[PATCH] arm: mxs: Clear CPSR V bit to activate low vectors

[Stefano Babic]

Hi Marek, Lukasz,

On 31.07.23 10:06, Lukasz Majewski wrote:
> On Sat, 29 Jul 2023 15:30:10 +0200
> Marek Vasut <marex at denx.de> wrote:
> 
>> The MXS starts with CPSR V bit set, which makes the CPU jump to high
>> vectors in case of an exception. Those high vectors are located at
>> 0xffff0000, which is where the BootROM exception table is located as
>> well. U-Boot should handle exceptions on its own using its own
>> exception handling code, which is located at 0x0, i.e. at low
>> vectors. Clear the CPSR V bit, so that the CPU would jump to low
>> vectors on exception instead, and therefore run the U-Boot exception
>> handling code.
>>
>> Signed-off-by: Marek Vasut <marex at denx.de>
>> ---
>> Cc: "NXP i.MX U-Boot Team" <uboot-imx at nxp.com>
>> Cc: Fabio Estevam <festevam at gmail.com>
>> Cc: Lukasz Majewski <lukma at denx.de>
>> Cc: Stefano Babic <sbabic at denx.de>
>> ---
>>   arch/arm/cpu/arm926ejs/mxs/mxs.c      | 3 +++
>>   arch/arm/cpu/arm926ejs/mxs/spl_boot.c | 4 ++++
>>   2 files changed, 7 insertions(+)
>>
>> diff --git a/arch/arm/cpu/arm926ejs/mxs/mxs.c
>> b/arch/arm/cpu/arm926ejs/mxs/mxs.c index 4d21e3df76e..d64a8328b04
>> 100644 --- a/arch/arm/cpu/arm926ejs/mxs/mxs.c
>> +++ b/arch/arm/cpu/arm926ejs/mxs/mxs.c
>> @@ -85,6 +85,9 @@ void mx28_fixup_vt(uint32_t start_addr)
>>   		/* cppcheck-suppress nullPointer */
>>   		vt[i + 8] = start_addr + (4 * i);
>>   	}
>> +
>> +	/* Make sure ARM core points to low vectors */
>> +	set_cr(get_cr() & ~CR_V);
>>   }
>>   
>>   #ifdef	CONFIG_ARCH_MISC_INIT
>> diff --git a/arch/arm/cpu/arm926ejs/mxs/spl_boot.c
>> b/arch/arm/cpu/arm926ejs/mxs/spl_boot.c index
>> 5598c552ab9..4a7dfc6a2ae 100644 ---
>> a/arch/arm/cpu/arm926ejs/mxs/spl_boot.c +++
>> b/arch/arm/cpu/arm926ejs/mxs/spl_boot.c @@ -17,6 +17,7 @@
>>   #include <asm/arch/sys_proto.h>
>>   #include <asm/gpio.h>
>>   #include <asm/sections.h>
>> +#include <asm/system.h>
>>   #include <linux/compiler.h>
>>   
>>   #include "mxs_init.h"
>> @@ -104,6 +105,9 @@ static void mxs_spl_fixup_vectors(void)
>>   
>>   	/* cppcheck-suppress nullPointer */
>>   	memcpy(0x0, &_start, 0x60);
>> +
>> +	/* Make sure ARM core points to low vectors */
>> +	set_cr(get_cr() & ~CR_V);
>>   }
>>   
>>   static void mxs_spl_console_init(void)
> 
> Reviewed-by: Lukasz Majewski <lukma at denx.de>
> 

Thanks for raising my attention to this older patch, but it breaks 
exaclty the xea board:

+{standard input}: Assembler messages:
+{standard input}:214: Error: selected processor does not support `mrc 
p15,0,r3,c1,c0,0' in Thumb mode
+{standard input}:249: Error: selected processor does not support `mcr 
p15,0,r3,c1,c0,0' in Thumb mode
+{standard input}:157: Error: selected processor does not support `mrc 
p15,0,r3,c1,c0,0' in Thumb mode
+{standard input}:188: Error: selected processor does not support `mcr 
p15,0,r3,c1,c0,0' in Thumb mode

Can you check it ?

Regards,
Stefano

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