armstub8.S: missing ACTLR_EL3 initialization #114
Description
Currently the arm bootstub for AArch64 does not set the system register ACTLR_EL3. This register (which on reset is zero) enables access from lower exception levels to other system registers which are needed to apply fixes for errata affecting the processor. I hit this problem while working on a certain OS port to the Pi 3, however it also affects other codebases such as u-boot: https://github.com/u-boot/u-boot/blob/master/arch/arm/cpu/armv8/start.S#L208-L240
I've tested locally the following change to the armstub, and verified it working:
@@ -63,10 +63,13 @@
#define SCR_RES1_4 BIT(4)
#define SCR_NS BIT(0)
#define SCR_VAL \
(SCR_RW | SCR_HCE | SCR_SMD | SCR_RES1_5 | SCR_RES1_4 | SCR_NS)
+#define ACTLR_VAL \
+ (BIT(0) | BIT(1) | BIT(4) | BIT(5) | BIT(6))
+
#define CPUECTLR_EL1 S3_1_C15_C2_1
#define CPUECTLR_EL1_SMPEN BIT(6)
#define SPSR_EL3_D BIT(9)
#define SPSR_EL3_A BIT(8)
@@ -118,10 +121,14 @@ _start:
/* Set up SCR */
mov x0, #SCR_VAL
msr SCR_EL3, x0
+ /* Set up ACTLR */
+ mov x0, #ACTLR_VAL
+ msr ACTLR_EL3, x0
+
/* Set SMPEN */
mov x0, #CPUECTLR_EL1_SMPEN
msr CPUECTLR_EL1, x0
#ifdef GICIt would be very much appreciated if this change could make it upstream, or if an alternative solution was suggested.