linux-kernel - Re: [PATCH] usb: dwc2: drd: fix clock gating on USB role switch

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Message-ID: <a2ea1fa0-645d-2a16-f396-797e5b96fd45@omp.ru>
Date: Tue, 3 Sep 2024 16:20:26 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Tomas Marek <tomas.marek@...est.cz>, <hminas@...opsys.com>,
	<gregkh@...uxfoundation.org>
CC: <Arthur.Petrosyan@...opsys.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <oleg.karfich@...o.com>
Subject: Re: [PATCH] usb: dwc2: drd: fix clock gating on USB role switch

On 9/3/24 12:41 PM, Tomas Marek wrote:

> The dwc2_handle_usb_suspend_intr() function disables gadget clocks in USB
> peripheral mode when no other power-down mode is available (introduced by
> commit 0112b7ce68ea ("usb: dwc2: Update dwc2_handle_usb_suspend_intr function.")).
> However, the dwc2_drd_role_sw_set() USB role update handler attempts to
> read DWC2 registers if the USB role has changed while the USB is in suspend
> mode (when the clocks are gated). This causes the system to hang.
> 
> Release gadget clocks before handling the USB role update.
> 
> Fixes: 0112b7ce68ea ("usb: dwc2: Update dwc2_handle_usb_suspend_intr function.")
> 
> Signed-off-by: Tomas Marek <tomas.marek@...est.cz>
> ---
>  drivers/usb/dwc2/drd.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/usb/dwc2/drd.c b/drivers/usb/dwc2/drd.c
> index a8605b02115b..ccb33cd1f04b 100644
> --- a/drivers/usb/dwc2/drd.c
> +++ b/drivers/usb/dwc2/drd.c
> @@ -127,6 +127,18 @@ static int dwc2_drd_role_sw_set(struct usb_role_switch *sw, enum usb_role role)
>  			role = USB_ROLE_DEVICE;
>  	}
>  
> +#if IS_ENABLED(CONFIG_USB_DWC2_PERIPHERAL) || \
> +	IS_ENABLED(CONFIG_USB_DWC2_DUAL_ROLE)
> +	if (dwc2_is_device_mode(hsotg)) {

   Why not avoid #ifdef by doing e.g.:

	if ((IS_ENABLED(CONFIG_USB_DWC2_PERIPHERAL) || \
	     IS_ENABLED(CONFIG_USB_DWC2_DUAL_ROLE) &&
	     dwc2_is_device_mode(hsotg)) {

> +		if (hsotg->lx_state == DWC2_L2) {
> +			if (hsotg->params.power_down ==
> +			    DWC2_POWER_DOWN_PARAM_NONE && hsotg->bus_suspended &&
> +			    !hsotg->params.no_clock_gating)

   Well, these *if*s are mergeable too... :-)

> +				dwc2_gadget_exit_clock_gating(hsotg, 0);
> +		}
> +	}
> +#endif
> +
[...]

MBR, Sergey