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Date: Fri, 20 Nov 2020 04:58:24 -0800
From: Nick Owens <mischief@offblast.org>
To: 9front@9front.org
Subject: bug: nusb fails to set report protocol with a stall error
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X-Bullshit: ISO-certified callback-based XMPP over ActivityPub high-performance extension 

on my desktop with usb3, i see 'setproto: Stall Error' with certain
devices.

when using nusb/kb with my tex shinobi, i see a stall error, but only
for the builtin trackpoint.

when using nusb/joy i see a stall error with my ps4 controller.

with a short test, i just removed the command to set the interface
protocol, and now both devices work.

after looking at the HID 1.11 spec, it seems like if a HID interface
descriptor has an interface subclass of 0, support for set protocol is
optional.

here is a patch which avoids setproto for devices which might not
support it, and it works for both my tex shinobi and ps4 controller.

thoughts?

diff --git a/sys/src/cmd/nusb/joy/joy.c b/sys/src/cmd/nusb/joy/joy.c
--- a/sys/src/cmd/nusb/joy/joy.c
+++ b/sys/src/cmd/nusb/joy/joy.c
@@ -222,6 +222,12 @@ setproto(KDev *f, int eid)
 		proto = Reportproto;
 	}else
 		kbfatal(f, "no report");
+
+	// if a HID's subclass code is 0, it may not support setproto,
+	// and is always initialized in report mode.
+	if(((iface->csp>>8)&0xFF) == 0)
+		return 0;
+
 	return usbcmd(f->dev, Rh2d|Rclass|Riface, Setproto, proto, id, nil, 0);
 }
 
diff --git a/sys/src/cmd/nusb/kb/kb.c b/sys/src/cmd/nusb/kb/kb.c
--- a/sys/src/cmd/nusb/kb/kb.c
+++ b/sys/src/cmd/nusb/kb/kb.c
@@ -368,6 +368,12 @@ setproto(Hiddev *f, int eid)
 		}
 		proto = Bootproto;
 	}
+
+	// if a HID's subclass code is 0, it may not support setproto,
+	// and is always initialized in report mode.
+	if(((iface->csp>>8)&0xFF) == 0)
+		return 0;
+
 	return usbcmd(f->dev, Rh2d|Rclass|Riface, Setproto, proto, iface->id, nil, 0);
 }