Re: [PATCH v2 1/1] usb: core: lpm: set lpm_capable for root hub device

["Lu, Baolu" <baolu.lu@linux.intel.com>]

On 06/13/2015 11:00 PM, Alan Stern wrote:
> On Sat, 13 Jun 2015, Lu Baolu wrote:
>
>> Commit 25cd2882e2fc ("usb/xhci: Change how we indicate a host supports
>> Link PM.") removed the code to set lpm_capable for USB 3.0 super-speed
>> root hub. The intention of that change was to avoid touching usb core
>> internal field, a.k.a. lpm_capable, and let usb core to set it by
>> checking U1 and U2 exit latency values in the descriptor.
>>
>> Usb core checks and sets lpm_capable in hub_port_init(). Unfortunately,
>> root hub is a special usb device as it has no parent. Hub_port_init()
>> will never be called for a root hub device. That means lpm_capable will
>> by no means be set for the root hub. As the result, lpm isn't functional
>> at all in Linux kernel.
>>
>> This patch add the code to check and set lpm_capable when registering a
>> root hub device. It could be back-ported to kernels as old as v3.15,
>> that contains the Commit 25cd2882e2fc ("usb/xhci: Change how we indicate
>> a host supports Link PM.").
>>
>> Cc: stable@vger.kernel.org # 3.15
>> Reported-by: Kevin Strasser <kevin.strasser@linux.intel.com>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> --- a/drivers/usb/core/usb.h
>> +++ b/drivers/usb/core/usb.h
>> @@ -82,6 +82,7 @@ extern int usb_runtime_suspend(struct device *dev);
>>   extern int usb_runtime_resume(struct device *dev);
>>   extern int usb_runtime_idle(struct device *dev);
>>   extern int usb_set_usb2_hardware_lpm(struct usb_device *udev, int enable);
>> +extern int usb_device_supports_lpm(struct usb_device *udev);
>>   
>>   #else
>>   
>> @@ -106,6 +107,11 @@ static inline int usb_set_usb2_hardware_lpm(struct usb_device *udev, int enable)
>>   	return 0;
>>   }
>>   
>> +static inline int usb_device_supports_lpm(struct usb_device *udev)
>> +{
>> +	return 0;
>> +}
>> +
>>   #endif
>>   
>>   extern struct bus_type usb_bus_type;
> In fact, usb_device_supports_lpm() is compiled even when CONFIG_PM
> isn't set.  Maybe this should be changed.  But if you don't want to
> change it now, you need to put the declaration outside the "#ifdef
> CONFIG_PM" region.  As it is, your patch is still broken (did you try
> building it with CONFIG_PM unset?).

I am sorry for this silly mistake. I will move it out of CONFIG_PM region.

I tried building with CONFIG_PM unset. But it turns out that CONFIG_PM
was auto selected by some other items. I will test my next version of
patch with CONFIG_PM *really* unset before sending it out.

Thanks,
Baolu

>
> Alan Stern
>
>