From: Arnd Bergmann <arnd@arndb.de>
To: Tomasz Nowicki <tn@semihalf.com>
Cc: Jayachandran C <jchandra@broadcom.com>,
        linux-arm-kernel@lists.infradead.org,
        Bjorn Helgaas <helgaas@kernel.org>, Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>, rafael@kernel.org,
        Hanjun Guo <hanjun.guo@linaro.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Sinan Kaya <okaya@codeaurora.org>, jiang.liu@linux.intel.com,
        Jon Masters <jcm@redhat.com>, linaro-acpi@lists.linaro.org,
        linux-pci@vger.kernel.org, Liviu.Dudau@arm.com,
        David Daney <ddaney@caviumnetworks.com>, linux-kernel@vger.kernel.org,
        linux-acpi@vger.kernel.org, robert.richter@caviumnetworks.com,
        Suravee.Suthikulpanit@amd.com, msalter@redhat.com,
        Wangyijing <wangyijing@huawei.com>, Marcin Wojtas <mw@semihalf.com>
Subject: Re: [PATCH V6 08/13] PCI: generic, thunder: update to use generic ECAM API
Date: Thu, 21 Apr 2016 11:36:53 +0200
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On Thursday 21 April 2016 11:28:15 Tomasz Nowicki wrote:
> On 19.04.2016 15:06, Arnd Bergmann wrote:
> > On Monday 18 April 2016 21:31:54 Tomasz Nowicki wrote:
> >>
> >> Basically the whole content of pci-thunder-ecam.c and pci-thunder-pem.c.
> >>
> >> pci-thunder-ecam.c contains config space accessors. Similar for
> >> pci-thunder-pem.c but it also has extra init call (it is now called
> >> thunder_pem_init) which finds and maps related registers.
> >
> > They seem to do much more than just override the accessors, they actually
> > change the contents of the config space as well. Is that really necessary
> > on ACPI based systems as well?
> 
> Yes, the pci-thunder-ecam.c accessors are meant to emulate config space 
> capabilities. They are necessary to synthesize EA capabilities (fixed 
> PCI BARs), it wont work without this, for ACPI boot as well.

Why is that? I thought the BARs never get reassigned when using ACPI,
so I'm surprised it's actually needed. Maybe I misunderstood what
you mean by fixed PCI BARs.

> > Another idea: how about moving all of this logic into ACPI and calling
> > some AML method to access the config space if the devices are that
> > far out of spec.
> 
> Do you mean Linux specific way to call non-standard config space 
> accessors? Then non-standard accessors are going to AML methods which 
> are called from common code which handles quirks via unified API ?

What I really meant was a standardized way to do handle hardware that
is in some way or another not compliant with PNP0A08: We could have
a different hardware ID for this and let all the first-generation
ARM servers and also anything else using ACPI with nonstandard PCI
use the same method across operating systems.

	Arnd