usb: hub: Per-port setting to use old enumeration scheme

The "old" enumeration scheme is considerably faster (it takes
~244ms instead of ~356ms to get the descriptor).

It is currently only possible to use the old scheme globally
(/sys/module/usbcore/parameters/old_scheme_first), which is not
desirable as the new scheme was introduced to increase compatibility
with more devices.

However, in our case, we care about time-to-active for a specific
USB device (which we make the firmware for), on a specific port
(that is pogo-pin based: not a standard USB port). This new
sysfs option makes it possible to use the old scheme on a single
port only.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index 6979bde87d31..4a2143195395 100644
--- a/drivers/usb/core/port.c
+++ b/drivers/usb/core/port.c
@@ -50,6 +50,28 @@ static ssize_t over_current_count_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(over_current_count);
 
+static ssize_t quirks_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct usb_port *port_dev = to_usb_port(dev);
+
+	return sprintf(buf, "%08x\n", port_dev->quirks);
+}
+
+static ssize_t quirks_store(struct device *dev, struct device_attribute *attr,
+			    const char *buf, size_t count)
+{
+	struct usb_port *port_dev = to_usb_port(dev);
+	u32 value;
+
+	if (kstrtou32(buf, 16, &value))
+		return -EINVAL;
+
+	port_dev->quirks = value;
+	return count;
+}
+static DEVICE_ATTR_RW(quirks);
+
 static ssize_t usb3_lpm_permit_show(struct device *dev,
 			      struct device_attribute *attr, char *buf)
 {
@@ -118,6 +140,7 @@ static DEVICE_ATTR_RW(usb3_lpm_permit);
 
 static struct attribute *port_dev_attrs[] = {
 	&dev_attr_connect_type.attr,
+	&dev_attr_quirks.attr,
 	&dev_attr_over_current_count.attr,
 	NULL,
 };