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

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Message-ID: <CAAhV-H5GdkMg-uzMpDQPGLs+gWNAy6ZOH33VoLqnNyWbRenNDw@mail.gmail.com>
Date: Fri, 2 Jan 2026 10:36:35 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Alan Stern <stern@...land.harvard.edu>
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 Wed, Dec 31, 2025 at 11:21 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Wed, Dec 31, 2025 at 05:38:05PM +0800, Huacai Chen wrote:
> > From your long explanation I think the order is still important. "New
> > connection" may be harmless for USB keyboard/mouse, but really
> > unacceptable for USB storage.
> >
> > If we revert 05c92da0c524 and 9beeee6584b9, the real problem doesn't
> > disappear. Then we go back to pre-2008 to rely on distributions
> > providing a correct modprobe.conf?
>
> The warning message in 9beeee6584b9 was written a long time ago; back
> then I didn't realize that the real dependency was between the -pci
> drivers rather than the -hcd ones (and I wasn't aware of softdeps).  The
> soft dependency in 05c92da0c524 is between the -pci drivers, so it is
> correct.
>
> To put it another way, on PCI-based systems it is not a problem if the
> modules are loaded in this order: uhci-hcd, ohci-hcd, ehci-hcd,
> ehci-pci, ohci-pci, uhci-pci.  Even though the warning message would be
> logged, the message would be wrong.
Correct me if I'm wrong.

I found XHCI is compatible with USB1.0/2.0 devices, but EHCI isn't
compatible with USB1.0. Instead, EHCI usually has an OHCI together,
this is not only in the PCI case.

So I guess OHCI/UHCI have an EHCI dependency in order to avoid "new
connection", not only in the PCI case.


Huacai

>
> On the whole, I think the best approach is to revert 9beeee6584b9's
> warning message while keeping 05c92da0c524's softdeps.  Greg might not
> approve of soft dependencies between modules in general, but in this
> case I believe it is appropriate.
>
> And so your patch really is not needed, as far as I can tell.  While it
> might in theory help some peculiar platform-dependent scenario, I'm
> not aware of any platforms like that.
>
> Alan Stern