Quoting Rob Herring (2024-01-31 12:54:05)

On Mon, Jan 29, 2024 at 04:45:00PM -0800, Stephen Boyd wrote:

quoted

Call this function unconditionally so that we can populate an empty DTB
on platforms that don't boot with a firmware provided or builtin DTB.
Override 'initial_boot_params' to NULL when ACPI is in use but the
bootloader has loaded a DTB so that we don't allow both ACPI and DT to
be used during boot. If there isn't a valid initial_boot_params dtb then
unflatten_device_tree() returns early so this is fine.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: <redacted>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
---
 arch/arm64/kernel/setup.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 417a8a86b2db..ffb1942724ae 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c

@@ -351,8 +351,11 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
      /* Parse the ACPI tables for possible boot-time configuration */
      acpi_boot_table_init();
 
-     if (acpi_disabled)
-             unflatten_device_tree();
+     /* Don't use the FDT from boot if ACPI is in use */
+     if (!acpi_disabled)
+             initial_boot_params = NULL;

I still think this is a problem for kexec. See 
of_kexec_alloc_and_setup_fdt(). You see it uses initial_boot_params. At 
first glance it looks like it would just write out everything we need. 
But for UEFI boot, I think we need all the chosen properties like 
linux,uefi-mmap-start preserved from the current boot for the next 
kernel we kexec.

Ok, got it.

I think you'll have to check acpi_disabled in unflatten_device_tree() 
and unflatten the empty tree leaving initial_boot_params alone. That 
means our FDT and unflattened tree will be different DTs, but I think 
that's fine.

It's sort of scary given that 'initial_boot_params' is an exported
global. Maybe that should be hidden away and accessed with a function
instead so that this mismatch doesn't break something later on?

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