* Usage (Mouse) */
     0xa1, 0x01,                /* Collection (Application) */
     0x09, 0x01,                /*   Usage (Pointer) */
     0xa1, 0x00,                /*   Collection (Physical) */
-- 
2.3.2 (Apple Git-55)