linux-kernel - Re: [PATCH -fixes 2/2] riscv: Do not set initial_boot

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Date:   Mon, 27 Mar 2023 12:16:40 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
CC:     Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, <linux-doc@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -fixes 2/2] riscv: Do not set initial_boot_params to the
 linear address of the dtb

On Thu, Mar 23, 2023 at 05:33:47PM +0100, Alexandre Ghiti wrote:
> Now that the dtb early mapping was moved in the fixmap region, we can
> keep using this address since it is present in swapper_pg_dir, so remove
> the dtb relocation which was wrong anyway since early_memremap is
> restricted to 256K whereas the maximum fdt size is 2MB.

I feel bad making this comment since only one of us is a native speaker,
but for the future would you mind breaking up overly long sentences like
the above? Say:

	Now that the dtb early mapping was moved in the fixmap region, we can
	keep using this address since it is present in swapper_pg_dir, and
	remove the dtb relocation.
	The relocation was wrong anyway since early_memremap() is restricted to
	256K whereas the maximum fdt size is 2MB.

> 
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
>  arch/riscv/kernel/setup.c |  5 +----
>  arch/riscv/mm/init.c      | 21 ++-------------------
>  2 files changed, 3 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 542eed85ad2c..a059b73f4ddb 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -278,10 +278,7 @@ void __init setup_arch(char **cmdline_p)
>  #if IS_ENABLED(CONFIG_BUILTIN_DTB)
>  	unflatten_and_copy_device_tree();
>  #else
> -	if (early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa))))

btw, how come it is safe now to drop this? This feels like a separate
change that should be its own commit, no?

Cheers,
Conor.

> -		unflatten_device_tree();
> -	else
> -		pr_err("No DTB found in kernel mappings\n");
> +	unflatten_device_tree();
>  #endif
>  	misc_mem_init();
>  
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index fb78d6bbabae..0f14f4a8d179 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -249,25 +249,8 @@ static void __init setup_bootmem(void)
>  	 * early_init_fdt_reserve_self() since __pa() does
>  	 * not work for DTB pointers that are fixmap addresses
>  	 */
> -	if (!IS_ENABLED(CONFIG_BUILTIN_DTB)) {
> -		/*
> -		 * In case the DTB is not located in a memory region we won't
> -		 * be able to locate it later on via the linear mapping and
> -		 * get a segfault when accessing it via __va(dtb_early_pa).
> -		 * To avoid this situation copy DTB to a memory region.
> -		 * Note that memblock_phys_alloc will also reserve DTB region.
> -		 */
> -		if (!memblock_is_memory(dtb_early_pa)) {
> -			size_t fdt_size = fdt_totalsize(dtb_early_va);
> -			phys_addr_t new_dtb_early_pa = memblock_phys_alloc(fdt_size, PAGE_SIZE);
> -			void *new_dtb_early_va = early_memremap(new_dtb_early_pa, fdt_size);
> -
> -			memcpy(new_dtb_early_va, dtb_early_va, fdt_size);
> -			early_memunmap(new_dtb_early_va, fdt_size);
> -			_dtb_early_pa = new_dtb_early_pa;
> -		} else
> -			memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> -	}
> +	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
> +		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
>  
>  	dma_contiguous_reserve(dma32_phys_limit);
>  	if (IS_ENABLED(CONFIG_64BIT))
> -- 
> 2.37.2
> 
> 

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