linux-kernel - Re: [PATCH v10 1/5] usb: xhci: Change the XHCI link order in the Makefile

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Date:   Wed, 13 May 2020 18:27:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Al Cooper <alcooperx@...il.com>, linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-usb@...r.kernel.org, Mathias Nyman <mathias.nyman@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v10 1/5] usb: xhci: Change the XHCI link order in the
 Makefile

On Wed, May 13, 2020 at 08:08:07AM -0700, Florian Fainelli wrote:
> 
> 
> On 5/13/2020 5:26 AM, Greg Kroah-Hartman wrote:
> > On Tue, May 12, 2020 at 11:00:15AM -0400, Al Cooper wrote:
> >> Some BRCMSTB USB chips have an XHCI, EHCI and OHCI controller
> >> on the same port where XHCI handles 3.0 devices, EHCI handles 2.0
> >> devices and OHCI handles <2.0 devices. Currently the Makefile
> >> has XHCI linking at the bottom which will result in the XHIC driver
> >> initalizing after the EHCI and OHCI drivers and any installed 3.0
> >> device will be seen as a 2.0 device. Moving the XHCI linking
> >> above the EHCI and OHCI linking fixes the issue.
> > 
> > What happens if all of these are modules and they are loaded in a
> > different order?  This makefile change will not help with that, you need
> > to have logic in the code in order to properly coordinate this type of
> > mess, sorry.
> 
> I believe we should be using module soft dependencies to instruct the
> module loaders to load the modules in the correct order, so something
> like this would do (not tested) for xhci-plat-hcd.c:
> 
> MODULE_SOFTDEP("post: ehci-hcd ohci-hcd");
> 
> and I am not sure whether we need to add the opposite for ehci-hcd and
> ohci-hcd:
> 
> MODULE_SOFTDEP("pre: xhci-plat-hcd");

That's a nice start, but what happens if that isn't honored?  This
really needs to work properly for any order as you never can guarantee
module/driver loading order in a system of modules.

thanks,

greg k-h