Currently ppc_md.get_random_seed uses the powernv_get_random_long function.
A guest calling this function would have to go through the hypervisor. The
'darn' instruction, introduced in POWER9, allows us to bypass this by
directly obtaining a value from the mmio region.
This patch adds a function for ppc_md.get_random_seed on p9,
utilising the darn instruction.
Signed-off-by: Matt Brown <matthew.brown....@gmail.com>
---
v2:
- remove repeat darn attempts
- move hook to rng_init
---
arch/powerpc/include/asm/ppc-opcode.h | 4 ++++
arch/powerpc/platforms/powernv/rng.c | 22 ++++++++++++++++++++++
2 files changed, 26 insertions(+)
diff --git a/arch/powerpc/include/asm/ppc-opcode.h
b/arch/powerpc/include/asm/ppc-opcode.h
index c4ced1d..d5f7082 100644
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h
@@ -134,6 +134,7 @@
#define PPC_INST_COPY 0x7c00060c
#define PPC_INST_COPY_FIRST 0x7c20060c
#define PPC_INST_CP_ABORT 0x7c00068c
+#define PPC_INST_DARN 0x7c0005e6
#define PPC_INST_DCBA 0x7c0005ec
#define PPC_INST_DCBA_MASK 0xfc0007fe
#define PPC_INST_DCBAL 0x7c2005ec
@@ -325,6 +326,9 @@
/* Deal with instructions that older assemblers aren't aware of */
#define PPC_CP_ABORT stringify_in_c(.long PPC_INST_CP_ABORT)
+#define PPC_DARN(t, l) stringify_in_c(.long PPC_INST_DARN | \
+ ___PPC_RT(t) | \
+ ___PPC_RA(l))
#define PPC_DCBAL(a, b) stringify_in_c(.long PPC_INST_DCBAL | \
__PPC_RA(a) | __PPC_RB(b))
#define PPC_DCBZL(a, b) stringify_in_c(.long PPC_INST_DCBZL | \
diff --git a/arch/powerpc/platforms/powernv/rng.c
b/arch/powerpc/platforms/powernv/rng.c
index 5dcbdea..ab6f411 100644
--- a/arch/powerpc/platforms/powernv/rng.c
+++ b/arch/powerpc/platforms/powernv/rng.c
@@ -8,6 +8,7 @@
*/
#define pr_fmt(fmt) "powernv-rng: " fmt
+#define DARN_ERR 0xFFFFFFFFFFFFFFFFul
#include <linux/kernel.h>
#include <linux/of.h>
@@ -16,6 +17,7 @@
#include <linux/slab.h>
#include <linux/smp.h>
#include <asm/archrandom.h>
+#include <asm/cputable.h>
#include <asm/io.h>
#include <asm/prom.h>
#include <asm/machdep.h>
@@ -67,6 +69,21 @@ int powernv_get_random_real_mode(unsigned long *v)
return 1;
}
+int powernv_get_random_darn(unsigned long *v)
+{
+ unsigned long val;
+
+ /* Using DARN with L=1 - conditioned random number */
+ asm (PPC_DARN(%0, 1)"\n" : "=r"(val) :);
+
+ if (val == DARN_ERR)
+ return 0;
+
+ *v = val;
+
+ return 1;
+}
+
int powernv_get_random_long(unsigned long *v)
{
struct powernv_rng *rng;
@@ -136,6 +153,7 @@ static __init int rng_create(struct device_node *dn)
static __init int rng_init(void)
{
struct device_node *dn;
+ unsigned long drn_test;
int rc;
for_each_compatible_node(dn, NULL, "ibm,power-rng") {
@@ -150,6 +168,10 @@ static __init int rng_init(void)
of_platform_device_create(dn, NULL, NULL);
}
+ if (cpu_has_feature(CPU_FTR_ARCH_300) &&
+ powernv_get_random_darn(&drn_test))
+ ppc_md.get_random_seed = powernv_get_random_darn;
+
return 0;
}
machine_subsys_initcall(powernv, rng_init);
--
2.9.3
