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.
> +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.
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?
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
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