linux-kernel - Re: [PATCH V5] USB: Increment wakeup count on remote wakeup.

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Date:   Fri, 20 Apr 2018 14:22:51 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Ravi Chandra Sadineni <ravisadineni@...omium.org>
cc:     gregkh@...uxfoundation.org, <martin.blumenstingl@...glemail.com>,
        <ravisadineni@...gle.com>, <chunfeng.yun@...iatek.com>,
        <johan@...nel.org>, <arvind.yadav.cs@...il.com>, <dtor@...gle.com>,
        <anton.bondarenko.sama@...il.com>, <f.fainelli@...il.com>,
        <keescook@...omium.org>, <mathias.nyman@...ux.intel.com>,
        <felipe.balbi@...ux.intel.com>, <ekorenevsky@...il.com>,
        <peter.chen@....com>, <joe@...ches.com>, <tbroch@...gle.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <rajatja@...gle.com>, <bleung@...gle.com>
Subject: Re: [PATCH V5] USB: Increment wakeup count on remote wakeup.

On Fri, 20 Apr 2018, Ravi Chandra Sadineni wrote:

> On chromebooks we depend on wakeup count to identify the wakeup source.
> But currently USB devices do not increment the wakeup count when they
> trigger the remote wake. This patch addresses the same.
> 
> Resume condition is reported differently on USB 2.0 and USB 3.0 devices.
> 
> On USB 2.0 devices, a wake capable device, if wake enabled, drives
> resume signal to indicate a remote wake (USB 2.0 spec section 7.1.7.7).
> The upstream facing port then sets C_PORT_SUSPEND bit and reports a
> port change event (USB 2.0 spec section 11.24.2.7.2.3). Thus if a port
> has resumed before driving the resume signal from the host and
> C_PORT_SUSPEND is set, then the device attached to the given port might
> be the reason for the last system wakeup. Increment the wakeup count for
> the same.
> 
> On USB 3.0 devices, a function may signal that it wants to exit from device
> suspend by sending a Function Wake Device Notification to the host (USB3.0
> spec section 8.5.6.4) Thus on receiving the Function Wake, increment the
> wakeup count.
> 
> Signed-off-by: Ravi Chandra Sadineni <ravisadineni@...omium.org>
> ---
> 
> V5: Added the description of changes between different versions of patches.
> V4: Moved the wakeup count increment logic to the existing if which is
> safegaurded by hcd_root_hub_lock spinlock.
> V3: Added a gaurd to check if rh_registered is set before accessing
> root_hub pointer.
> V2: Fixed the build failure error due to uninitialized dev pointer.

Acked-by: Alan Stern <stern@...land.harvard.edu>