Enable asynchronous abort exceptions during boot

Asynchronous abort exceptions generated by the platform during cold boot are
not taken in EL3 unless SCR_EL3.EA is set.

Therefore EA bit is set along with RES1 bits in early BL1 and BL31 architecture
initialisation. Further write accesses to SCR_EL3 preserve these bits during
cold boot.

A build flag controls SCR_EL3.EA value to keep asynchronous abort exceptions
being trapped by EL3 after cold boot or not.

For further reference SError Interrupts are also known as asynchronous external
aborts.

On Cortex-A53 revisions below r0p2, asynchronous abort exceptions are taken in
EL3 whatever the SCR_EL3.EA value is.

Fixes arm-software/tf-issues#368

Signed-off-by: Gerald Lejeune <gerald.lejeune@st.com>

6 files changed, 21 insertions, 8 deletions

diff --git a/bl1/aarch64/bl1_arch_setup.c b/bl1/aarch64/bl1_arch_setup.c
index 6a3f0623..61c01e19 100644
--- a/bl1/aarch64/bl1_arch_setup.c
+++ b/bl1/aarch64/bl1_arch_setup.c
@@ -38,7 +38,7 @@
 void bl1_arch_setup(void)
 {
 	/* Set the next EL to be AArch64 */
-	write_scr_el3(SCR_RES1_BITS | SCR_RW_BIT);
+	write_scr_el3(read_scr_el3() | SCR_RW_BIT);
 }
 
 /*******************************************************************************
diff --git a/bl31/aarch64/bl31_arch_setup.c b/bl31/aarch64/bl31_arch_setup.c
index edf10188..0871b419 100644
--- a/bl31/aarch64/bl31_arch_setup.c
+++ b/bl31/aarch64/bl31_arch_setup.c
@@ -43,9 +43,6 @@
  ******************************************************************************/
 void bl31_arch_setup(void)
 {
-	/* Set the RES1 bits in the SCR_EL3 */
-	write_scr_el3(SCR_RES1_BITS);
-
 	/* Program the counter frequency */
 	write_cntfrq_el0(plat_get_syscnt_freq());
 
diff --git a/common/context_mgmt.c b/common/context_mgmt.c
index 68ec8945..586d42a4 100644
--- a/common/context_mgmt.c
+++ b/common/context_mgmt.c
@@ -111,6 +111,11 @@ static void cm_init_context_common(cpu_context_t *ctx, const entry_point_info_t
 	if (EP_GET_ST(ep->h.attr))
 		scr_el3 |= SCR_ST_BIT;
 
+#ifndef HANDLE_EA_EL3_FIRST
+	/* Explicitly stop to trap aborts from lower exception levels. */
+	scr_el3 &= ~SCR_EA_BIT;
+#endif
+
 #if IMAGE_BL31
 	/*
 	 * IRQ/FIQ bits only need setting if interrupt routing
diff --git a/docs/firmware-design.md b/docs/firmware-design.md
index 54c50680..fe3c3f03 100644
--- a/docs/firmware-design.md
+++ b/docs/firmware-design.md
@@ -174,8 +174,9 @@ BL1 performs minimal architectural initialization as follows.
         `SCTLR_EL3.A` and `SCTLR_EL3.SA` bits. Exception endianness is set to
         little-endian by clearing the `SCTLR_EL3.EE` bit.
 
-    -  `SCR_EL3`. The register width of the next lower exception level is set to
-        AArch64 by setting the `SCR.RW` bit.
+    -  `SCR_EL3`. The register width of the next lower exception level is set
+        to AArch64 by setting the `SCR.RW` bit. The `SCR.EA` bit is set to trap
+        both External Aborts and SError Interrupts in EL3.
 
     -   `CPTR_EL3`. Accesses to the `CPACR_EL1` register from EL1 or EL2, or the
         `CPTR_EL2` register from EL2 are configured to not trap to EL3 by
diff --git a/docs/user-guide.md b/docs/user-guide.md
index ea10a81e..315e7468 100644
--- a/docs/user-guide.md
+++ b/docs/user-guide.md
@@ -439,6 +439,9 @@ performed.
     where applicable). Defaults to a string that contains the time and date of
     the compilation.
 
+*   `HANDLE_EA_EL3_FIRST`: When defined External Aborts and SError Interrupts
+    will be always trapped in EL3 i.e. in BL31 at runtime.
+
 #### ARM development platform specific build options
 
 *   `ARM_TSP_RAM_LOCATION`: location of the TSP binary. Options:
diff --git a/include/common/el3_common_macros.S b/include/common/el3_common_macros.S
index 0cd85c34..ba80d95d 100644
--- a/include/common/el3_common_macros.S
+++ b/include/common/el3_common_macros.S
@@ -70,8 +70,15 @@
 	isb
 
 	/* ---------------------------------------------------------------------
-	 * Enable the SError interrupt now that the exception vectors have been
-	 * setup.
+	 * Early set RES1 bits in SCR_EL3. Set EA bit as well to catch both
+	 * External Aborts and SError Interrupts in EL3.
+	 * ---------------------------------------------------------------------
+	 */
+	mov	x0, #(SCR_RES1_BITS | SCR_EA_BIT)
+	msr	scr_el3, x0
+	/* ---------------------------------------------------------------------
+	 * Enable External Aborts and SError Interrupts now that the exception
+	 * vectors have been setup.
 	 * ---------------------------------------------------------------------
 	 */
 	msr	daifclr, #DAIF_ABT_BIT