linux-kernel - Re: [PATCH] USB: OHCI/UHCI: Add soft dependencies on ehci

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Message-ID: <98e36c6f-f0ee-40d2-be7f-d2ad9f36de07@rowland.harvard.edu>
Date: Fri, 2 Jan 2026 22:33:46 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Diederik de Haas <diederik@...ow-tech.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Huacai Chen <chenhuacai@...ngson.cn>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Shengwen Xiao <atzlinux@...a.com>,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] USB: OHCI/UHCI: Add soft dependencies on ehci_hcd

On Sat, Jan 03, 2026 at 11:16:59AM +0800, Huacai Chen wrote:
> Thank you for your explanation, so it means there are two methods: The
> old one is EHCI with a companion OHCI; the new one is EHCI with a
> USB-2.0 hub. Right?

Right.

> > > So I guess OHCI/UHCI have an EHCI dependency in order to avoid "new
> > > connection", not only in the PCI case.
> >
> > Do you know of any non-PCI systems that do this?
> Unfortunately, in 2026 there are really "EHCI with a companion OHCI"
> for non-PCI systems, please see
> arch/loongarch/boot/dts/loongson-2k0500.dtsi.

Since these systems don't use PCI, the question I raised earlier still 
needs to be answered: How do they route connections between the ports 
and the two controllers?

There may be some exceptions, but for the most part, the code in 
ehci-hcd was written assuming that only PCI-based controllers will have 
companions.  If you want to make an exception for loongson-2k0500, you 
will need to figure out how to get it to work.

Have you tested any of those systems to see how they behave if a USB-1 
device is already plugged in and running when the ehci-hcd driver gets 
loaded?

Alan Stern