[PATCH v3 4/9] arm: armv7: save boot arguments

[Simon Glass]

Hi Raymond,

On Wed, Dec 27, 2023 at 3:52 PM Raymond Mao <raymond.mao at linaro.org> wrote:
>
> Hi Simon,
>
> On Tue, 26 Dec 2023 at 04:48, Simon Glass <sjg at chromium.org> wrote:
>>
>> Hi Raymond,
>>
>> On Fri, Dec 22, 2023 at 9:31 PM Raymond Mao <raymond.mao at linaro.org> wrote:
>> >
>> > Save boot arguments r[0-3] into an array for handover of bloblist from
>> > previous boot stage.
>> >
>> > Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
>> > ---
>> > Changes in v2
>> > - New patch file created for v2.
>> > Changes in v3
>> > - Swap value of r0 with r2.
>> >
>> >  arch/arm/cpu/armv7/start.S | 13 +++++++++++++
>> >  1 file changed, 13 insertions(+)
>> >
>> > diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
>> > index 69e281b086..2ca63ca32c 100644
>> > --- a/arch/arm/cpu/armv7/start.S
>> > +++ b/arch/arm/cpu/armv7/start.S
>> > @@ -152,9 +152,22 @@ ENDPROC(c_runtime_cpu_setup)
>> >   *
>> >   *************************************************************************/
>> >  WEAK(save_boot_params)
>> > +#if (IS_ENABLED(CONFIG_OF_BOARD) && IS_ENABLED(CONFIG_BLOBLIST))
>> > +       ldr r12, =saved_args
>> > +       /* Intentionally swapping r0 with r2 */
>> > +       stm r12, {r2, r1, r0, r3}
>>
>> I thought the instruction was a bitmap, so what does the 'swapping'
>> actually change?
>>
> The swapping is due to different register conventions between aarch32 and aarch64.
> Actually swapping here is to avoid the complexity of swapping this in C code.
> I will update the comments here.
>
> [...]

But how does this work? stm does not support changing the
ordering...what am I missing?

Regards,
Simon