Re: [PATCH] arm64: Simplify checking for populated DT
From: Mark Rutland <mark.rutland@arm.com>
Date: 2021-10-29 09:38:54
Also in:
linux-devicetree
Hi Rob, On Thu, Oct 28, 2021 at 01:33:55PM -0500, Rob Herring wrote:
Use of of_scan_flat_dt() function predates libfdt and is discouraged as libfdt provides a nicer set of APIs. Rework dt_scan_depth1_nodes to use libfdt calls directly. Rather than searching for any node not /chosen or /hypervisor, let's just check for something always required which is the arch timer.
The reason for checking for /chosen and /hypervisor specifically was that we specifically permit a "stub" DT which only contains those nodes and nothing more. This is also mentioned in the comment block in acpi_boot_table_init(). I'm not keen on this change because it opens the door for people to place arbitrary things in the DT as long as they don't add a timer node, and I'd prefer that we continue to check for /chosen and /hypervisor specifically. Can we re-implement the existing logic using libfdt calls? e.g. using fdt_for_each_subnode() on the root node? Thanks, Mark.
quoted hunk ↗ jump to hunk
Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Rob Herring <robh@kernel.org> --- arch/arm64/kernel/acpi.c | 29 ++++++----------------------- 1 file changed, 6 insertions(+), 23 deletions(-)diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c index 1c9c2f7a1c04..f1bb0fb4a604 100644 --- a/arch/arm64/kernel/acpi.c +++ b/arch/arm64/kernel/acpi.c@@ -22,6 +22,7 @@ #include <linux/irq_work.h> #include <linux/memblock.h> #include <linux/of_fdt.h> +#include <linux/libfdt.h> #include <linux/smp.h> #include <linux/serial_core.h> #include <linux/pgtable.h>@@ -62,29 +63,12 @@ static int __init parse_acpi(char *arg) } early_param("acpi", parse_acpi); -static int __init dt_scan_depth1_nodes(unsigned long node, - const char *uname, int depth, - void *data) +static bool __init dt_is_populated(void) { - /* - * Ignore anything not directly under the root node; we'll - * catch its parent instead. - */ - if (depth != 1) - return 0; - - if (strcmp(uname, "chosen") == 0) - return 0; + const void *fdt = initial_boot_params; + int node = fdt_node_offset_by_compatible(fdt, -1, "arm,armv8-timer"); - if (strcmp(uname, "hypervisor") == 0 && - of_flat_dt_is_compatible(node, "xen,xen")) - return 0; - - /* - * This node at depth 1 is neither a chosen node nor a xen node, - * which we do not expect. - */ - return 1; + return node > 0 ? true : false; } /*@@ -205,8 +189,7 @@ void __init acpi_boot_table_init(void) * and ACPI has not been [force] enabled (acpi=on|force) */ if (param_acpi_off || - (!param_acpi_on && !param_acpi_force && - of_scan_flat_dt(dt_scan_depth1_nodes, NULL))) + (!param_acpi_on && !param_acpi_force && dt_is_populated())) goto done; /*-- 2.32.0
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