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

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Message-ID: <c052860b-c239-43a6-b05d-c8495bc1c731@kernel.org>
Date: Sat, 23 Aug 2025 13:42:09 +0200
From: Sven Peter <sven@...nel.org>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
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>,
 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 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.


Best,


Sven