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:   Wed, 21 Sep 2016 14:18:45 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Duc Dang <dhdang@....com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Tomasz Nowicki <tn@...ihalf.com>,
        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

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.

Bjorn