Re: [PATCH 1/4] usb: Don't enable USB 2.0 Link PM by default.

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On Mon, Sep 30, 2013 at 05:26:28PM +0300, Mathias Nyman wrote:
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  drivers/usb/core/driver.c   |    3 +
>  drivers/usb/core/sysfs.c    |    1 +
>  drivers/usb/host/xhci-mem.c |   10 ---
>  drivers/usb/host/xhci.c     |  152 +++----------------------------------------
>  include/linux/usb.h         |    4 +-
>  5 files changed, 16 insertions(+), 154 deletions(-)
> 
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index f7841d4..689433c 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1790,6 +1790,9 @@ int usb_set_usb2_hardware_lpm(struct usb_device *udev, int enable)
>  	struct usb_hcd *hcd = bus_to_hcd(udev->bus);
>  	int ret = -EPERM;
>  
> +	if (enable && !udev->usb2_hw_lpm_allowed)
> +		return 0;
> +
>  	if (hcd->driver->set_usb2_hw_lpm) {
>  		ret = hcd->driver->set_usb2_hw_lpm(hcd, udev, enable);
>  		if (!ret)
> diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
> index 6d2c8ed..76bce3a 100644
> --- a/drivers/usb/core/sysfs.c
> +++ b/drivers/usb/core/sysfs.c
> @@ -469,6 +469,7 @@ static ssize_t usb2_hardware_lpm_store(struct device *dev,
>  
>  	ret = strtobool(buf, &value);
>  
> +	udev->usb2_hw_lpm_allowed = value;
>  	if (!ret)
>  		ret = usb_set_usb2_hardware_lpm(udev, value);

On a second review, I see a bug here.  What happens if someone passes in
bad input?  udev->usb2_hw_lpm_allowed gets set to garbage.

Also, what should happen if usb_set_usb2_hardware_lpm() fails?  Should
we set udev->usb2_hw_lpm_allowed to the previously stored value?  I'll
have to double check what the code does in failure cases.

I'll refresh the patch shortly and send it out.

Sarah Sharp
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