On Fri, Feb 23, 2024 at 11:17:02AM -0700, Rob Herring wrote:
On Fri, Feb 23, 2024 at 3:23 AM Will Deacon will@kernel.org wrote:
On Thu, Feb 22, 2024 at 05:03:17PM -0700, Rob Herring wrote:
On Fri, Feb 16, 2024 at 05:05:54PM -0800, Stephen Boyd wrote:
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. When ACPI is in use, unflatten_device_tree() ignores the 'initial_boot_params' pointer so the live DT on those systems won't be whatever that's pointing to. Similarly, when kexec copies the DT data the previous kernel to the new one on ACPI systems, of_kexec_alloc_and_setup_fdt() will ignore the live DT (the empty root one) and copy the 'initial_boot_params' data.
Cc: Rob Herring robh+dt@kernel.org Cc: Frank Rowand frowand.list@gmail.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Stephen Boyd sboyd@kernel.org
arch/arm64/kernel/setup.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
Catalin, Will, Can I get an ack on this so I can take the series via the DT tree.
Mark had strong pretty strong objections to this in version one:
Yes, I had concerns with it as well.
https://lore.kernel.org/all/ZaZtbU9hre3YhZam@FVFF77S0Q05N/
and this patch looks the same now as it did then. Did something else change?
Yes, that version unflattened the bootloader passed DT. Now within unflatten_devicetree(), the bootloader DT is ignored if ACPI is enabled and we unflatten an empty tree. That will prevent the kernel getting 2 h/w descriptions if/when a platform does such a thing. Also, kexec still uses the bootloader provided DT as before.
That avoids the main instance of my concern, and means that this'll boot without issue, but IIUC this opens the door to dynamically instantiating DT devices atop an ACPI base system, which I think in general is something that's liable to cause more problems than it solves.
I understand that's desireable for the selftests, though I still don't believe it's strictly necessary -- there are plenty of other things that only work if the kernel is booted in a specific configuration.
Putting the selftests aside, why do we need to do this? Is there any other reason to enable this?
Mark.