armv8: Initialize CNTFRQ if at highest exception level
CNTFRQ_EL0 is only writable from the highest supported exception
level on the platform. For Armv8-A, this is typically EL3, but
technically EL2 and EL3 are optional so it may need to be
initialized at EL2 or EL1. For Armv8-R, the highest exception
level is always EL2.
This patch moves the initialization outside of the switch_el
block and uses a new macro branch_if_not_highest_el which
dynamically detects whether it is at the highest supported
exception level.
Linux's docs state that CNTFRQ_EL0 should be initialized by the
bootloader. If not set, the the U-Boot prompt countdown hangs.
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
index 9e9c614..b3eef70 100644
--- a/arch/arm/cpu/armv8/start.S
+++ b/arch/arm/cpu/armv8/start.S
@@ -127,10 +127,6 @@
orr x0, x0, #0xf /* SCR_EL3.NS|IRQ|FIQ|EA */
msr scr_el3, x0
msr cptr_el3, xzr /* Enable FP/SIMD */
-#ifdef COUNTER_FREQUENCY
- ldr x0, =COUNTER_FREQUENCY
- msr cntfrq_el0, x0 /* Initialize CNTFRQ */
-#endif
b 0f
2: mrs x1, hcr_el2
tbnz x1, #34, 1f /* HCR_EL2.E2H */
@@ -142,7 +138,14 @@
mov x0, #3 << 20
msr cpacr_el1, x0 /* Enable FP/SIMD */
0:
- isb
+
+#ifdef COUNTER_FREQUENCY
+ branch_if_not_highest_el x0, 4f
+ ldr x0, =COUNTER_FREQUENCY
+ msr cntfrq_el0, x0 /* Initialize CNTFRQ */
+#endif
+
+4: isb
/*
* Enable SMPEN bit for coherency.
diff --git a/arch/arm/include/asm/macro.h b/arch/arm/include/asm/macro.h
index bb33b4b..485310d 100644
--- a/arch/arm/include/asm/macro.h
+++ b/arch/arm/include/asm/macro.h
@@ -78,6 +78,24 @@
.endm
/*
+ * Branch if we are not in the highest exception level
+ */
+.macro branch_if_not_highest_el, xreg, label
+ switch_el \xreg, 3f, 2f, 1f
+
+2: mrs \xreg, ID_AA64PFR0_EL1
+ and \xreg, \xreg, #(ID_AA64PFR0_EL1_EL3)
+ cbnz \xreg, \label
+ b 3f
+
+1: mrs \xreg, ID_AA64PFR0_EL1
+ and \xreg, \xreg, #(ID_AA64PFR0_EL1_EL3 | ID_AA64PFR0_EL1_EL2)
+ cbnz \xreg, \label
+
+3:
+.endm
+
+/*
* Branch if current processor is a Cortex-A57 core.
*/
.macro branch_if_a57_core, xreg, a57_label
diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index 11fceec..8b3a54e 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -80,6 +80,12 @@
#define HCR_EL2_HCD_DIS (1 << 29) /* Hypervisor Call disabled */
/*
+ * ID_AA64PFR0_EL1 bits definitions
+ */
+#define ID_AA64PFR0_EL1_EL3 (0xF << 12) /* EL3 implemented */
+#define ID_AA64PFR0_EL1_EL2 (0xF << 8) /* EL2 implemented */
+
+/*
* CPACR_EL1 bits definitions
*/
#define CPACR_EL1_FPEN_EN (3 << 20) /* SIMD and FP instruction enabled */