Re: [PATCH v2] riscv: errata: andes: Probe for IOCP only once in boot stage

[Geert Uytterhoeven]

Hi Prabhakar,

On Thu, Nov 30, 2023 at 1:56 PM Prabhakar <prabhakar.csengg@xxxxxxxxx> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
>
> We need to probe for IOCP only once during boot stage, as we were probing
> for IOCP for all the stages this caused the below issue during module-init
> stage,
>
> [9.019104] Unable to handle kernel paging request at virtual address ffffffff8100d3a0
> [9.027153] Oops [#1]
> [9.029421] Modules linked in: rcar_canfd renesas_usbhs i2c_riic can_dev spi_rspi i2c_core
> [9.037686] CPU: 0 PID: 90 Comm: udevd Not tainted 6.7.0-rc1+ #57
> [9.043756] Hardware name: Renesas SMARC EVK based on r9a07g043f01 (DT)
> [9.050339] epc : riscv_noncoherent_supported+0x10/0x3e
> [9.055558]  ra : andes_errata_patch_func+0x4a/0x52
> [9.060418] epc : ffffffff8000d8c2 ra : ffffffff8000d95c sp : ffffffc8003abb00
> [9.067607]  gp : ffffffff814e25a0 tp : ffffffd80361e540 t0 : 0000000000000000
> [9.074795]  t1 : 000000000900031e t2 : 0000000000000001 s0 : ffffffc8003abb20
> [9.081984]  s1 : ffffffff015b57c7 a0 : 0000000000000000 a1 : 0000000000000001
> [9.089172]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : ffffffff8100d8be
> [9.096360]  a5 : 0000000000000001 a6 : 0000000000000001 a7 : 000000000900031e
> [9.103548]  s2 : ffffffff015b57d7 s3 : 0000000000000001 s4 : 000000000000031e
> [9.110736]  s5 : 8000000000008a45 s6 : 0000000000000500 s7 : 000000000000003f
> [9.117924]  s8 : ffffffc8003abd48 s9 : ffffffff015b1140 s10: ffffffff8151a1b0
> [9.125113]  s11: ffffffff015b1000 t3 : 0000000000000001 t4 : fefefefefefefeff
> [9.132301]  t5 : ffffffff015b57c7 t6 : ffffffd8b63a6000
> [9.137587] status: 0000000200000120 badaddr: ffffffff8100d3a0 cause: 000000000000000f
> [9.145468] [<ffffffff8000d8c2>] riscv_noncoherent_supported+0x10/0x3e
> [9.151972] [<ffffffff800027e8>] _apply_alternatives+0x84/0x86
> [9.157784] [<ffffffff800029be>] apply_module_alternatives+0x10/0x1a
> [9.164113] [<ffffffff80008fcc>] module_finalize+0x5e/0x7a
> [9.169583] [<ffffffff80085cd6>] load_module+0xfd8/0x179c
> [9.174965] [<ffffffff80086630>] init_module_from_file+0x76/0xaa
> [9.180948] [<ffffffff800867f6>] __riscv_sys_finit_module+0x176/0x2a8
> [9.187365] [<ffffffff80889862>] do_trap_ecall_u+0xbe/0x130
> [9.192922] [<ffffffff808920bc>] ret_from_exception+0x0/0x64
> [9.198573] Code: 0009 b7e9 6797 014d a783 85a7 c799 4785 0717 0100 (0123) aef7
> [9.205994] ---[ end trace 0000000000000000 ]---
>
> This is because we called riscv_noncoherent_supported() for all the stages
> during IOCP probe. riscv_noncoherent_supported() function sets
> noncoherent_supported variable to true which has an annotation set to
> "__ro_after_init" due to which we were seeing the above splat. Fix this by
> probing for IOCP only once in boot stage by having a boolean variable
> is_iocp_probe_done which will be set to true upon IOCP probe in
> errata_probe_iocp() and we bail out early if is_iocp_probe_done is set.
>
> While at it make return type of errata_probe_iocp() to void as we were
> not checking the return value in andes_errata_patch_func().
>
> Fixes: e021ae7f5145 ("riscv: errata: Add Andes alternative ports")
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> ---
> v1->v2
> * As RISCV_ALTERNATIVES_BOOT stage can happen twice add a is_iocp_probe_done
>   variable to probe for IOCP only once.
> * Updated commit message
> * Make return value of errata_probe_iocp() to void

Thanks for the update!

> --- a/arch/riscv/errata/andes/errata.c
> +++ b/arch/riscv/errata/andes/errata.c
> @@ -38,29 +38,36 @@ static long ax45mp_iocp_sw_workaround(void)
>         return ret.error ? 0 : ret.value;
>  }
>
> -static bool errata_probe_iocp(unsigned int stage, unsigned long arch_id, unsigned long impid)
> +static void errata_probe_iocp(unsigned int stage, unsigned long arch_id, unsigned long impid)
>  {
> +       static bool is_iocp_probe_done;

done?

> +
>         if (!IS_ENABLED(CONFIG_ERRATA_ANDES_CMO))
> -               return false;
> +               return;
> +
> +       if (is_iocp_probe_done)
> +               return;
>

Why not keep it simple, and just do

    done = true;

here?
Can arch_id or impid suddenly change, so you have to recheck?
If the SBI call in ax45mp_iocp_sw_workaround() fails, is there really
a need to try it again later?

>         if (arch_id != ANDESTECH_AX45MP_MARCHID || impid != ANDESTECH_AX45MP_MIMPID)
> -               return false;
> +               return;
>
> -       if (!ax45mp_iocp_sw_workaround())
> -               return false;
> +       if (!ax45mp_iocp_sw_workaround()) {
> +               is_iocp_probe_done = true;
> +               return;
> +       }
>
>         /* Set this just to make core cbo code happy */
>         riscv_cbom_block_size = 1;
>         riscv_noncoherent_supported();
> -
> -       return true;
> +       is_iocp_probe_done = true;
>  }

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds