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

[Vitaly Wool]

On Mon, Dec 28, 2020 at 12:59 PM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
>
> 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.

early_init_dt_scan will set initial_boot_params to dtb_early_va from
the early mapping which will be gone by the time
unflatten_and_copy_device_tree() is called.

> 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

Thanks for the pointer, however I don't think our patches have
intersections. Besides, Damien is dealing with the MMU-less case
there.

Best regards,
   Vitaly