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Subject[PATCH 4.3 096/125] usb: dwc3: gadget: let us set lower max_speed
Date
4.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben McCauley <ben.mccauley@garmin.com>

commit b9e51b2b1fda19143f48d182ed7a2943f21e1ae4 upstream.

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 ]

Signed-off-by: Ben McCauley <ben.mccauley@garmin.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/dwc3/gadget.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)

--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2723,12 +2723,34 @@ 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.
*/



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