On Thu, Dec 31, 2020 at 3:23 PM Vitaly Wool [off-list ref] wrote:

On Tue, Dec 29, 2020 at 6:05 AM Anup Patel [off-list ref] wrote:

quoted

On Mon, Dec 28, 2020 at 10:08 PM Vitaly Wool [off-list ref] wrote:

quoted

On Mon, Dec 28, 2020 at 3:10 PM Anup Patel [off-list ref] wrote:

quoted

On Mon, Dec 28, 2020 at 7:05 PM Vitaly Wool [off-list ref] wrote:

quoted

On Mon, Dec 28, 2020 at 12:59 PM Anup Patel [off-list ref] wrote:

quoted

On Sat, Dec 26, 2020 at 10:03 PM Vitaly Wool [off-list ref] wrote:

quoted

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 <redacted>
---
 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.

I might be out in the woods here but... Do you mean the call to
early_init_dt_verify() in setup_arch() which is compiled out
completely in the CONFIG_BUILTIN_DTB case?
Or is there any other call that I'm overlooking?

Sorry for the confusion, what I meant was that we are calling
early_init_dt_verify() from setup_arch() for the MMU-enabled
with built-in DTB disabled case to update "initial_boot_params"
after the boot CPU has switched from early_pg_dir to swapper_pg_dir.

For MMU-enabled with built-in DTB case, if setup_vm() sets the
dtb_early_va and dtb_early_pa correctly then early_init_dt_scan()
called from setup_arch() will automatically set correct value for
"initial_boot_params".

Oh I think I get it now. You are suggesting to skip the temporary
mapping for DT altogether since it is anyway in the kernel mapping
range, aren't you?
That does make sense indeed, thanks :)

Yes, that's what I am suggesting.

quoted

It is strange that early_init_dt_verify() is being compiled-out for you
because the early_init_dt_scan() called from setup_arch() also uses
early_init_dt_verify(). I quickly compiled the NoMMU kernel for K210
which also uses built-in DTB and I see that early_init_dt_verify()
is not being compiled-out when built-in DTB is enabled.

I did not say that early_init_dt_verify() is compiled out, it's the
call to it in setup_arch() that is compiled out if BUILTIN_DTB is
selected. However, if I understand you correctly now, it should not
matter if we don't set dtb_early_va to point to the temporary mapping.

Yes, dtb_early_va can point to some other location such as
built-in DTB.

For MMU-enabled with built-in DTB case, the setup_vm() should
skip the temporary mapping to DT and instead set dtb_early_va
and dtb_early_pa to point to the built-in DTB.

Regards,
Anup