Nicholas Piggin <npig...@gmail.com> writes:
> Provide a dt_cpu_ftrs= cmdline option to disable the dt_cpu_ftrs CPU
> feature discovery, and fall back to the "cputable" based version.
I don't think this works properly.
> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c
> b/arch/powerpc/kernel/dt_cpu_ftrs.c
> index fcc7588a96d6..050925b5b451 100644
> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> @@ -775,6 +785,16 @@ bool __init dt_cpu_ftrs_in_use(void)
>
> bool __init dt_cpu_ftrs_init(void *fdt)
> {
> + if (!using_dt_cpu_ftrs) {
> + /*
> + * This should never happen because this runs before
> + * early_praam, however if the init ordering changes,
> + * test if early_param has disabled this.
> + */
> + return false;
> + }
> + using_dt_cpu_ftrs = false;
> +
> /* Setup and verify the FDT, if it fails we just bail */
> if (!early_init_dt_verify(fdt))
> return false;
...
return true;
Because this runs before early_param(), as you mention,
dt_cpu_ftrs_init() returns true, which means we skip calling
identify_cpu().
So although passing dt_cpu_ftrs=off will skip the later logic, it
doesn't cause us to call identify_cpu() in early_setup() which it
should.
In practice it works because the base CPU spec that we initialise in
dt_cpu_ftrs.c is mostly OK, and skiboot also adds the cpu-version
property which causes us to call identify_cpu() again later, but that's
all a bit fragile IMHO.
So unfortunately I think we need to add logic in dt_cpu_ftrs_init() to
look for dt_cpu_ftrs=off on the command line.
The patch below seems to work, but would appreciate more eyes on it.
cheers
diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c
b/arch/powerpc/kernel/dt_cpu_ftrs.c
index d6f05e4dc328..9a560954498a 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -8,6 +8,7 @@
#include <linux/export.h>
#include <linux/init.h>
#include <linux/jump_label.h>
+#include <linux/libfdt.h>
#include <linux/memblock.h>
#include <linux/printk.h>
#include <linux/sched.h>
@@ -767,6 +770,26 @@ static void __init cpufeatures_setup_finished(void)
cur_cpu_spec->cpu_features, cur_cpu_spec->mmu_features);
}
+static int __init disabled_on_cmdline(void)
+{
+ unsigned long root, chosen;
+ const char *p;
+
+ root = of_get_flat_dt_root();
+ chosen = of_get_flat_dt_subnode_by_name(root, "chosen");
+ if (chosen == -FDT_ERR_NOTFOUND)
+ return false;
+
+ p = of_get_flat_dt_prop(chosen, "bootargs", NULL);
+ if (!p)
+ return false;
+
+ if (strstr(p, "dt_cpu_ftrs=off"))
+ return true;
+
+ return false;
+}
+
static int __init fdt_find_cpu_features(unsigned long node, const char *uname,
int depth, void *data)
{
@@ -801,6 +826,9 @@ bool __init dt_cpu_ftrs_init(void *fdt)
if (!of_scan_flat_dt(fdt_find_cpu_features, NULL))
return false;
+ if (disabled_on_cmdline())
+ return false;
+
cpufeatures_setup_cpu();
using_dt_cpu_ftrs = true;
