linux-kernel - Re: [PATCH RFC 04/22] usb: dwc3: apple: Reset dwc3 during role switches

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Message-ID: <20250828231434.koacer62sx6hyagx@synopsys.com>
Date: Thu, 28 Aug 2025 23:14:35 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Sven Peter <sven@...nel.org>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        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>,
        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 04/22] usb: dwc3: apple: Reset dwc3 during role
 switches

On Sun, Aug 24, 2025, Sven Peter wrote:
> On 22.08.25 01:25, Thinh Nguyen wrote:
> > 
> > > +		(dwc->current_dr_role && ((DWC3_IP_IS(DWC3) ||
> > >   			DWC3_VER_IS_PRIOR(DWC31, 190A)) &&
> > > -			desired_dr_role != DWC3_GCTL_PRTCAP_OTG)) {
> > > +			desired_dr_role != DWC3_GCTL_PRTCAP_OTG))) {
> > >   		reg = dwc3_readl(dwc->regs, DWC3_GCTL);
> > >   		reg |= DWC3_GCTL_CORESOFTRESET;
> > >   		dwc3_writel(dwc->regs, DWC3_GCTL, reg);
> > > @@ -1372,6 +1394,9 @@ static int dwc3_core_init(struct dwc3 *dwc)
> > >   	if (ret)
> > >   		goto err_exit_phy;
> > > +	if (dwc->role_switch_reset_quirk)
> > > +		dwc3_enable_susphy(dwc, true);
> > > +
> > 
> > Why do you need to enable susphy here?
> 
> The only place we actually need it is when we shut down the Type-C PHY due
> some what I assume is some hardware quirk, i.e. just before dwc3_core_exit.

Not really hardware quirk. Some low level phy commands can only be
executed while the phy is in low power.

> 
> The PHY will otherwise not be able to acquire some hardware lock (which they
> call PIPEHANDLER lock in debug strings) to switch from e.g. USB3 PHY to a
> dummy PHY for USB2 only. It then can't shut down cleanly anymore and will
> get stuck in a weird state where the port refuses to work until I reset
> everything.
> Originally it was added because we just undid some commit where susphy
> handling was made unconditional IIRC.
> 
> I'll move this to the glue driver with a comment explaining why it's
> required.
> 
> 

Perhaps this patch can give you some clues:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/dwc3/core.c?id=cc5bfc4e16fc1d1c520cd7bb28646e82b6e69217

BR,
Thinh