linux-kernel - Re: [PATCH] usb: core: disable USB2 LPM when suspending

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Date:   Thu, 20 Sep 2018 10:43:40 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     AceLan Kao <acelan.kao@...onical.com>
cc:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Daniel Drake <drake@...lessm.com>,
        Joe Perches <joe@...ches.com>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: core: disable USB2 LPM when suspending

On Thu, 20 Sep 2018, AceLan Kao wrote:

> We found a S5 current leakage issue on Dell DW1820 WiFi/BT combo card
> which uses Qualcomm QCA6174 SoC. It also comes with WiFi and BT failure
> when encountered current leakage issue.
>    1. Power on, both WiFi and BT work.
>    2. Power off and found a current leakage issue(consumes ~0.5W)
>    3. Power on, no WiFi and BT devices can be found in lspci and lsusb.
>    4. Power off, there is no current leakage issue at S5.
>    5. continue to 1.
> 
> From Qualcomm's report:
> Based on the USB sniffer log, the difference between Linux and Windows
> is USB LPM setting(no LPM transaction on Windows) which may leads to
> the voltage leakage on Linux S5 state.
> 
> After checked the LPM related code and found, when system is going to
> enter S5, it resumes the USB devices from runtime suspend and enables
> USB2 LPM, and then it calls usb_dev_poweroff() -> usb_suspend(), and
> leave USB2 LPM stays enabled.

But usb_suspend() -> usb_suspend_both() -> usb_suspend_device() -> 
generic_suspend() -> usb_port_suspend() -> 
usb_set_usb2_hardware_lpm(udev, 0).  So why does USB2 LPM stay enabled?

> Disable USB2 LPM in usb_suspend() fixes the issue mentioned above,
> and try 30 times of s2idle, S3 and S5, the USB devices keep working
> well. Disable USB2 LPM seems do no harm to the system.
> 
> Signed-off-by: AceLan Kao <acelan.kao@...onical.com>
> ---
>  drivers/usb/core/driver.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index e76e95f62f76..ac5e60d7104f 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1463,6 +1463,9 @@ int usb_suspend(struct device *dev, pm_message_t msg)
>  	struct usb_device	*udev = to_usb_device(dev);
>  	int r;
>  
> +	if (udev->usb2_hw_lpm_enabled == 1)
> +		usb_set_usb2_hardware_lpm(udev, 0);

At this point the device may still be in runtime suspend.  Is that 
really okay?

Alan Stern

> +
>  	unbind_no_pm_drivers_interfaces(udev);
>  
>  	/* From now on we are sure all drivers support suspend/resume
>