[U-Boot] [PATCH V2] mx28: fix SPL code to make USB booting work

[Matthias Fuchs]

On 06.02.2012 16:29, Marek Vasut wrote:
>> This patch fixes booting i.MX28 CPUs via USB download.
>> In this mode the CPU's bootrom implements a USB HID device that
>> accepts a bootstream.
>>
>> When downloading the bootstream via USB, first the SPL code is
>> received and executed. Then the u-boot image is received and
>> called.
>>
>> The USB bootmode is interrupt driven.
>>
>> This patch fixes two things:
>>
>> 1) The ARM's fast interrupt mode is disabled when the SPL code
>> has been run. So save and restore the CPSR register.
>>
>> 2) The exception vector location is set back to bootrom space to
>> make the USB interrupts work again. The SPL code needs to change this
>> option for the ram size probing.
>>
>> Signed-off-by: Matthias Fuchs <matthias.fuchs at esd.eu>
>> ---
>> changes in v2:
>>  - store old SPSR on stack instead of jiggling around with some bits
>>  - remove #ifndef CONFIG_SKIP_LOWLEVEL_INIT
>>
>>  arch/arm/cpu/arm926ejs/mx28/start.S |   15 +++++++++++++++
>>  1 files changed, 15 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/cpu/arm926ejs/mx28/start.S
>> b/arch/arm/cpu/arm926ejs/mx28/start.S index 2cd4d73..69d911b 100644
>> --- a/arch/arm/cpu/arm926ejs/mx28/start.S
>> +++ b/arch/arm/cpu/arm926ejs/mx28/start.S
>> @@ -171,6 +171,7 @@ _reset:
>>  	 * set the cpu to SVC32 mode
>>  	 */
>>  	mrs	r0,cpsr
>> +	push	{r0}
>>  	bic	r0,r0,#0x1f
>>  	orr	r0,r0,#0xd3
>>  	msr	cpsr,r0
>> @@ -185,6 +186,20 @@ _reset:
>>
>>  	bl	board_init_ll
>>
>> +	/*
>> +	 * restore bootrom's cpu mode (especially FIQ)
>> +	 */
>> +	pop	{r0}
>> +	msr	cpsr,r0
>> +
>> +	/*
>> +	 * set exception vector location back to bootrom space.
>> +	 * (required by bootrom for USB boot)
>> +	 */
>> +	mrc	p15, 0, r0, c1, c0, 0
>> +	orr	r0, r0, #0x00002000	/* set bit 13 'V' */
>> +	mcr	p15, 0, r0, c1, c0, 0
> 
> Maybe you can save this register too, like you did with CPSR?
Can do.

Done. Works. Patch V3 follows.
> 
> Otherwise, it looks good.
> 
> btw plain "push r0" doesn't work?
No.

Matthias