[U-Boot] [PATCH 1/1] arm: armv7: enable unaligned access

[Heinrich Schuchardt]

On 03/30/2018 01:36 AM, Siarhei Siamashka wrote:
> On Thu, 29 Mar 2018 23:33:50 +0200
> Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> 
>> We use the command bootefi to run UEFI executables like GRUB and iPXE.
>> The UEFI spec requires that unaligned access is enabled if the CPU
>> supports it. This is true for armv7.
>>
>> So we should not set bit 1 of the system control register, the alignment
>> bit.
>>
>> Without this patch iPXE snp.efi cannot be executed on the Allwinner A20.
>>
>> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
>> ---
>>  arch/arm/cpu/armv7/start.S | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
>> index 7e2695761e..1771741119 100644
>> --- a/arch/arm/cpu/armv7/start.S
>> +++ b/arch/arm/cpu/armv7/start.S
>> @@ -150,7 +150,6 @@ ENTRY(cpu_init_cp15)
>>  	mrc	p15, 0, r0, c1, c0, 0
>>  	bic	r0, r0, #0x00002000	@ clear bits 13 (--V-)
>>  	bic	r0, r0, #0x00000007	@ clear bits 2:0 (-CAM)
>> -	orr	r0, r0, #0x00000002	@ set bit 1 (--A-) Align
>>  	orr	r0, r0, #0x00000800	@ set bit 11 (Z---) BTB
>>  #ifdef CONFIG_SYS_ICACHE_OFF
>>  	bic	r0, r0, #0x00001000	@ clear bit 12 (I) I-cache
> 
> Can you postpone flipping this bit until the very moment when you
> are about to start your UEFI executable?
> 
> The main reason against setting this bit for the whole U-Boot
> globally is that a lot of common code in U-Boot can be run on
> different CPU architectures, including those which don't
> support unaligned memory accesses (ARMv5, MIPS, ...). This
> is a maintenance nightmare. Because the people, who test their
> patches only on ARMv7 hardware, will unintentionally keep
> breaking other architectures.
> 

Hello Siarhei,

we could clear the bit when the bootefi command is invoked.

Best regards

Heinrich