linux-kernel - Re: [PATCH V6 4/5] PCI: thunder: Enable ACPI PCI controller for ThunderX pass2.x silicon version

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Message-ID: <c7636112-b080-9101-e504-8a4acd19c96a@semihalf.com>
Date:   Wed, 21 Sep 2016 10:05:49 +0200
From:   Tomasz Nowicki <tn@...ihalf.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     will.deacon@....com, catalin.marinas@....com, rafael@...nel.org,
        Lorenzo.Pieralisi@....com, arnd@...db.de, hanjun.guo@...aro.org,
        okaya@...eaurora.org, jchandra@...adcom.com, cov@...eaurora.org,
        dhdang@....com, ard.biesheuvel@...aro.org,
        robert.richter@...iumnetworks.com, mw@...ihalf.com,
        Liviu.Dudau@....com, ddaney@...iumnetworks.com,
        wangyijing@...wei.com, msalter@...hat.com,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linaro-acpi@...ts.linaro.org, jcm@...hat.com,
        andrea.gallo@...aro.org, jeremy.linton@....com,
        liudongdong3@...wei.com, gabriele.paoloni@...wei.com,
        jhugo@...eaurora.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 4/5] PCI: thunder: Enable ACPI PCI controller for
 ThunderX pass2.x silicon version

On 20.09.2016 15:08, Bjorn Helgaas wrote:
> On Tue, Sep 20, 2016 at 09:06:23AM +0200, Tomasz Nowicki wrote:
>> On 19.09.2016 17:45, Bjorn Helgaas wrote:
>>> On Fri, Sep 09, 2016 at 09:24:06PM +0200, Tomasz Nowicki wrote:
>>>> ThunderX PCIe controller to off-chip devices (so-called PEM) is not fully
>>>> compliant with ECAM standard. It uses non-standard configuration space
>>>> accessors (see pci_thunder_pem_ops) and custom configuration space granulation
>>>> (see bus_shift = 24). In order to access configuration space and
>>>> probe PEM as ACPI based PCI host controller we need to add MCFG quirk
>>>> infrastructure. This involves:
>>>> 1. Export PEM pci_thunder_pem_ops structure so it is visible to MCFG quirk
>>>>   code.
>>>> 2. New quirk entries for each PEM segment. Each contains platform IDs,
>>>>   mentioned pci_thunder_pem_ops and CFG resources.
>>>>
>>>> Quirk is considered for ThunderX silicon pass2.x only which is identified
>>>> via MCFG revision 1.
>>>
>>> Is it really the case that silicon pass2.x has MCFG revision 1, and
>>> silicon pass1.x has MCFG revision 2?  That just seems backwards.
>>
>> It is weird but silicon pass2.x is more common and it had MCFG
>> revision 1 from the beginning. Unless it is allowed to use MCFG
>> revision 0 ? Then we could use MCFG revision 0 for pass1.x
>
> There's no reason to avoid revision 0.  The question is really what
> firmware is already in the field.  We need to accommodate that.  We don't
> want a situation where kernel version X only works with firmware version Y,
> but kernel version X+1 only works with firmware version Y+1.

Yes I agree. We have already deployed the firmware where:
pass2.x has MCFG revision 1
pass1.x has MCFG revision 2
so we need to stick to this.

Thanks,
Tomasz