linux-kernel - Re: [PATCH v2 1/3] usb: core: lpm: fix usb3_hardware

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Date:	Thu, 12 Nov 2015 11:20:14 -0500 (EST)
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>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] usb: core: lpm: fix usb3_hardware_lpm sysfs node

On Thu, 12 Nov 2015, Lu Baolu wrote:

> Commit 655fe4effe0f ("usbcore: add sysfs support to xHCI usb3
> hardware LPM") introduced usb3_hardware_lpm sysfs node. This
> doesn't show the correct status of USB3 U1 and U2 LPM status.
> 
> This patch fixes this by replacing usb3_hardware_lpm with two
> nodes, usb3_hardware_lpm_u1 (for U1) and usb3_hardware_lpm_u2
> (for U2), and recording the U1/U2 LPM status in right places.
> 
> This patch should be back-ported to kernels as old as 4.3,
> that contains Commit 655fe4effe0f ("usbcore: add sysfs support
> to xHCI usb3 hardware LPM").
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

...

> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -3875,17 +3875,23 @@ static void usb_enable_link_state(struct usb_hcd *hcd, struct usb_device *udev,
>  		return;
>  	}
>  
> -	if (usb_set_lpm_timeout(udev, state, timeout))
> +	ret = usb_set_lpm_timeout(udev, state, timeout);
> +	if (ret)
>  		/* If we can't set the parent hub U1/U2 timeout,
>  		 * device-initiated LPM won't be allowed either, so let the xHCI
>  		 * host know that this link state won't be enabled.
>  		 */
>  		hcd->driver->disable_usb3_lpm_timeout(hcd, udev, state);
> -
>  	/* Only a configured device will accept the Set Feature U1/U2_ENABLE */
>  	else if (udev->actconfig)
>  		usb_set_device_initiated_lpm(udev, state, true);
>  
> +	if (!ret) {
> +		if (state == USB3_LPM_U1)
> +			udev->usb3_lpm_u1_enabled = 1;
> +		else if (state == USB3_LPM_U2)
> +			udev->usb3_lpm_u2_enabled = 1;
> +	}

This doesn't look right at all.  What happens if ret is 0 but the
device isn't configured?  You'll set the usb3_lpm_u*_enabled flag even
though LPM isn't really enabled.

Don't you want to set these flags inside the
usb_set_device_initiated_lpm() function, where you know whether the
action succeeded?  And leave this routine unchanged?

> @@ -3925,6 +3931,12 @@ static int usb_disable_link_state(struct usb_hcd *hcd, struct usb_device *udev,
>  		dev_warn(&udev->dev, "Could not disable xHCI %s timeout, "
>  				"bus schedule bandwidth may be impacted.\n",
>  				usb3_lpm_names[state]);
> +
> +	if (state == USB3_LPM_U1)
> +		udev->usb3_lpm_u1_enabled = 0;
> +	else if (state == USB3_LPM_U2)
> +		udev->usb3_lpm_u2_enabled = 0;
> +
>  	return 0;
>  }

And then this won't be necessary.

Alan Stern

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