From: Arnd Bergmann <arnd@arndb.de>
To: Sinan Kaya <okaya@codeaurora.org>
Cc: Tomasz Nowicki <tn@semihalf.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>, bhelgaas@google.com,
        will.deacon@arm.com, catalin.marinas@arm.com, rjw@rjwysocki.net,
        hanjun.guo@linaro.org, jiang.liu@linux.intel.com,
        robert.richter@caviumnetworks.com, Narinder.Dhillon@caviumnetworks.com,
        ddaney@caviumnetworks.com, Liviu.Dudau@arm.com, tglx@linutronix.de,
        wangyijing@huawei.com, Suravee.Suthikulpanit@amd.com,
        msalter@redhat.com, linux-pci@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linaro-acpi@lists.linaro.org
Subject: Re: [PATCH V1 11/11] arm64, pci, acpi: Support for ACPI based PCI hostbridge init
Date: Tue, 03 Nov 2015 16:59:28 +0100
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On Tuesday 03 November 2015 10:10:21 Sinan Kaya wrote:
> 
> I don't see anywhere in the SBSA spec addendum that the PCI 
> configuration space section that unaligned accesses *MUST* be supported.
> 
> If this is required, please have this info added to the spec. I can work 
> with the designers for the next chip.
> 
> Unaligned access on the current hardware returns incomplete values or 
> can cause bus faults. The behavior is undefined.

Unaligned accesses are not allowed, but any PCI compliant device must
support aligned 1, 2 or 4 byte accesses on its configuration space,
though the byte-enable mechanism. In an ECAM host bridge, those are
mapped to load/store accesses from the CPU with the respective width
and natural alignment.

	Arnd
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