linux-kernel - Re: [PATCH 6/9] drivers: add Contiguous Memory Allocator

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Date:	Sun, 16 Oct 2011 11:08:21 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ankita Garg <ankita@...ibm.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Mel Gorman <mel@....ul.ie>, Arnd Bergmann <arnd@...db.de>,
	Jesse Barker <jesse.barker@...aro.org>,
	Jonathan Corbet <corbet@....net>,
	Shariq Hasnain <shariq.hasnain@...aro.org>,
	Chunsang Jeong <chunsang.jeong@...aro.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: Re: [PATCH 6/9] drivers: add Contiguous Memory Allocator

On Fri, Oct 14, 2011 at 04:57:30PM -0700, Andrew Morton wrote:
> On Thu, 06 Oct 2011 15:54:46 +0200
> Marek Szyprowski <m.szyprowski@...sung.com> wrote:
> > +#ifdef phys_to_pfn
> > +/* nothing to do */
> > +#elif defined __phys_to_pfn
> > +#  define phys_to_pfn __phys_to_pfn
> > +#elif defined __va
> > +#  define phys_to_pfn(x) page_to_pfn(virt_to_page(__va(x)))
> > +#else
> > +#  error phys_to_pfn implementation needed
> > +#endif
> 
> Yikes!
> 
> This hackery should not be here, please.  If we need a phys_to_pfn()
> then let's write a proper one which lives in core MM and arch, then get
> it suitably reviewed and integrated and then maintained.

Another question is whether we have any arch where PFN != PHYS >> PAGE_SHIFT?
We've used __phys_to_pfn() to implement that on ARM (with a corresponding
__pfn_to_phys()).  Catalin recently added a cast to __phys_to_pfn() for
LPAE, which I don't think is required:

-#define        __phys_to_pfn(paddr)    ((paddr) >> PAGE_SHIFT)
+#define        __phys_to_pfn(paddr)    ((unsigned long)((paddr) >> PAGE_SHIFT))

since a phys_addr_t >> PAGE_SHIFT will be silently truncated if the passed
in physical address was 64-bit anyway.  (Note: we don't support > 32-bit
PFNs).

So, I'd suggest CMA should just use PFN_DOWN() and be done with it.
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