linux-kernel - Re: [PATCH 1/1] usb: core: lpm: set lpm

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Date:	Fri, 12 Jun 2015 14:14:50 +0800
From:	"Lu, Baolu" <baolu.lu@...ux.intel.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Mathias Nyman <mathias.nyman@...el.com>,
	Alan Stern <stern@...land.harvard.edu>,
	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 06/12/2015 12:32 PM, Greg Kroah-Hartman wrote:
> On Fri, Jun 12, 2015 at 09:29:37AM +0800, 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) {
> Why are you treating a binary coded value as a hex number to compare
> against?

The value of the bcdUSB field is 0xJJMN for version JJ.M.N, where
JJ – major version number,
M – minor version number,
N – sub-minor version number

I saw several places in usb core where it is treated as a hex and
check the version requirement like this. Do you want me to
separate it into three numbers and check major/minor/sub-minor
versions separately?

Thanks,
Baolu
>
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