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

[Anup Patel]

On Sat, Dec 26, 2020 at 10:03 PM Vitaly Wool <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.
>
> Signed-off-by: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
> ---
>  arch/riscv/Kconfig   |  1 -
>  arch/riscv/mm/init.c | 12 ++++++++++--
>  2 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2b41f6d8e458..9464b4e3a71a 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -419,7 +419,6 @@ endmenu
>
>  config BUILTIN_DTB
>         def_bool n
> -       depends on RISCV_M_MODE
>         depends on OF
>
>  menu "Power management options"
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 87c305c566ac..5d1c7a3ec01c 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -194,12 +194,20 @@ void __init setup_bootmem(void)
>         setup_initrd();
>  #endif /* CONFIG_BLK_DEV_INITRD */
>
> +       /*
> +        * If DTB is built in, no need to reserve its memblock.
> +        * OTOH, initial_boot_params has to be set to properly copy DTB
> +        * before unflattening later on.
> +        */
> +       if (IS_ENABLED(CONFIG_BUILTIN_DTB))
> +               initial_boot_params = __va(dtb_early_pa);

Don't assign initial_boot_params directly here because the
early_init_dt_scan() will do it.

The setup_vm() is supposed to setup dtb_early_va and dtb_early_pa
for MMU-enabled case so please add a "#ifdef" over there for the
built-in DTB case.

> +       else
> +               memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> +
>         /*
>          * Avoid using early_init_fdt_reserve_self() since __pa() does
>          * not work for DTB pointers that are fixmap addresses
>          */

This comment needs to be updated and moved along the memblock_reserve()
statement.

> -       memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> -
>         early_init_fdt_scan_reserved_mem();
>         dma_contiguous_reserve(dma32_phys_limit);
>         memblock_allow_resize();
> --
> 2.29.2
>

This patch should be based upon Damiens builtin DTB patch.
Refer, https://www.spinics.net/lists/linux-gpio/msg56616.html

Regards,
Anup