linux-kernel - Re: [PATCH v4] PM: sleep: core: Avoid setting power.must

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Date:   Fri, 27 Aug 2021 10:57:59 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Prasad Sodagudi <psodagud@...eaurora.org>, rjw@...ysocki.net
Cc:     len.brown@...el.com, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, pavel@....cz
Subject: Re: [PATCH v4] PM: sleep: core: Avoid setting power.must_resume to
 false

On Mon, Aug 23, 2021 at 08:27:50AM -0700, Prasad Sodagudi wrote:
> There are variables(power.may_skip_resume and dev->power.must_resume)
> and DPM_FLAG_MAY_SKIP_RESUME flags to control the resume of devices after
> a system wide suspend transition.
> 
> Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver allows
> its "noirq" and "early" resume callbacks to be skipped if the device
> can be left in suspend after a system-wide transition into the working
> state. PM core determines that the driver's "noirq" and "early" resume
> callbacks should be skipped or not with dev_pm_skip_resume() function by
> checking power.may_skip_resume variable.
> 
> power.must_resume variable is getting set to false in __device_suspend()
> function without checking device's DPM_FLAG_MAY_SKIP_RESUME settings.
> In problematic scenario, where all the devices in the suspend_late
> stage are successful and some device can fail to suspend in
> suspend_noirq phase. So some devices successfully suspended in suspend_late
> stage are not getting chance to execute __device_suspend_noirq()
> to set dev->power.must_resume variable to true and not getting
> resumed in early_resume phase.
> 
> Add a check for device's DPM_FLAG_MAY_SKIP_RESUME flag before
> setting power.must_resume variable in __device_suspend function.
> 
> Fixes: 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the resume phase")
> Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
> ---
>  V3 -> V4: Remove dev->power.usage_count variable check
>  V2 -> V3: Format issues patch posting
>  V1 -> V2: Fixed indentation and commit text to include scenario
>  drivers/base/power/main.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index d568772..50e8ea3 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1642,7 +1642,10 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
>  	}
>  
>  	dev->power.may_skip_resume = true;
> -	dev->power.must_resume = false;
> +	if (dev_pm_test_driver_flags(dev, DPM_FLAG_MAY_SKIP_RESUME))
> +		dev->power.must_resume = false;
> +	else
> +		dev->power.must_resume = true;
>  
>  	dpm_watchdog_set(&wd, dev);
>  	device_lock(dev);

Seems sane, Rafael, any comments?

thanks,

greg k-h