linux-kernel - Re: [PATCH v2 03/20] ARM: LPAE: use u32 instead of unsigned long for 32-bit ptes

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Date:	Mon, 15 Nov 2010 09:39:30 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v2 03/20] ARM: LPAE: use u32 instead of unsigned long for
 32-bit ptes

On 14 November 2010 15:14, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Sun, Nov 14, 2010 at 02:13:23PM +0000, Catalin Marinas wrote:
>> On Sunday, November 14, 2010, Catalin Marinas <catalin.marinas@....com> wrote:
>> > On Sunday, November 14, 2010, Russell King - ARM Linux
>> > <linux@....linux.org.uk> wrote:
>> >> On Fri, Nov 12, 2010 at 06:00:23PM +0000, Catalin Marinas wrote:
>> >>> From: Will Deacon <will.deacon@....com>
>> >>>
>> >>> When using 2-level paging, pte_t and pmd_t are typedefs for
>> >>> unsigned long but phys_addr_t is a typedef for u32.
>> >>>
>> >>> This patch uses u32 for the page table entry types when
>> >>> phys_addr_t is not 64-bit, allowing the same conversion
>> >>> specifier to be used for physical addresses and page table
>> >>> entries regardless of LPAE.
>> >>
>> >> However, code which prints the value of page table entries assumes that
>> >> they are unsigned long, and places where we store the raw pte value also
>> >> uses 'unsigned long'.
>> >>
>> >> If we're going to make this change, we need to change more places than
>> >> this patch covers.  grep for pte_val to help find those places.
>> >
>> > Patch 19/20 introduces a common macro for formatting but we should
>> > probably order the patches a bit to avoid problems if anyone is
>> > bisecting  in the middle of the series.
>>
>> Actually not a problem since LPAE is only enabled by the last patch.
>> There may be some compiler warnings without 19/20, I need to check.
>
> There will be compiler warnings because u32 is unsigned int, and we
> print it as %08lx.  Generic code cases pte values to (long long) and
> prints them using %08llx.  We should do the same.

We still need some kind of macro because with LPAE we need %016llx
since the phys address can go to 40-bit and there are some additional
bits in the top word. Unless you'd like to always print 16 characters
even for 32-bit ptes (or if there is some other printk magic I'm not
aware of).

> In any case, this patch on its own introduces new compiler warnings.
> These need to be fixed in this patch, rather than relying on one later
> in the series.

Yes, we'll look into this.

-- 
Catalin
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