[U-Boot] [PATCH V3] mx28: fix SPL code to make USB booting work

Stefano Babic
2012-02-07T16:56:30Z

On 07/02/2012 17:54, 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) Save and restore c1 control register: the exception vector
>> location needs to be 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@esd.eu>
>> ---
>> changes in v2:
>> - store old SPSR on stack instead of jiggling around with some bits
>> - remove #ifndef CONFIG_SKIP_LOWLEVEL_INIT
>> changes in v3:
>> - also store C1 register on stack
>>
>> arch/arm/cpu/arm926ejs/mx28/start.S | 21 ++++++++++++++++++++-
>> 1 files changed, 20 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/cpu/arm926ejs/mx28/start.S
>> b/arch/arm/cpu/arm926ejs/mx28/start.S index 2cd4d73..e572b78 100644
>> --- a/arch/arm/cpu/arm926ejs/mx28/start.S
>> +++ b/arch/arm/cpu/arm926ejs/mx28/start.S
>> @@ -167,10 +167,15 @@ _reset:
>> */
>> push {r0-r12,r14}
>>
>> + /* save control register c1 */
>> + mrc p15, 0, r0, c1, c0, 0
>> + push {r0}
>> +
>> /*
>> - * set the cpu to SVC32 mode
>> + * set the cpu to SVC32 mode and store old CPSR register content
>> */
>> mrs r0,cpsr
>> + push {r0}
>> bic r0,r0,#0x1f
>> orr r0,r0,#0xd3
>> msr cpsr,r0
>> @@ -185,6 +190,20 @@ _reset:
>>
>> bl board_init_ll
>>
>> + /*
>> + * restore bootrom's cpu mode (especially FIQ)
>> + */
>> + pop {r0}
>> + msr cpsr,r0
>> +
>> + /*
>> + * restore c1 register
>> + * (especially set exception vector location back to
>> + * bootrom space which is required by bootrom for USB boot)
>> + */
>> + pop {r0}
>> + mcr p15, 0, r0, c1, c0, 0
>> +
>> pop {r0-r12,r14}
>> bx lr
>
> Yep, looks fine. Stefano, can you apply? Or shall I start hand-picking these
> mx28 patches and then send you a pullrq?

No problem, I will apply it to u-boot-imx

Stefano

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