linux-kernel - Re: [PATCH] pci: introduce users of ioremap

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Message-ID: <20080929171049.GA14409@colo.lackof.org>
Date:	Mon, 29 Sep 2008 11:10:49 -0600
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Grant Grundler <grundler@...isc-linux.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: introduce users of ioremap_pcibar()

On Mon, Sep 29, 2008 at 06:42:20AM -0700, Arjan van de Ven wrote:
...
> > This patch changes that behavior of the device driver so it uses
> > uncacheable instead of cacheable mappings.  This is the only thing
> > I'm uncertain about for this patch.
> 
> ioremap() also is uncachable today.

Ok...it was using cacheable mapping on ia64 until this commit in 2007:
    http://www.gelato.unsw.edu.au/archives/linux-ia64/0703/20211.html

I stopped paying close attention  on ia64 in 2006 for the most part.
It's always been uncacheable on parisc.

After finding willy's patch (March 2006) on lwn.net, I remember the
discussion around changing the behavior of ioremap() to be uncached:
    http://lwn.net/Articles/178084/

And I have to agree with willy/alan, pci_iomap() is already doing this.

However, pci_iomap() isn't quite right either:
        if (flags & IORESOURCE_MEM) {
                if (flags & IORESOURCE_CACHEABLE)
                        return ioremap(start, len);
                return ioremap_nocache(start, len);
        }

I expect it needs to use ioremap_cache() instead of ioremap().
One line patch below fixes that. Build-tested on x86 only.

Signed-off-by: Grant Grundler <grundler@...isc-linux.org>

> > And I have a second issue less important issue.
> > What is the result of ioremap_pcibar(pci, 1) when BAR0 is a 64-bit
> > bar? Given the name, I expect to call "ioremap_pcibar(pci,2)" to get
> > the desired result.  Maybe just document how to handle this correctly
> > in Documentation/pci.txt would be sufficient.
> 
> we should detect this and DTRT inside the implementation, not in the
> drivers.

pci_iomap() is already doing this. See lib/iomap.c:pci_iomap().

thanks,
grant


diff --git a/lib/iomap.c b/lib/iomap.c
index d322293..5565cf9 100644
--- a/lib/iomap.c
+++ b/lib/iomap.c
@@ -267,7 +267,7 @@ void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen)
 		return ioport_map(start, len);
 	if (flags & IORESOURCE_MEM) {
 		if (flags & IORESOURCE_CACHEABLE)
-			return ioremap(start, len);
+			return ioremap_cache(start, len);
 		return ioremap_nocache(start, len);
 	}
 	/* What? */
--
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