usb: dwc3: gadget: let us set lower max_speed

In some SoCs, dwc3 is implemented as a USB2.0 only
core, meaning that it can't ever achieve SuperSpeed.

Currect driver always sets gadget.max_speed to
USB_SPEED_SUPER unconditionally. This can causes
issues to some Host stacks where the host will issue
a GetBOS() request and we will reply with a BOS
containing Superspeed Capability Descriptor.

At least Windows seems to be upset by this fact and
prints a warning that we should connect $this device
to another port.

[ balbi@ti.com : rewrote entire commit, including
source code comment to make a lot clearer what the
problem is ]

Cc: <stable@vger.kernel.org>
Signed-off-by: Ben McCauley <ben.mccauley@garmin.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 55ba447fdf8bf56720eeac029ed4f96d932ee0ea..e24a01cc98df4a43f2fd556e44b1557dce778d33 100644 (file)
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2744,11 +2744,33 @@ int dwc3_gadget_init(struct dwc3 *dwc)
        }
 
        dwc->gadget.ops                 = &dwc3_gadget_ops;
-       dwc->gadget.max_speed           = USB_SPEED_SUPER;
        dwc->gadget.speed               = USB_SPEED_UNKNOWN;
        dwc->gadget.sg_supported        = true;
        dwc->gadget.name                = "dwc3-gadget";
 
+       /*
+        * FIXME We might be setting max_speed to <SUPER, however versions
+        * <2.20a of dwc3 have an issue with metastability (documented
+        * elsewhere in this driver) which tells us we can't set max speed to
+        * anything lower than SUPER.
+        *
+        * Because gadget.max_speed is only used by composite.c and function
+        * drivers (i.e. it won't go into dwc3's registers) we are allowing this
+        * to happen so we avoid sending SuperSpeed Capability descriptor
+        * together with our BOS descriptor as that could confuse host into
+        * thinking we can handle super speed.
+        *
+        * Note that, in fact, we won't even support GetBOS requests when speed
+        * is less than super speed because we don't have means, yet, to tell
+        * composite.c that we are USB 2.0 + LPM ECN.
+        */
+       if (dwc->revision < DWC3_REVISION_220A)
+               dwc3_trace(trace_dwc3_gadget,
+                               "Changing max_speed on rev %08x\n",
+                               dwc->revision);
+
+       dwc->gadget.max_speed           = dwc->maximum_speed;
+
        /*
         * Per databook, DWC3 needs buffer size to be aligned to MaxPacketSize
         * on ep out.