linux-kernel - Re: [patch] x86, voyager: fix ioremap

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Date:	Sun, 27 Apr 2008 18:39:24 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] x86, voyager: fix ioremap_nocache()

James Bottomley wrote:
> Here's another piece of the x86 API that's designed to be cached.  The
> dma_declare_coherent_memory() usually represents behind bridge memory
> that's fully participatory in the coherence model.
> 
> Making it uncached damages the utility of this memory because doing
> cacheline sized burst cycles when needed to it is far faster than
> individual byte/word/quad writes.
> 
> Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>
> 
> ---
> 
> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> index 388b113..df83ffd 100644
> --- a/arch/x86/kernel/pci-dma.c
> +++ b/arch/x86/kernel/pci-dma.c
> @@ -214,7 +214,7 @@ int dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
>  
>  	/* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN */
>  
> -	mem_base = ioremap(bus_addr, size);
> +	mem_base = ioremap_cache(bus_addr, size);
>  	if (!mem_base)
>  		goto out;

Surely the change in semantics will find other places to creep out like 
this?

I would rather change drivers to use ioremap_nocache(), and leave the 
API as-is.

Isn't there Yet More Breakage in lib/iomap.c, given these new semantics?

         if (flags & IORESOURCE_MEM) {
                 if (flags & IORESOURCE_CACHEABLE)
                         return ioremap(start, len);
                 return ioremap_nocache(start, len);
         }

Any driver using pci_iomap() (libata, and others) is affected.

I disagree with this semantics change.  A number of code places _and 
drivers_ GET IT RIGHT, and these are all broken now?

	Jeff



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