Re: [Qemu-devel] [PATCH 5/7] hw/arm/boot: Allow easier swapping in of different loader code

[Peter Crosthwaite]

On Fri, Dec 13, 2013 at 8:05 PM, Peter Maydell <address@hidden> wrote:
> On 13 December 2013 03:19, Peter Crosthwaite
> <address@hidden> wrote:
>> Why do we need blobs at all? Cant we just fix arm/boot to directly
>> setup the CPU state to the desired? Rather than complex blobs that
>> execute ARM instructions just manipulate the regs directly.
>
> We could in theory do this for the primary bootloader, but
> the secondary CPU blob has to have a loop in it so we
> can sit around waiting for the guest code running in the
> primary to tell us it's time to go:
>
>>> +static const ARMInsnFixup smpboot[] = {
>>> +    { 0xe59f2028 }, /* ldr r2, gic_cpu_if */
>>> +    { 0xe59f0028 }, /* ldr r0, startaddr */
>>> +    { 0xe3a01001 }, /* mov r1, #1 */
>>> +    { 0xe5821000 }, /* str r1, [r2] - set GICC_CTLR.Enable */
>>> +    { 0xe3a010ff }, /* mov r1, #0xff */
>>> +    { 0xe5821004 }, /* str r1, [r2, 4] - set GIC_PMR.Priority to 0xff */
>>> +    { 0, FIXUP_DSB },   /* dsb */
>>> +    { 0xe320f003 }, /* wfi */
>>> +    { 0xe5901000 }, /* ldr     r1, [r0] */
>>> +    { 0xe1110001 }, /* tst     r1, r1 */
>>> +    { 0x0afffffb }, /* beq     <wfi> */
>>> +    { 0xe12fff11 }, /* bx      r1 */
>>> +    { 0, FIXUP_GIC_CPU_IF },


Reading up on Christopher's Kernel documentation link:

Documentation/arm64/booting.txt
Documentation/arm/Booting

I can't see any reference to GIC, where are these GICisms coming from?

>>> +    { 0, FIXUP_BOOTREG },
>>> +    { 0, FIXUP_TERMINATOR }
>>>  };
>
> We're also writing to devices here, and it's cleaner to do that
> by running a guest code instruction than by somehow having
> the boot code ferret around inside the device's implementation
> pre-start, I think.

dma_memory_write(&address_space_memory, ...

Its a level above ferreting, and a level below the machine code blob.

Regards,
Peter

>
> thanks
> -- PMM
>