Add build configuration for timer save/restore
At present, non-secure timer register contents are saved and restored as
part of world switch by BL3-1. This effectively means that the
non-secure timer stops, and non-secure timer interrupts are prevented
from asserting until BL3-1 switches back, introducing latency for
non-secure services. Often, secure world might depend on alternate
sources for secure interrupts (secure timer or platform timer) instead
of non-secure timers, in which case this save and restore is
unnecessary.
This patch introduces a boolean build-time configuration NS_TIMER_SWITCH
to choose whether or not to save and restore non-secure timer registers
upon world switch. The default choice is made not to save and restore
them.
Fixes ARM-software/tf-issues#148
Change-Id: I1b9d623606acb9797c3e0b02fb5ec7c0a414f37e
diff --git a/Makefile b/Makefile
index fc6c469..94dde7f 100644
--- a/Makefile
+++ b/Makefile
@@ -45,6 +45,8 @@
SPD := none
# Base commit to perform code check on
BASE_COMMIT := origin/master
+# NS timer register save and restore
+NS_TIMER_SWITCH := 0
# Checkpatch ignores
@@ -171,6 +173,10 @@
ASFLAGS += -g -Wa,--gdwarf-2
endif
+# Process NS_TIMER_SWITCH flag
+$(eval $(call assert_boolean,NS_TIMER_SWITCH))
+$(eval $(call add_define,NS_TIMER_SWITCH))
+
ASFLAGS += -nostdinc -ffreestanding -Wa,--fatal-warnings \
-mgeneral-regs-only -D__ASSEMBLY__ \
${DEFINES} ${INCLUDES}
diff --git a/bl31/aarch64/context.S b/bl31/aarch64/context.S
index 45d4a22..d0bca64 100644
--- a/bl31/aarch64/context.S
+++ b/bl31/aarch64/context.S
@@ -172,6 +172,8 @@
mrs x9, vbar_el1
stp x17, x9, [x0, #CTX_CONTEXTIDR_EL1]
+ /* Save NS timer registers if the build has instructed so */
+#if NS_TIMER_SWITCH
mrs x10, cntp_ctl_el0
mrs x11, cntp_cval_el0
stp x10, x11, [x0, #CTX_CNTP_CTL_EL0]
@@ -181,8 +183,11 @@
stp x12, x13, [x0, #CTX_CNTV_CTL_EL0]
mrs x14, cntkctl_el1
+ str x14, [x0, #CTX_CNTKCTL_EL1]
+#endif
+
mrs x15, fpexc32_el2
- stp x14, x15, [x0, #CTX_CNTKCTL_EL1]
+ str x15, [x0, #CTX_FP_FPEXC32_EL2]
ret
@@ -253,6 +258,8 @@
msr contextidr_el1, x17
msr vbar_el1, x9
+ /* Restore NS timer registers if the build has instructed so */
+#if NS_TIMER_SWITCH
ldp x10, x11, [x0, #CTX_CNTP_CTL_EL0]
msr cntp_ctl_el0, x10
msr cntp_cval_el0, x11
@@ -261,8 +268,11 @@
msr cntv_ctl_el0, x12
msr cntv_cval_el0, x13
- ldp x14, x15, [x0, #CTX_CNTKCTL_EL1]
+ ldr x14, [x0, #CTX_CNTKCTL_EL1]
msr cntkctl_el1, x14
+#endif
+
+ ldr x15, [x0, #CTX_FP_FPEXC32_EL2]
msr fpexc32_el2, x15
/* No explict ISB required here as ERET covers it */
diff --git a/docs/user-guide.md b/docs/user-guide.md
index edf03f0..e7f0df5 100644
--- a/docs/user-guide.md
+++ b/docs/user-guide.md
@@ -141,6 +141,11 @@
* `DEBUG`: Chooses between a debug and release build. It can take either 0
(release) or 1 (debug) as values. 0 is the default
+* `NS_TIMER_SWITCH`: Enable save and restore for non-secure timer register
+ contents upon world switch. It can take either 0 (don't save and restore) or
+ 1 (do save and restore). 0 is the default. An SPD could set this to 1 if it
+ wants the timer registers to be saved and restored
+
* `PLAT`: Choose a platform to build ARM Trusted Firmware for. The chosen
platform name must be the name of one of the directories under the `plat/`
directory other than `common`
diff --git a/include/bl31/context.h b/include/bl31/context.h
index 549fa21..b0dfec1 100644
--- a/include/bl31/context.h
+++ b/include/bl31/context.h
@@ -127,6 +127,11 @@
#define CTX_AFSR1_EL1 0xc8
#define CTX_CONTEXTIDR_EL1 0xd0
#define CTX_VBAR_EL1 0xd8
+/*
+ * If the timer registers aren't saved and restored, we don't have to reserve
+ * space for them in the context
+ */
+#if NS_TIMER_SWITCH
#define CTX_CNTP_CTL_EL0 0xe0
#define CTX_CNTP_CVAL_EL0 0xe8
#define CTX_CNTV_CTL_EL0 0xf0
@@ -134,6 +139,10 @@
#define CTX_CNTKCTL_EL1 0x100
#define CTX_FP_FPEXC32_EL2 0x108
#define CTX_SYSREGS_END 0x110
+#else
+#define CTX_FP_FPEXC32_EL2 0xe0
+#define CTX_SYSREGS_END 0xf0
+#endif
/*******************************************************************************
* Constants that allow assembler code to access members of and the 'fp_regs'