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

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Date:	Thu, 11 Jun 2015 21:32:09 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Lu Baolu <baolu.lu@...ux.intel.com>
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 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?

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