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

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Message-ID: <20250828230558.euvmnbgij46kqkeb@synopsys.com>
Date: Thu, 28 Aug 2025 23:06:02 +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 05/22] usb: dwc3: apple: Do not use host-vbus-glitches
 workaround

On Sat, Aug 23, 2025, Sven Peter wrote:
> On 22.08.25 00:28, Thinh Nguyen wrote:
> > On Thu, Aug 21, 2025, Sven Peter wrote:
> > > From: Janne Grunau <j@...nau.net>
> 
> [...]
> 
> > >   	/*
> > >   	 * 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?
> 
> You're absolutely right, this doesn't make any sense!
> 
> dwc3_power_off_all_roothub_ports uses ioremap which will map the XHCI region
> as Device-nGnRE. That just doesn't work on these machines and actually
> explains the SErrors.
> Resources on these machines generally have the IORESOURCE_MEM_NONPOSTED flag
> set (via the nonposted-mmio dt property) and then use ioremap_np to map them
> using Device-nGnRnE.
> 

Ok. So the failure does not seem to be because the phy hasn't been
initialized yet, but it's because of io mapping.

Did you try to check against IORESOURCE_MEM_NONPOSTED to use ioremap_np
instead? That keeps the logic consistent between different platforms.

BR,
Thinh