[PATCH 2/2] ARM: imx6q: add cpu suspend/resume support in IRAM

[Linus Walleij]

On Sat, Dec 31, 2011 at 7:23 AM, Jason Chen <jason.chen at linaro.org> wrote:

>  void __init imx6q_pm_init(void)
>  {
>        /*
> @@ -67,4 +153,38 @@ void __init imx6q_pm_init(void)
>        phys_l2x0_saved_regs = __pa(&l2x0_saved_regs);
>
>        suspend_set_ops(&imx6q_pm_ops);
> +
> +       /* Move suspend routine into iRAM */
(...)
> diff --git a/arch/arm/mach-imx/suspend-imx6q.S b/arch/arm/mach-imx/suspend-imx6q.S
(...)
> +.macro ddr_io_save
> +       ldr     r4, [r9, #0x5ac] /* DRAM_DQM0 */
> +       ldr     r5, [r9, #0x5b4] /* DRAM_DQM1 */
> +       ldr     r6, [r9, #0x528] /* DRAM_DQM2 */
> +       ldr     r7, [r9, #0x520] /* DRAM_DQM3 */
> +       stmfd   sp!, {r4-r7}
(etc)

This is not an elegant solution. I know other platforms have
done similar things but it's still not elegant.

What we need it real handling of the on-chip memory pool
and possibility to compile and link directly into the
on-chip memory areas.

Compare to what we have for TCM:
Documentation/arm/tcm.txt
Implemented in:
arch/arm/kernel/tcm.c
Linker trickery in:
arch/arm/kernel/vmlinux.lds.S

An approach similar to this would make it possible to:

- Manage the on-chip heap in a structured way

- Write the above assembler code in C and compile it directly
  into on-chip RAM

- Share the same code with other archs and possibly merge
  it with some of the TCM handling code top create common
  onchip RAM handling

- Optionally free up the .TEXT memory pages used by this
  code after copying it to on-chip RAM (if that RAM is
  persistent, as it seems to be)

- Make it possible to define MT_MEMORY_ONCHIP (if
  MT_MEMORY_ITCM isn't good enough) in
  arch/arm/include/asm/mach/map.h so everybody can
  use this.

It is also a bit more work and patch iteration involved.
But the end solution is very appealing IMO. Also,
multi-platform binaries will complicate the above a bit
(especially if, say, two platforms have their on-chip
RAM in the same location...) but I am sure it can be
solved with proper cleverness and step-by-step measures.

Yours,
Linus Walleij