[PATCH v5 7/8] firmware: Improve fw_boot_hart

[Anup Patel]

On Sat, Mar 2, 2024 at 1:13 PM Xiang W <wxjstz at 126.com> wrote:
>
> Improve fw_boot_hart to reduce parameter saving and restoration.
>
> Signed-off-by: Xiang W <wxjstz at 126.com>
> ---
>  firmware/fw_base.S    |  7 ++-----
>  firmware/fw_dynamic.S | 24 ++++++++++++------------
>  firmware/fw_jump.S    |  6 +++---
>  firmware/fw_payload.S |  6 +++---
>  4 files changed, 20 insertions(+), 23 deletions(-)
>
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index a798545..df5f769 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -38,14 +38,11 @@
>         .globl _start_warm
>  _start:
>         /* Find preferred boot HART id */
> -       MOV_3R  s0, a0, s1, a1, s2, a2
>         call    fw_boot_hart
> -       add     a6, a0, zero
> -       MOV_3R  a0, s0, a1, s1, a2, s2

NACK to this patch.

In future, someone might accidentally clobber the
a0 to a2 registers in fw_boot_hart without knowing
that caller is not preserving.

This patch achieves 0 improvement.

>         li      a7, -1
> -       beq     a6, a7, _try_lottery
> +       beq     t0, a7, _try_lottery
>         /* Jump to relocation wait loop if we are not boot hart */
> -       bne     a0, a6, _wait_for_boot_hart
> +       bne     a0, t0, _wait_for_boot_hart
>  _try_lottery:
>         /* Jump to relocation wait loop if we don't get relocation lottery */
>         lla     a6, _boot_status
> diff --git a/firmware/fw_dynamic.S b/firmware/fw_dynamic.S
> index 5ee2883..52ef320 100644
> --- a/firmware/fw_dynamic.S
> +++ b/firmware/fw_dynamic.S
> @@ -17,24 +17,24 @@
>         /*
>          * This function is called very early even before
>          * fw_save_info() is called.
> -        * We can only use a0, a1, and a2 registers here.
> -        * The boot HART id should be returned in 'a0'.
> +        * We can only use t0, t1, and t2 registers here.
> +        * The boot HART id should be returned in 't0'.
>          */
>  fw_boot_hart:
>         /* Sanity checks */
> -       li      a1, FW_DYNAMIC_INFO_MAGIC_VALUE
> -       REG_L   a0, FW_DYNAMIC_INFO_MAGIC_OFFSET(a2)
> -       bne     a0, a1, _start_hang
> -       li      a1, FW_DYNAMIC_INFO_VERSION_MAX
> -       REG_L   a0, FW_DYNAMIC_INFO_VERSION_OFFSET(a2)
> -       bgt     a0, a1, _start_hang
> +       li      t1, FW_DYNAMIC_INFO_MAGIC_VALUE
> +       REG_L   t0, FW_DYNAMIC_INFO_MAGIC_OFFSET(a2)
> +       bne     t0, t1, _start_hang
> +       li      t1, FW_DYNAMIC_INFO_VERSION_MAX
> +       REG_L   t0, FW_DYNAMIC_INFO_VERSION_OFFSET(a2)
> +       bgt     t0, t1, _start_hang
>
>         /* Read boot HART id */
> -       li      a1, FW_DYNAMIC_INFO_VERSION_2
> -       blt     a0, a1, 2f
> -       REG_L   a0, FW_DYNAMIC_INFO_BOOT_HART_OFFSET(a2)
> +       li      t1, FW_DYNAMIC_INFO_VERSION_2
> +       blt     t0, t1, 2f
> +       REG_L   t0, FW_DYNAMIC_INFO_BOOT_HART_OFFSET(a2)
>         ret
> -2:     li      a0, -1
> +2:     li      t0, -1
>         ret
>
>         .section .entry, "ax", %progbits
> diff --git a/firmware/fw_jump.S b/firmware/fw_jump.S
> index ebf297f..ba46697 100644
> --- a/firmware/fw_jump.S
> +++ b/firmware/fw_jump.S
> @@ -15,11 +15,11 @@
>         /*
>          * This function is called very early even before
>          * fw_save_info() is called.
> -        * We can only use a0, a1, and a2 registers here.
> -        * The boot HART id should be returned in 'a0'.
> +        * We can only use t0, t1, and t2 registers here.
> +        * The boot HART id should be returned in 't0'.
>          */
>  fw_boot_hart:
> -       li      a0, -1
> +       li      t0, -1
>         ret
>
>         .section .entry, "ax", %progbits
> diff --git a/firmware/fw_payload.S b/firmware/fw_payload.S
> index 3c8433e..02fd172 100644
> --- a/firmware/fw_payload.S
> +++ b/firmware/fw_payload.S
> @@ -15,11 +15,11 @@
>         /*
>          * This function is called very early even before
>          * fw_save_info() is called.
> -        * We can only use a0, a1, and a2 registers here.
> -        * The boot HART id should be returned in 'a0'.
> +        * We can only use t0, t1, and t2 registers here.
> +        * The boot HART id should be returned in 't0'.
>          */
>  fw_boot_hart:
> -       li      a0, -1
> +       li      t0, -1
>         ret
>
>         .section .entry, "ax", %progbits
> --
> 2.43.0
>

Regards,
Anup