linux-kernel - Re: [PATCH 05/14] lib: Add I/O map cache implementation

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Message-ID: <50EDF95F.4070209@wwwdotorg.org>
Date:	Wed, 09 Jan 2013 16:12:31 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Thierry Reding <thierry.reding@...onic-design.de>,
	linux-tegra@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Andrew Murray <andrew.murray@....com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 05/14] lib: Add I/O map cache implementation

On 01/09/2013 03:10 PM, Arnd Bergmann wrote:
> On Wednesday 09 January 2013, Thierry Reding wrote:
>> What happens on Tegra is that we need to map 256 MiB of physical memory
>> to access all the PCIe extended configuration space. However, ioremap()
>> on such a large region fails if not enough vmalloc() space is available.
>>
>> This was observed when somebody tested this on CardHu which has a 1 GiB
>> of RAM and therefore remapping the full 256 MiB fails.
...
> Have you checked if the hardware supports an alternative config
> space access mechanism that does not depend on a huge address range?
> A lot of them provide an index/data register pair somewhere, as the
> original PC implementation did.

That would be nice, but I've talked to the HW engineers, and there's no
indication that any alternative mechanism exists.
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