linux-kernel - Re: [PATCH v2 1/7] arm64: Unconditionally call unflatten_device

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Date: Wed, 31 Jan 2024 14:54:05 -0600
From: Rob Herring <robh@...nel.org>
To: Stephen Boyd <sboyd@...nel.org>
Cc: linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
	linux-um@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
	devicetree@...r.kernel.org, Frank Rowand <frowand.list@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2 1/7] arm64: Unconditionally call
 unflatten_device_tree()

On Mon, Jan 29, 2024 at 04:45:00PM -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.
> 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@...nel.org>
> Cc: Frank Rowand <frowand.list@...il.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: <linux-arm-kernel@...ts.infradead.org>
> Signed-off-by: Stephen Boyd <sboyd@...nel.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.

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.

Rob