GICv3: initialize without RMW

There's no need to perform an RMW sequence to initialize ICC_SRE_EL3, as
there are no bits that we need to preserve, and generally we should
reset registers to specific values such that RESx bits aren't configured
to UNKNOWN values that could be problematic in future architecture
versions.

Instead, let's initialize ICC_SRE_EL3 with a constant value. Since the
`DIB` and `DFB` fields are RAO/WI in some configurations and we have no
reason to initialize these to 0, we always initialize these to 1, in
addition to `SRE` and `SRE_Enable`.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>

3 files changed, 3 insertions, 19 deletions

diff --git a/arch/aarch32/include/asm/gic-v3.h b/arch/aarch32/include/asm/gic-v3.h
index ec9a327..65f38de 100644
--- a/arch/aarch32/include/asm/gic-v3.h
+++ b/arch/aarch32/include/asm/gic-v3.h
@@ -9,13 +9,6 @@
 #ifndef __ASM_AARCH32_GICV3_H
 #define __ASM_AARCH32_GICV3_H
 
-static inline uint32_t gic_read_icc_sre(void)
-{
-	uint32_t val;
-	asm volatile ("mrc p15, 6, %0, c12, c12, 5" : "=r" (val));
-	return val;
-}
-
 static inline void gic_write_icc_sre(uint32_t val)
 {
 	asm volatile ("mcr p15, 6, %0, c12, c12, 5" : : "r" (val));
diff --git a/arch/aarch64/include/asm/gic-v3.h b/arch/aarch64/include/asm/gic-v3.h
index e743c02..5b32380 100644
--- a/arch/aarch64/include/asm/gic-v3.h
+++ b/arch/aarch64/include/asm/gic-v3.h
@@ -15,13 +15,6 @@
 #define ICC_CTLR_EL3	"S3_6_C12_C12_4"
 #define ICC_PMR_EL1	"S3_0_C4_C6_0"
 
-static inline uint32_t gic_read_icc_sre(void)
-{
-	uint32_t val;
-	asm volatile ("mrs %0, " ICC_SRE_EL3 : "=r" (val));
-	return val;
-}
-
 static inline void gic_write_icc_sre(uint32_t val)
 {
 	asm volatile ("msr " ICC_SRE_EL3 ", %0" : : "r" (val));
diff --git a/common/gic-v3.c b/common/gic-v3.c
index 62f9676..6207007 100644
--- a/common/gic-v3.c
+++ b/common/gic-v3.c
@@ -42,6 +42,8 @@
 #define GICR_TYPER_Last			(1 << 4)
 
 #define ICC_SRE_SRE			(1 << 0)
+#define ICC_SRE_DFB			(1 << 1)
+#define ICC_SRE_DIB			(1 << 2)
 #define ICC_SRE_Enable			(1 << 3)
 
 void gic_secure_init_primary(void)
@@ -101,8 +103,6 @@ void gic_secure_init_primary(void)
 
 void gic_secure_init(void)
 {
-	uint32_t sre;
-
 	/*
 	 * If GICv3 is not available, skip initialisation. The OS will probably
 	 * fail with a warning, but this should be easier to debug than a
@@ -114,9 +114,7 @@ void gic_secure_init(void)
 	if (this_cpu_logical_id() == 0)
 		gic_secure_init_primary();
 
-	sre = gic_read_icc_sre();
-	sre |= ICC_SRE_Enable | ICC_SRE_SRE;
-	gic_write_icc_sre(sre);
+	gic_write_icc_sre(ICC_SRE_Enable | ICC_SRE_DIB | ICC_SRE_DFB | ICC_SRE_SRE);
 	isb();
 
 	gic_write_icc_ctlr(0);