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

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Message-ID: <Pine.LNX.4.44L0.1506121334110.1505-100000@iolanthe.rowland.org>
Date:	Fri, 12 Jun 2015 13:43:13 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lu Baolu <baolu.lu@...ux.intel.com>
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 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.

>  	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.

Alan Stern

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