linux-kernel - Re: [PATCH RFC 05/22] usb: dwc3: apple: Do not use host-vbus-glitches workaround

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Message-ID: <20250821222842.fqrxjp56czc7ubok@synopsys.com>
Date: Thu, 21 Aug 2025 22:28:46 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Sven Peter <sven@...nel.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, Felipe Balbi <balbi@...nel.org>,
        Janne Grunau <j@...nau.net>, Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Neal Gompa <neal@...pa.dev>, Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "asahi@...ts.linux.dev" <asahi@...ts.linux.dev>,
        "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH RFC 05/22] usb: dwc3: apple: Do not use host-vbus-glitches
 workaround

On Thu, Aug 21, 2025, Sven Peter wrote:
> From: Janne Grunau <j@...nau.net>
> 
> It results in SErrors during init presumedly because MMIO accesses fail
> while certain parts are shutdown.
> 
> Signed-off-by: Janne Grunau <j@...nau.net>
> Signed-off-by: Sven Peter <sven@...nel.org>
> ---
>  drivers/usb/dwc3/core.c | 1 +
>  drivers/usb/dwc3/core.h | 2 ++
>  drivers/usb/dwc3/host.c | 5 ++++-
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 26aa507a738f001409a97ef563c6561433a1cac5..8d2dc7fa18114102cc8893c4ca0e745e16f30754 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -2273,6 +2273,7 @@ int dwc3_core_probe(const struct dwc3_probe_data *data)
>  
>  			dwc->dr_mode = USB_DR_MODE_OTG;
>  			dwc->role_switch_reset_quirk = true;
> +			dwc->no_early_roothub_poweroff = true;
>  		}
>  	}
>  
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index 38f32f2a6193c1b2662ab4f38f4d20cf4b0e198d..3c3a36ec37345b2f9e71444ba3b90b52dbd24443 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -1155,6 +1155,7 @@ struct dwc3_scratchpad_array {
>   * @susphy_state: state of DWC3_GUSB2PHYCFG_SUSPHY + DWC3_GUSB3PIPECTL_SUSPHY
>   *		  before PM suspend.
>   * @role_switch_reset_quirk: set to force reinitialization after any role switch
> + * @no_early_roothub_poweroff: set to skip early root hub port power off
>   * @imod_interval: set the interrupt moderation interval in 250ns
>   *			increments or 0 to disable.
>   * @max_cfg_eps: current max number of IN eps used across all USB configs.
> @@ -1394,6 +1395,7 @@ struct dwc3 {
>  	unsigned		susphy_state:1;
>  
>  	unsigned		role_switch_reset_quirk:1;
> +	unsigned		no_early_roothub_poweroff:1;
>  
>  	u16			imod_interval;
>  
> diff --git a/drivers/usb/dwc3/host.c b/drivers/usb/dwc3/host.c
> index f7a71e6f9d80aca632f1f970d900a3de8a76f0a7..f7c3a0fc5fe258705311f89c1ba11ff599c01afe 100644
> --- a/drivers/usb/dwc3/host.c
> +++ b/drivers/usb/dwc3/host.c
> @@ -134,8 +134,11 @@ int dwc3_host_init(struct dwc3 *dwc)
>  	/*
>  	 * Some platforms need to power off all Root hub ports immediately after DWC3 set to host
>  	 * mode to avoid VBUS glitch happen when xhci get reset later.
> +	 * On Apple platforms we must not touch any MMIO yet because dwc3
> +	 * will not work correctly before its PHY has been initialized.

This doesn't make sense, the phy should've been initialized by this
point. We already access MMIO before this. Even your [PATCH RFC 7/22]
attempts to access MMIO before this, yet accessing here causes problem.
Do we know when the phy get initialized then?

BR,
Thinh

>  	 */
> -	dwc3_power_off_all_roothub_ports(dwc);
> +	if (!dwc->no_early_roothub_poweroff)
> +		dwc3_power_off_all_roothub_ports(dwc);
>  
>  	irq = dwc3_host_get_irq(dwc);
>  	if (irq < 0)
> 
> -- 
> 2.34.1
> 
>