[U-Boot] [PATCH 05/12] arm: Don't try to support CONFIG_ARMV7_LPAE on ARMv4T

[Simon Glass]

Hi Tom.

On 22 May 2017 at 19:15, Tom Rini <trini at konsulko.com> wrote:
> On Mon, May 22, 2017 at 05:17:25AM -0600, Simon Glass wrote:
>
>> At present if CONFIG_ARMV7_LPAE is defined then mmu_setup() will use
>> instructions which are invalid on ARMv4T. This happens on Tegra since it
>> has an ARMv4T boot CPU. Add a check for the architecture version to allow
>> the code to be built. It will not actually be executed by the boot CPU,
>> but needs to compile.
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>> ---
>>
>>  arch/arm/lib/cache-cp15.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/lib/cache-cp15.c b/arch/arm/lib/cache-cp15.c
>> index 0f7020a315..f293573601 100644
>> --- a/arch/arm/lib/cache-cp15.c
>> +++ b/arch/arm/lib/cache-cp15.c
>> @@ -129,7 +129,7 @@ static inline void mmu_setup(void)
>>               dram_bank_mmu_setup(i);
>>       }
>>
>> -#ifdef CONFIG_ARMV7_LPAE
>> +#if defined(CONFIG_ARMV7_LPAE) && __LINUX_ARM_ARCH__ != 4
>>       /* Set up 4 PTE entries pointing to our 4 1GB page tables */
>>       for (i = 0; i < 4; i++) {
>>               u64 *page_table = (u64 *)(gd->arch.tlb_addr + (4096 * 4));
>
> Wait, how do we get to this situation again, and how does it end up
> being OK?  SPL gets built for ARMv4T and U-Boot proper is built for v7,
> and we end up doing LPAE enable in full U-Boot?

Eek sorry I missed this question. The problem is that with ARMv4T this
code does not currently build. On Tegra, if we enable
CONFIG_ARMV7_LPAE, this code runs on ARMv7, but it still compiled by
the ARMv7 boot CPU. So the change here is to make sure it is not
compiled for ARMv4T.

Another way of thinking about this is that ARMv4T does not support
LPAE but we have no way to enable the option only for ARMv7. Both CPUs
compile the same code. The __LINUX_ARM_ARCH__ option helps with this.

Regards,
Simon