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References: <20221128152442.3403-1-jszhang@kernel.org>
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From:   Atish Kumar Patra <atishp@rivosinc.com>
Date:   Mon, 28 Nov 2022 12:11:49 -0800
Message-ID: <CAHBxVyHg0fU9msnV4vgp4oK6aZZv+nc9mFTbTRjHNsgJAG0eyg@mail.gmail.com>
Subject: Re: [PATCH] riscv: head: use 0 as the default text_offset
To:     Jisheng Zhang <jszhang@kernel.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
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On Mon, Nov 28, 2022 at 7:34 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> Commit 0f327f2aaad6 ("RISC-V: Add an Image header that boot loader can
> parse.") adds an image header which "is based on ARM64 boot image
> header and provides an opportunity to combine both ARM64 & RISC-V
> image headers in future.". At that time, arm64's default text_offset
> is 0x80000, this is to give "512 KB of guaranteed BSS space to put
> the swapper page tables" as commit cfa7ede20f13 ("arm64: set TEXT_OFFSET
> to 0x0 in preparation for removing it entirely") pointed out, but
> riscv doesn't need the space, so use 0 as the default text_offset.
>
> Before this patch, booting linux kernel on Sipeed bl808 M1s Dock
> with u-boot booti cmd:
> [    0.000000] OF: fdt: Ignoring memory range 0x50000000 - 0x50200000
> ...
> [    0.000000]   DMA32    [mem 0x0000000050200000-0x0000000053ffffff]
> As can be seen, 2MB DDR(0x50000000 - 0x501fffff) can't be used by
> linux.
>
> After this patch, the 64MB DDR is fully usable by linux
> [    0.000000]   DMA32    [mem 0x0000000050000000-0x0000000053ffffff]
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  arch/riscv/kernel/head.S | 12 +-----------
>  1 file changed, 1 insertion(+), 11 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index b865046e4dbb..ef95943f7a70 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -38,18 +38,8 @@ ENTRY(_start)
>         .word 0
>  #endif
>         .balign 8
> -#ifdef CONFIG_RISCV_M_MODE
> -       /* Image load offset (0MB) from start of RAM for M-mode */
> +       /* Image load offset (0MB) from start of RAM */
>         .dword 0
> -#else
> -#if __riscv_xlen == 64
> -       /* Image load offset(2MB) from start of RAM */
> -       .dword 0x200000
> -#else
> -       /* Image load offset(4MB) from start of RAM */
> -       .dword 0x400000
> -#endif
> -#endif

NACK.
RV64 needs to boot at a 2MB aligned address and RV32 needs to boot at
a 4MB aligned address.
The firmware is assumed to live at the start of DRAM for Linux running
in S-mode.


>         /* Effective size of kernel image */
>         .dword _end - _start
>         .dword __HEAD_FLAGS
> --
> 2.37.2
>