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 08:28:51 -0700
From:   Florian Fainelli <florian.fainelli@...adcom.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Cooper <alcooperx@...il.com>, linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        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>
Subject: Re: [PATCH v10 1/5] usb: xhci: Change the XHCI link order in the
 Makefile



On 5/13/2020 8:26 AM, Andy Shevchenko wrote:
> 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");
> 
> JFYI: not all user space support this (alas, but that's current state of
> affairs), OTOH I don't really care about those which do not support it
> (Busybox).

I know that Gentoo's initramfs tool does not support it, however given
there are no symbols being cross referenced, I am not sure how to best
support this other than using these hints, and possibly making use of
device links too?
-- 
Florian