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Date:	Sat, 13 Jun 2015 08:12:35 +0800
From:	"Lu, Baolu" <baolu.lu@...ux.intel.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] usb: core: lpm: set lpm_capable for root hub device



On 06/13/2015 01:43 AM, Alan Stern wrote:
> On Fri, 12 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@...r.kernel.org # 3.15
>> Reported-by: Kevin Strasser <kevin.strasser@...ux.intel.com>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/usb/core/hcd.c | 6 ++++++
>>   drivers/usb/core/hub.c | 2 +-
>>   drivers/usb/core/usb.h | 1 +
>>   3 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
>> index 45a915c..48b208d 100644
>> --- a/drivers/usb/core/hcd.c
>> +++ b/drivers/usb/core/hcd.c
>> @@ -1032,6 +1032,12 @@ static int register_root_hub(struct usb_hcd *hcd)
>>   		}
>>   	}
>>   
>> +	if (le16_to_cpu(usb_dev->descriptor.bcdUSB) >= 0x0201) {
>> +		retval = usb_get_bos_descriptor(usb_dev);
>> +		if (!retval)
>> +			usb_dev->lpm_capable = usb_device_supports_lpm(usb_dev);
>> +	}
>> +
> This should be integrated with the code immediately above it, which
> also calls usb_get_bos_descriptor().  In fact, maybe you should simply
> change the existing code to check bcdUSB >= 0x0201 instead of speed ==
> USB_SPEED_SUPER.

I agree with you and will change it in v2 patch.

>
>>   	retval = usb_new_device (usb_dev);
>>   	if (retval) {
>>   		dev_err (parent_dev, "can't register root hub for %s, %d\n",
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index 3b71516..884d702 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -122,7 +122,7 @@ struct usb_hub *usb_hub_to_struct_hub(struct usb_device *hdev)
>>   	return usb_get_intfdata(hdev->actconfig->interface[0]);
>>   }
>>   
>> -static int usb_device_supports_lpm(struct usb_device *udev)
>> +int usb_device_supports_lpm(struct usb_device *udev)
>>   {
>>   	/* USB 2.1 (and greater) devices indicate LPM support through
>>   	 * their USB 2.0 Extended Capabilities BOS descriptor.
>> diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
>> index 7eb1e26..d5668c4 100644
>> --- 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
> This will break if you build it with CONFIG_PM disabled.

Yes. Will fix it in v2 patch.

>
> Alan Stern

Thank you,
Baolu

>
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