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

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Date:	Thu, 10 Jan 2013 19:57:30 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Stephen Warren <swarren@...dotorg.org>,
	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>,
	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 Thu, Jan 10, 2013 at 06:26:55PM +0000, Arnd Bergmann wrote:
> On Thursday 10 January 2013, Thierry Reding wrote:
> > I don't understand how this would help. The encoding is like this:
> > 
> >         [27:24] extended register number
> >         [23:16] bus number
> >         [15:11] device number
> >         [10: 8] function number
> >         [ 7: 0] register number
> > 
> > So it doesn't matter whether I use separate areas per bus or not. As
> > soon as the whole extended configuration space needs to be accessed a
> > whopping 28 bits (256 MiB) are required.
> > 
> > What you propose would work if only regular configuration space is
> > supported. I'm not sure if that's an option.
> 
> I mean something like:
> 
> struct tegra_bus_private {
> 	...
> 	void __iomem *config_space[16];
> };
> 
> 
> void tegra_scan_bus(struct pci_bus *bus)
> {
> 	int i;
> 	struct tegra_bus_private *priv = bus->dev->private;
> 
> 	for (i=0; i<16; i++)
> 		priv->config_space[i] = ioremap(config_space_phys +
> 				 65536 * bus->primary + i * SZ_1M, 65536);
> 
> 	...
> }

Okay, I see. It's a bit kludgy, but I guess so was the I/O map cache.
It'll take some more time to work this out and test, but I'll give it
a shot.

Thierry

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