On 2012/6/29 22:16, Alan Stern wrote:
On Fri, 29 Jun 2012, Lan Tianyu wrote:
Change since v4: Add clear PORT_POWER if power policy is "off" in the
hub_power_on(). Return -EIO if set/clear PORT_POWER fails in the store_port_power_control()
This patch is to add two attributes for each usb hub ports to control port's power.
Control port's power through setting or clearing PORT_POWER feature.
control has two options. "auto", "on" and "off"
"on" - port power must be on.
"off" - port power must be off.
state reports usb port's power state
"on" - power on
"off" - power off
"error" - can't get power state
Signed-off-by: Lan Tianyu<tianyu.lan@xxxxxxxxx>
Some more thoughts on this...
+static ssize_t show_port_power_state(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct usb_device *udev = to_usb_device(dev->parent->parent);
+ int port1, power_state;
+ const char *result;
+
+ sscanf(dev_name(dev), "port%d",&port1);
+ power_state = usb_get_hub_port_power_state(udev, port1);
+ if (power_state == 1)
+ result = on_string;
+ else if (!power_state)
+ result = off_string;
+ else
+ result = "error";
+ return sprintf(buf, "%s\n", result);
+}
+static DEVICE_ATTR(state, S_IRUGO, show_port_power_state, NULL);
When this routine runs, the hub might be suspended. You should call
usb_autopm_get_interface before getting the power state and
usb_autopm_put_interface afterward.
Right. Thanks for your reminder.
+static ssize_t store_port_power_control(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t count)
+{
+ struct usb_device *hdev = to_usb_device(dev->parent->parent);
+ struct usb_port *hub_port = to_usb_port(dev);
+ int port1, ret, len = count;
+ char *cp;
+
+ sscanf(dev_name(dev), "port%d",&port1);
+ cp = memchr(buf, '\n', count);
+ if (cp)
+ len = cp - buf;
+ if (len == sizeof on_string - 1
+ && strncmp(buf, on_string, len) == 0) {
Please indent the continuation line an extra tab stop so that it
doesn't look like it's part of the body of the "if" statement.
+ hub_port->port_power_policy = USB_PORT_POWER_ON;
+ ret = set_port_feature(hdev, port1, USB_PORT_FEAT_POWER);
+ if (ret< 0)
+ return -EIO;
+ } else if (len == sizeof off_string - 1
+ && strncmp(buf, off_string, len) == 0) {
Same here.
+ hub_port->port_power_policy = USB_PORT_POWER_OFF;
+ ret = clear_port_feature(hdev, port1, USB_PORT_FEAT_POWER);
+ if (ret< 0)
+ return -EIO;
+ } else
+ return -EINVAL;
+
+ return count;
+}
The usb_autopm_* calls are also needed in this function.
In addition, what happens if a device is attached to a port when the
policy is changed to "off"? We probably want to make sure the device
gets disconnected when this happens. You should call
hub_port_logical_disconnect(hub, port1) before clearing the power
feature.
Ok.
Have you given any thought to locking? For example, what would happen
if the port power policy were changed at the same time as a new device
was plugged into the port?
Do you mean while a new device was enumerating, the port powered off? I
guess the enumerating process will fail.
My off-hand impression is that it won't matter and locking isn't
needed. But you should think about it more carefully.
Alan Stern
--
Best Regards
Tianyu Lan
linux kernel enabling team
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