Subject: [PATCH 1/3] arm64: merge __enable_mmu and __turn_mmu_on

From: [email-masked] (Mark Rutland)
Date: Tue, 17 Mar 2015 13:51:47 +0000

On Tue, Mar 17, 2015 at 10:11:12AM +0000, Ard Biesheuvel wrote:
> Enabling of the MMU is split into two functions, with an align and
> a branch in the middle. On arm64, the entire kernel Image is ID mapped
> so this is really not necessary, and we can just merge it into a
> single function.
> 
> Signed-off-by: Ard Biesheuvel <[email-masked]>
> ---
>  arch/arm64/kernel/head.S | 30 ++++++++----------------------
>  1 file changed, 8 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 65c7de889c8c..fb912314d5e1 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -615,8 +615,13 @@ ENDPROC(__secondary_switched)
>  #endif	/* CONFIG_SMP */
>  
>  /*
> - * Setup common bits before finally enabling the MMU. Essentially this is just
> - * loading the page table pointer and vector base registers.
> + * Enable the MMU. This completely changes the structure of the visible memory
> + * space. You will not be able to trace execution through this.
> + *
> + *  x0  = system control register
> + *  x27 = *virtual* address to jump to upon completion
> + *
> + * other registers depend on the function called upon completion
>   *
>   * On entry to this code, x0 must contain the SCTLR_EL1 value for turning on
>   * the MMU.

Minor nit: it's a bit redundant to have both comments regarding the
sctlr_el1.

I'd recommed we drop/fold the 2nd comment into the first like:

	x0  = SCTLR_EL1 value for turning on the MMU.

Otherwise, this looks good.

Reviewed-by: Mark Rutland <[email-masked]>

Mark.

> @@ -627,29 +632,10 @@ __enable_mmu:
>  	msr	ttbr0_el1, x25			// load TTBR0
>  	msr	ttbr1_el1, x26			// load TTBR1
>  	isb
> -	b	__turn_mmu_on
> -ENDPROC(__enable_mmu)
> -
> -/*
> - * Enable the MMU. This completely changes the structure of the visible memory
> - * space. You will not be able to trace execution through this.
> - *
> - *  x0  = system control register
> - *  x27 = *virtual* address to jump to upon completion
> - *
> - * other registers depend on the function called upon completion
> - *
> - * We align the entire function to the smallest power of two larger than it to
> - * ensure it fits within a single block map entry. Otherwise were PHYS_OFFSET
> - * close to the end of a 512MB or 1GB block we might require an additional
> - * table to map the entire function.
> - */
> -	.align	4
> -__turn_mmu_on:
>  	msr	sctlr_el1, x0
>  	isb
>  	br	x27
> -ENDPROC(__turn_mmu_on)
> +ENDPROC(__enable_mmu)
>  
>  /*
>   * Calculate the start of physical memory.
> -- 
> 1.8.3.2
> 
>