powerpc/mm/radix: Add a kernel command line to disable radix

This patch adds the kernel command line disable_radix which disable
the radix MMU mode even if firmware indicates radix support via
ibm,pa-features device tree node.

This helps in testing different MMU mode easily.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 738bae4..bba7ef3 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -929,6 +929,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
        disable=        [IPV6]
                        See Documentation/networking/ipv6.txt.
 
+       disable_radix   [PPC]
+                       Disable RADIX MMU mode on POWER9
+
        disable_cpu_apicid= [X86,APIC,SMP]
                        Format: <int>
                        The number of initial APIC ID for the

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 48434be..7a01113 100644 (file)
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -646,6 +646,14 @@ static void __init early_reserve_mem(void)
 #endif
 }
 
+static bool disable_radix;
+static int __init parse_disable_radix(char *p)
+{
+       disable_radix = true;
+       return 0;
+}
+early_param("disable_radix", parse_disable_radix);
+
 void __init early_init_devtree(void *params)
 {
        phys_addr_t limit;
@@ -735,6 +743,11 @@ void __init early_init_devtree(void *params)
         */
        spinning_secondaries = boot_cpu_count - 1;
 #endif
+       /*
+        * now fixup radix MMU mode based on kernel command line
+        */
+       if (disable_radix)
+               cur_cpu_spec->mmu_features &= ~MMU_FTR_RADIX;
 
 #ifdef CONFIG_PPC_POWERNV
        /* Scan and build the list of machine check recoverable ranges */