Re: [PATCH v3] riscv: add BUILTIN_DTB support for MMU-enabled targets

[Palmer Dabbelt]

On Fri, 15 Jan 2021 15:49:48 PST (-0800), vitaly.wool@xxxxxxxxxxxx wrote:
> Sometimes, especially in a production system we may not want to
> use a "smart bootloader" like u-boot to load kernel, ramdisk and
> device tree from a filesystem on eMMC, but rather load the kernel
> from a NAND partition and just run it as soon as we can, and in
> this case it is convenient to have device tree compiled into the
> kernel binary. Since this case is not limited to MMU-less systems,
> let's support it for these which have MMU enabled too.
>
> While at it, provide __dtb_start as a parameter to setup_vm() in
> BUILTIN_DTB case, so we don't have to duplicate BUILTIN_DTB specific
> processing in MMU-enabled and MMU-disabled versions of setup_vm().
>
> Signed-off-by: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
> ---
> Changes from v2:
> * folded "RISC-V: simplify BUILTIN_DTB processing" patch
> [http://lists.infradead.org/pipermail/linux-riscv/2021-January/004153.html]
> Changes from v1:
> * no direct initial_boot_params assignment
> * skips the temporary mapping for DT if BUILTIN_DTB=y
>
>  arch/riscv/Kconfig       |  1 -
>  arch/riscv/kernel/head.S |  4 ++++
>  arch/riscv/mm/init.c     | 19 +++++++++++++------
>  3 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2ef05ef921b5..444a1ed1e847 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -445,7 +445,6 @@ endmenu
>
>  config BUILTIN_DTB
>  	def_bool n
> -	depends on RISCV_M_MODE
>  	depends on OF
>
>  menu "Power management options"
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 16e9941900c4..f5a9bad86e58 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -260,7 +260,11 @@ clear_bss_done:
>
>  	/* Initialize page tables and relocate to virtual addresses */
>  	la sp, init_thread_union + THREAD_SIZE
> +#ifdef CONFIG_BUILTIN_DTB
> +	la a0, __dtb_start
> +#else
>  	mv a0, s1
> +#endif /* CONFIG_BUILTIN_DTB */
>  	call setup_vm
>  #ifdef CONFIG_MMU
>  	la a0, early_pg_dir
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 30b61f2c6b87..45faad7c4291 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -192,10 +192,13 @@ void __init setup_bootmem(void)
>  #endif /* CONFIG_BLK_DEV_INITRD */
>
>  	/*
> -	 * Avoid using early_init_fdt_reserve_self() since __pa() does
> +	 * If DTB is built in, no need to reserve its memblock.
> +	 * Otherwise, do reserve it but avoid using
> +	 * early_init_fdt_reserve_self() since __pa() does
>  	 * not work for DTB pointers that are fixmap addresses
>  	 */
> -	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));
>
>  	early_init_fdt_scan_reserved_mem();
>  	dma_contiguous_reserve(dma32_phys_limit);
> @@ -499,6 +502,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	/* Setup early PMD for DTB */
>  	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
>  			   (uintptr_t)early_dtb_pmd, PGDIR_SIZE, PAGE_TABLE);
> +#ifndef CONFIG_BUILTIN_DTB
>  	/* Create two consecutive PMD mappings for FDT early scan */
>  	pa = dtb_pa & ~(PMD_SIZE - 1);
>  	create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA,
> @@ -506,7 +510,11 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	create_pmd_mapping(early_dtb_pmd, DTB_EARLY_BASE_VA + PMD_SIZE,
>  			   pa + PMD_SIZE, PMD_SIZE, PAGE_KERNEL);
>  	dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PMD_SIZE - 1));
> +#else /* CONFIG_BUILTIN_DTB */
> +	dtb_early_va = __va(dtb_pa);
> +#endif /* CONFIG_BUILTIN_DTB */
>  #else
> +#ifndef CONFIG_BUILTIN_DTB
>  	/* Create two consecutive PGD mappings for FDT early scan */
>  	pa = dtb_pa & ~(PGDIR_SIZE - 1);
>  	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA,
> @@ -514,6 +522,9 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	create_pgd_mapping(early_pg_dir, DTB_EARLY_BASE_VA + PGDIR_SIZE,
>  			   pa + PGDIR_SIZE, PGDIR_SIZE, PAGE_KERNEL);
>  	dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PGDIR_SIZE - 1));
> +#else /* CONFIG_BUILTIN_DTB */
> +	dtb_early_va = __va(dtb_pa);
> +#endif /* CONFIG_BUILTIN_DTB */
>  #endif
>  	dtb_early_pa = dtb_pa;
>
> @@ -604,11 +615,7 @@ static void __init setup_vm_final(void)
>  #else
>  asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  {
> -#ifdef CONFIG_BUILTIN_DTB
> -	dtb_early_va = (void *) __dtb_start;
> -#else
>  	dtb_early_va = (void *)dtb_pa;
> -#endif
>  	dtb_early_pa = dtb_pa;
>  }

Thanks, this is on for-next.