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

[Anup Patel <anup@brainfault.org>]

On Mon, Dec 28, 2020 at 7:05 PM Vitaly Wool <vitaly.wool@konsulko.com> wrote:
>
> On Mon, Dec 28, 2020 at 12:59 PM Anup Patel <anup@brainfault.org> wrote:
> >
> > On Sat, Dec 26, 2020 at 10:03 PM Vitaly Wool <vitaly.wool@konsulko.com> 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@konsulko.com>
> > > ---
> > >  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.

That's why we are doing early_init_dt_verify() again for the MMU-enabled
case which already takes care of your concern.

We use early_init_dt_verify() like most architectures to set the initial DTB.

>
> > 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.

Damien's patch is also trying to move to use generic BUILTIN_DTB
support for the MMU-less case so it is similar work hence the chance
of patch conflict.

Regards,
Anup