Subject: N900 v3.19-rc5 arm atags_to_fdt.c is broken

From: [email-masked] (Pavel Machek)
Date: Mon, 26 Jan 2015 22:48:21 +0100

Hi!

> > > $ du -b arch/arm/boot/dts/omap3-n900.dtb 
> > > 70212   arch/arm/boot/dts/omap3-n900.dtb
> > > 
> > > $ echo $((0x10000))
> > > 65536
> > > 
> > > I would say, problem is because omap3-n900 binary DT is too large
> 
> I agree.
> 
> > OK if that's the case, then your patch makes sense to me. It also
> > seems we can have the temporary stack be larger than the initial
> > stack just for atags_to_fdt.
> 
> The stack size isn't the issue, but rather its location.  We need to 
> position it away from the DT data.  The DT size is known and we could 
> use that, plus some room for the insertion of new data coming from the
> ATAG conversion.
> 
> Something like the following would be a more robust solution:
> 
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 68be901759..89718de9dd 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -263,16 +263,37 @@ restart:	adr	r0, LC0
>  		 * OK... Let's do some funky business here.
>  		 * If we do have a DTB appended to zImage, and we do have
>  		 * an ATAG list around, we want the later to be translated
> -		 * and folded into the former here.  To be on the safe side,
> -		 * let's temporarily move  the stack away into the malloc
> -		 * area.  No GOT fixup has occurred yet, but none of the
> -		 * code we're about to call uses any global variable.
> +		 * and folded into the former here. No GOT fixup has occurred
> +		 * yet, but none of the code we're about to call uses any
> +		 * global variable.
>  		*/
> -		add	sp, sp, #0x10000
> +
> +		/* Get the initial DTB size */
> +		ldr	r5, [r6, #4]
> +#ifndef __ARMEB__
> +		/* convert to little endian */
> +		eor	r1, r5, r5, ror #16
> +		bic	r1, r1, #0x00ff0000
> +		mov	r5, r5, ror #8
> +		eor	r5, r5, r1, lsr #8
> +#endif
> +		/* 50% DTB growth should be good enough */
> +		add	r5, r5, r5, lsr #1
> +		/* preserve 64-bit alignment */
> +		add	r5, r5, #7
> +		bic	r5, r5, #7
> +		/* clamp to 32KB min and 1MB max */
> +		movs	r1, r5, lsr #15
> +		moveq	r5, #(1 << 15)
> +		movs	r1, r5, lsr #20
> +		movne	r5, #(1 << 20)

Dunno. Would it be easier/simpler to just use 1MB, always? Do we
support machines with <16MB RAM?

Best regards,

-- 
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