On 27.02.22 14:07, Mark Kettenis wrote:
From: Alexander Graf <ag...@csgraf.de>
Date: Sun, 27 Feb 2022 13:18:56 +0100

For targets that enable ACPI, we should not pass Device Trees into
the payload. However, our distro boot logic always passes the builtin
DT as an argument.

To make it easy to use ACPI with distro boot, let's just ignore the DT
argument to bootefi when ACPI is enabled. That way, we can successfully
distro boot payloads on ACPI enabled targets.
I've never understood why it is bad to provide both the DT and ACPI
tables.  Several TianoCore EDK2 based firmwares do this or at least
give you the option to do this.  And it works fine.  If both are
provided, you just leave it up to the OS to decide what it wants to
use.  Which makes me think the text was put there in the standard by
people with an agenda...


It's much more profane :). Upstream Linux went with "DT first, ACPI last" while RHEL had a downstream patch that went "ACPI first, DT last". And then people were confused why RHEL and upstream kernels had such vastly different behavior on their systems.

Long story short, the best way to avoid this ambiguity is to only provide one of the 2 to the OS. And that's what the BBRs dictate now. They don't dictate what firmware does internally though, so we're free to do whatever we like - and I think "if someone went through the effort to enable ACPI on this system, they probably want to use it" is a fair assumption with U-Boot. So we should prefer ACPI if available.


Alex



I think it would be good for U-Boot to give users a choice here, with
all possible combinations (only DT, only ACPI, both DT and ACPI).  But
this is a step in the right direction.

Reviewed-by: Mark Kettenis <kette...@openbsd.org>

Signed-off-by: Alexander Graf <ag...@csgraf.de>
---
  cmd/bootefi.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cmd/bootefi.c b/cmd/bootefi.c
index 94d18ca73f..2c9bc0dcd2 100644
--- a/cmd/bootefi.c
+++ b/cmd/bootefi.c
@@ -265,8 +265,8 @@ efi_status_t efi_install_fdt(void *fdt)
         */
  #if CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)
        if (fdt) {
-               log_err("ERROR: can't have ACPI table and device tree.\n");
-               return EFI_LOAD_ERROR;
+               log_warning("WARNING: Can't have ACPI table and device tree - 
ignoring DT.\n");
+               return EFI_SUCCESS;
        }
  #else
        bootm_headers_t img = { 0 };
--
2.32.0


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