linux-kernel - Re: [PATCH V6 3/5] PCI: thunder-pem: Allow to probe PEM-specific register range for ACPI case

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Date:   Fri, 23 Sep 2016 12:53:07 +0200
From:   Tomasz Nowicki <tn@...ihalf.com>
To:     Bjorn Helgaas <helgaas@...nel.org>, Duc Dang <dhdang@....com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        David Daney <ddaney@...iumnetworks.com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Rafael Wysocki <rafael@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Sinan Kaya <okaya@...eaurora.org>,
        Jayachandran C <jchandra@...adcom.com>,
        Christopher Covington <cov@...eaurora.org>,
        Robert Richter <robert.richter@...iumnetworks.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Liviu Dudau <Liviu.Dudau@....com>,
        Yijing Wang <wangyijing@...wei.com>,
        Mark Salter <msalter@...hat.com>, linux-pci@...r.kernel.org,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
        Jon Masters <jcm@...hat.com>,
        Andrea Gallo <andrea.gallo@...aro.org>,
        Jeremy Linton <jeremy.linton@....com>,
        Dongdong Liu <liudongdong3@...wei.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        Jeff Hugo <jhugo@...eaurora.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH V6 3/5] PCI: thunder-pem: Allow to probe PEM-specific
 register range for ACPI case

Hi Bjorn,

On 21.09.2016 21:18, Bjorn Helgaas wrote:
> On Wed, Sep 21, 2016 at 11:58:22AM -0700, Duc Dang wrote:
>> On Wed, Sep 21, 2016 at 11:04 AM, Bjorn Helgaas <helgaas@...nel.org> wrote:
>>> On Wed, Sep 21, 2016 at 03:05:49PM +0100, Lorenzo Pieralisi wrote:
>
>>> The existing x86 practice is to use PNP0C02 devices for this purpose,
>>> and I think we should just follow that practice.
>>>
>>> ...
>>>
>>> My point is that the hard-coding should not be buried in a driver
>>> where it's invisible to the rest of the kernel.  If we hard-code it in
>>> a quirk that adds _CRS entries, then the kernel will work just like it
>>> would if the firmware had been correct in the first place.  The
>>> resource will appear in /sys/devices/pnp*/*/resources and /proc/iomem,
>>> and if we ever used _SRS to assign or move ACPI devices, we would know
>>> to avoid the bridge resource.
>>
>> Are you suggesting to add code similar to functions in
>> linux/drivers/pnp/quirks.c to declare/attach the additional resource
>> that the host need to have when the resource is not in MCFG table?
>
> Yes, but what I'm suggesting is actually a little stronger.  This has
> nothing to do with whether a resource is in the MCFG table or not.
>
> I'm suggesting ACPI firmware should always describe the resource.  If the
> firmware is defective and doesn't describe it, we should add a quirk in
> pnp/quirks.c to add a resource for it.
>

Thanks for pointers Bjorn.

ThunderX is the case where we cannot change firmware, also it has no 
PNP0c02 device in tables. So in order to use pnp/quirks.c we would have 
to fabricate PNP0c02 in kernel and then add quirk entry. I am looking 
for the best place to put such emulation code but it seems not trivial.

Thanks,
Tomasz