linux-kernel - Re: [PATCH] usb: dwc3: Skip resume if pm_runtime_set

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Message-ID: <20250108011922.lmdafz3sqbbhbj6p@synopsys.com>
Date: Wed, 8 Jan 2025 01:19:25 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Ray Chi <raychi@...gle.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "albertccwang@...gle.com" <albertccwang@...gle.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pumahsu@...gle.com" <pumahsu@...gle.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: Skip resume if pm_runtime_set_active() fails

On Mon, Jan 06, 2025, Ray Chi wrote:
> When the system begins to enter suspend mode, dwc3_suspend() is called
> by PM suspend. There is a problem that if someone interrupt the system
> suspend process between dwc3_suspend() and pm_suspend() of its parent
> device, PM suspend will be canceled and attempt to resume suspended
> devices so that dwc3_resume() will be called. However, dwc3 and its
> parent device (like the power domain or glue driver) may already be
> suspended by runtime PM in fact. If this sutiation happened, the
> pm_runtime_set_active() in dwc3_resume() will return an error since
> parent device was suspended. This can lead to unexpected behavior if
> DWC3 proceeds to execute dwc3_resume_common().
> 
> EX.
> RPM suspend: ... -> dwc3_runtime_suspend()
>                       -> rpm_suspend() of parent device
> ...
> PM suspend: ... -> dwc3_suspend() -> pm_suspend of parent device
>                                  ^ interrupt, so resume suspended device
>           ...  <-  dwc3_resume()  <-/
>                       ^ pm_runtime_set_active() returns error
> 
> To prevent the problem, this commit will skip dwc3_resume_common() and
> return the error if pm_runtime_set_active() fails.


So, if the device is runtime suspended, we prevent any interrupt during
system suspend? Any way we can keep the same behavior and allow PM
interruption as when there's no runtime suspend.

BR,
Thinh