Re: [PATCH v2 26/34] ARM: mmu32: Assume MMU is on

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 17.05.23 11:03, Sascha Hauer wrote:
> As we now always enable the MMU during early initialization we can
> safely assume that the MMU is already enabled in __mmu_init() and
> drop the code path which enables the MMU.
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>  arch/arm/cpu/mmu_32.c | 47 +++++++++----------------------------------
>  1 file changed, 10 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/arm/cpu/mmu_32.c b/arch/arm/cpu/mmu_32.c
> index bef4a01670..7cd732580e 100644
> --- a/arch/arm/cpu/mmu_32.c
> +++ b/arch/arm/cpu/mmu_32.c
> @@ -24,12 +24,6 @@
>  #define PTRS_PER_PTE		(PGDIR_SIZE / PAGE_SIZE)
>  #define ARCH_MAP_WRITECOMBINE	((unsigned)-1)
>  
> -/*
> - * We have a 4GiB address space split into 1MiB sections, with each
> - * section header taking 4 bytes
> - */
> -#define ARM_TTB_SIZE	(SZ_4G / SZ_1M * sizeof(u32))
> -
>  static uint32_t *ttb;
>  
>  /*
> @@ -457,38 +451,19 @@ void __mmu_init(bool mmu_on)
>  		pte_flags_uncached = PTE_FLAGS_UNCACHED_V4;
>  	}
>  
> -	if (mmu_on) {
> +	/* Clear unpredictable bits [13:0] */
> +	ttb = (uint32_t *)(get_ttbr() & ~0x3fff);
> +
> +	if (!request_sdram_region("ttb", (unsigned long)ttb, SZ_16K))
>  		/*
> -		 * Early MMU code has already enabled the MMU. We assume a
> -		 * flat 1:1 section mapping in this case.
> +		 * This can mean that:
> +		 * - the early MMU code has put the ttb into a place
> +		 *   which we don't have inside our available memory
> +		 * - Somebody else has occupied the ttb region which means
> +		 *   the ttb will get corrupted.
>  		 */
> -		/* Clear unpredictable bits [13:0] */
> -		ttb = (uint32_t *)(get_ttbr() & ~0x3fff);
> -
> -		if (!request_sdram_region("ttb", (unsigned long)ttb, SZ_16K))
> -			/*
> -			 * This can mean that:
> -			 * - the early MMU code has put the ttb into a place
> -			 *   which we don't have inside our available memory
> -			 * - Somebody else has occupied the ttb region which means
> -			 *   the ttb will get corrupted.
> -			 */
> -			pr_crit("Critical Error: Can't request SDRAM region for ttb at %p\n",
> +		pr_crit("Critical Error: Can't request SDRAM region for ttb at %p\n",
>  					ttb);
> -	} else {
> -		ttb = xmemalign(ARM_TTB_SIZE, ARM_TTB_SIZE);
> -
> -		set_ttbr(ttb);
> -
> -		/* For the XN bit to take effect, we can't be using DOMAIN_MANAGER. */
> -		if (cpu_architecture() >= CPU_ARCH_ARMv7)
> -			set_domain(DOMAIN_CLIENT);
> -		else
> -			set_domain(DOMAIN_MANAGER);
> -
> -		create_flat_mapping(ttb);
> -		__mmu_cache_flush();
> -	}
>  
>  	pr_debug("ttb: 0x%p\n", ttb);
>  
> @@ -499,8 +474,6 @@ void __mmu_init(bool mmu_on)
>  				PMD_SECT_DEF_CACHED);
>  		__mmu_cache_flush();
>  	}
> -
> -	__mmu_cache_on();

I guess it's ok to drop this, but some assurance in the commit message
would be nice.

>  }
>  
>  /*

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