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 09:31:11 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 5/13/2020 9:27 AM, Greg Kroah-Hartman 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");
> 
> 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.

I also suggested that device links may help, though I am not sure. What
do you suggest to be done?
-- 
Florian