From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Sat, 9 Feb 2013 12:03:31 +0000
Subject: [PATCH 09/17] ARM: add atag32_to_cpu() function
In-Reply-To: <1360365467-25056-10-git-send-email-ben.dooks@codethink.co.uk>
References: <1360365467-25056-1-git-send-email-ben.dooks@codethink.co.uk>
 <1360365467-25056-10-git-send-email-ben.dooks@codethink.co.uk>
Message-ID: <20130209120331.GC17833@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Feb 08, 2013 at 11:17:39PM +0000, Ben Dooks wrote:
> Add atag32_to_cpu() function to allow code manipulating ATAGs to deal
> with the case where the boot-loader was in little-endian and Linux is
> running big-endian.
...
> +#ifdef CONFIG_CPU_BE8_BOOT_LE
> +#define atag32_to_cpu(x)	le32_to_cpu(x)
> +#else
> +#define atag32_to_cpu(x)	x
> +#endif

Actually, with a LE kernel, le32_to_cpu() ends up being a no-op too.  So
I'm wondering if we should do this a different way...

Also, this will cause sparse to complain - le32_to_cpu() takes a le32
type not a u32 type.

This brings up a whole load of difficulties though: what format are the
ATAGs on older BE hardware - I bet it's CPU-endian format there.  So,
I'm wondering if we should do this:

1. define all tags using a new __atagXX, etc types.
2. always use atagXX_to_cpu() to read these.
3. Implement:

#if defined(CONFIG_ATAG_LE)
typedef __le32 __atag32;
...
#define atag32_to_cpu(x) le32_to_cpu(x)
...
#elif defined(CONFIG_ATAG_BE)
typedef __be32 __atag32;
...
#define atag32_to_cpu(x) be32_to_cpu(x)
...
#elif defined(CONFIG_ATAG_NE)
typedef __u32 __atag32;
...
#define atag32_to_cpu(x) x
...
#endif

and select the appropriate definition.  Obviously, this is a fundamental
configuration just like the overall BE/LE configuration of the kernel.