linux-kernel - Re: [PATCH v2] usb: dwc3: core: Avoid redundant system suspend/resume callbacks

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Message-ID: <20250312230216.l2e55tb5l6e4xyt2@synopsys.com>
Date: Wed, 12 Mar 2025 23:02:20 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Roy Luo <royluo@...gle.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: core: Avoid redundant system suspend/resume
 callbacks

On Wed, Mar 12, 2025, Roy Luo wrote:
> dwc3 device suspend/resume callbacks were being triggered during system
> suspend and resume even if the device was already runtime-suspended.
> This is redundant for device mode because the suspend and resume routines
> are essentially identical for system PM and runtime PM.
> 
> To prevent these unnecessary callbacks, indicate to the PM core that it
> can safely leave the device in runtime suspend if it's already
> runtime-suspended in device mode by returning a positive value in
> prepare() callback. This optimization only applies to devices without
> pinctrl, as pinctrl has distinct logic tied to system suspend/resume.
> 
> Signed-off-by: Roy Luo <royluo@...gle.com>
> ---
> Changes in v2:
> - leave the pinctrl logic untouched, apply the optimization only when
>   pinctrl isn't being used.
> ---
>  drivers/usb/dwc3/core.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 66a08b527165..02cdd0727a5e 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -26,6 +26,7 @@
>  #include <linux/of_graph.h>
>  #include <linux/acpi.h>
>  #include <linux/pinctrl/consumer.h>
> +#include <linux/pinctrl/devinfo.h>
>  #include <linux/reset.h>
>  #include <linux/bitfield.h>
>  
> @@ -2658,14 +2659,31 @@ static void dwc3_complete(struct device *dev)
>  		dwc3_writel(dwc->regs, DWC3_GUCTL3, reg);
>  	}
>  }
> +
> +static int dwc3_prepare(struct device *dev)
> +{
> +	struct dwc3	*dwc = dev_get_drvdata(dev);
> +
> +	/*
> +	 * Indicate to the PM core that it may safely leave the device in
> +	 * runtime suspend if runtime-suspended already in device mode.
> +	 */
> +	if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_DEVICE &&
> +	    pm_runtime_suspended(dev) &&
> +	    !dev_pinctrl(dev))
> +		return 1;
> +
> +	return 0;
> +}
>  #else
>  #define dwc3_complete NULL
> +#define dwc3_prepare NULL
>  #endif /* CONFIG_PM_SLEEP */
>  
>  static const struct dev_pm_ops dwc3_dev_pm_ops = {
>  	SET_SYSTEM_SLEEP_PM_OPS(dwc3_suspend, dwc3_resume)
>  	.complete = dwc3_complete,
> -
> +	.prepare = dwc3_prepare,
>  	/*
>  	 * Runtime suspend halts the controller on disconnection. It relies on
>  	 * platforms with custom connection notification to start the controller
> 
> base-commit: 0fed89a961ea851945d23cc35beb59d6e56c0964
> -- 
> 2.49.0.rc1.451.g8f38331e32-goog
> 

Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>

Thanks,
Thinh