feat(cpufeat): enable FEAT_SVE for FEAT_STATE_CHECKED

Add support for runtime detection (ENABLE_SVE_FOR_NS=2), by splitting
sve_supported() into an ID register reading function and a
second function to report the support status. That function considers
both build time settings and runtime information (if needed), and is
used before we do SVE specific setup.

Change the FVP platform default to the now supported dynamic
option (=2), so the right decision can be made by the code at runtime.

Change-Id: I1caaba2216e8e2a651452254944a003607503216
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>

12 files changed, 76 insertions, 86 deletions

diff --git a/Makefile b/Makefile
index 20b2aa296..d2427227c 100644
--- a/Makefile
+++ b/Makefile
@@ -1106,7 +1106,6 @@ $(eval $(call assert_booleans,\
         ENABLE_PSCI_STAT \
         ENABLE_RUNTIME_INSTRUMENTATION \
         ENABLE_SME_FOR_SWD \
-        ENABLE_SVE_FOR_NS \
         ENABLE_SVE_FOR_SWD \
         ERROR_DEPRECATED \
         FAULT_INJECTION_SUPPORT \
@@ -1193,6 +1192,7 @@ $(eval $(call assert_numerics,\
         ENABLE_SPE_FOR_NS \
         ENABLE_SYS_REG_TRACE_FOR_NS \
         ENABLE_SME_FOR_NS \
+        ENABLE_SVE_FOR_NS \
         ENABLE_TRF_FOR_NS \
         FW_ENC_STATUS \
         NR_OF_FW_BANKS \
diff --git a/bl31/bl31.mk b/bl31/bl31.mk
index 8f3725ad5..4d151ab45 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -103,7 +103,7 @@ ifneq (${ENABLE_SME_FOR_NS},0)
 BL31_SOURCES		+=	lib/extensions/sme/sme.c
 BL31_SOURCES		+=	lib/extensions/sve/sve.c
 else
-ifeq (${ENABLE_SVE_FOR_NS},1)
+ifneq (${ENABLE_SVE_FOR_NS},0)
 BL31_SOURCES		+=	lib/extensions/sve/sve.c
 endif
 endif
diff --git a/common/feat_detect.c b/common/feat_detect.c
index 609a38888..9394304bf 100644
--- a/common/feat_detect.c
+++ b/common/feat_detect.c
@@ -171,6 +171,8 @@ void detect_arch_features(void)
 
 	/* v8.2 features */
 	read_feat_ras();
+	check_feature(ENABLE_SVE_FOR_NS, read_feat_sve_id_field(),
+		      "SVE", 1, 1);
 
 	/* v8.3 features */
 	read_feat_pauth();
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 4483dd424..1ee07d9ac 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -428,7 +428,7 @@ Common build options
    mechanism. The default is 2 but is automatically disabled when the target
    architecture is AArch32.
 
--  ``ENABLE_SVE_FOR_NS``: Boolean option to enable Scalable Vector Extension
+-  ``ENABLE_SVE_FOR_NS``: Numeric value to enable Scalable Vector Extension
    (SVE) for the Non-secure world only. SVE is an optional architectural feature
    for AArch64. Note that when SVE is enabled for the Non-secure world, access
    to SIMD and floating-point functionality from the Secure world is disabled by
@@ -437,9 +437,10 @@ Common build options
    which are aliased by the SIMD and FP registers. The build option is not
    compatible with the ``CTX_INCLUDE_FPREGS`` build option, and will raise an
    assert on platforms where SVE is implemented and ``ENABLE_SVE_FOR_NS`` set to
-   1. The default is 1 but is automatically disabled when ENABLE_SME_FOR_NS=1
-   since SME encompasses SVE. At this time, this build option cannot be used on
-   systems that have SPM_MM enabled.
+   1. This flag can take the values 0 to 2, to align with the ``FEATURE_DETECTION``
+   mechanism. The default is 1 but is automatically disabled when
+   ENABLE_SME_FOR_NS=1 since SME encompasses SVE. At this time, this build
+   option cannot be used on systems that have SPM_MM enabled.
 
 -  ``ENABLE_SVE_FOR_SWD``: Boolean option to enable SVE for the Secure world.
    SVE is an optional architectural feature for AArch64. Note that this option
diff --git a/include/arch/aarch64/arch_features.h b/include/arch/aarch64/arch_features.h
index a01dfe783..3ea08a665 100644
--- a/include/arch/aarch64/arch_features.h
+++ b/include/arch/aarch64/arch_features.h
@@ -387,10 +387,22 @@ static inline bool is_feat_spe_supported(void)
 /*******************************************************************************
  * Function to identify the presence of FEAT_SVE (Scalable Vector Extension)
  ******************************************************************************/
-static inline bool is_armv8_2_feat_sve_present(void)
+static inline unsigned int read_feat_sve_id_field(void)
 {
-	return (((read_id_aa64pfr0_el1() >> ID_AA64PFR0_SVE_SHIFT) &
-		ID_AA64PFR0_SVE_MASK) == ID_AA64PFR0_SVE_SUPPORTED);
+	return ISOLATE_FIELD(read_id_aa64pfr0_el1(), ID_AA64PFR0_SVE);
+}
+
+static inline bool is_feat_sve_supported(void)
+{
+	if (ENABLE_SVE_FOR_NS == FEAT_STATE_DISABLED) {
+		return false;
+	}
+
+	if (ENABLE_SVE_FOR_NS == FEAT_STATE_ALWAYS) {
+		return true;
+	}
+
+	return read_feat_sve_id_field() >= ID_AA64PFR0_SVE_SUPPORTED;
 }
 
 /*******************************************************************************
diff --git a/include/lib/extensions/sve.h b/include/lib/extensions/sve.h
index 4b66cdb09..1faed2d23 100644
--- a/include/lib/extensions/sve.h
+++ b/include/lib/extensions/sve.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2021, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2023, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,7 +9,16 @@
 
 #include <context.h>
 
+#if (ENABLE_SME_FOR_NS || ENABLE_SVE_FOR_NS)
 void sve_enable(cpu_context_t *context);
 void sve_disable(cpu_context_t *context);
+#else
+static inline void sve_enable(cpu_context_t *context)
+{
+}
+static inline void sve_disable(cpu_context_t *context)
+{
+}
+#endif /* ( ENABLE_SME_FOR_NS | ENABLE_SVE_FOR_NS ) */
 
 #endif /* SVE_H */
diff --git a/lib/el3_runtime/aarch64/context_mgmt.c b/lib/el3_runtime/aarch64/context_mgmt.c
index 7fbbd8171..42166eb99 100644
--- a/lib/el3_runtime/aarch64/context_mgmt.c
+++ b/lib/el3_runtime/aarch64/context_mgmt.c
@@ -492,11 +492,10 @@ static void manage_extensions_nonsecure(bool el2_unused, cpu_context_t *ctx)
 	/* Enable SME, SVE, and FPU/SIMD for non-secure world. */
 	if (is_feat_sme_supported()) {
 		sme_enable(ctx);
+	} else if (is_feat_sve_supported()) {
+		/* Enable SVE and FPU/SIMD for non-secure world. */
+		sve_enable(ctx);
 	}
-#if ENABLE_SVE_FOR_NS
-	/* Enable SVE and FPU/SIMD for non-secure world. */
-	sve_enable(ctx);
-#endif
 
 	if (is_feat_mpam_supported()) {
 		mpam_enable(el2_unused);
@@ -526,35 +525,38 @@ static void manage_extensions_nonsecure(bool el2_unused, cpu_context_t *ctx)
 static void manage_extensions_secure(cpu_context_t *ctx)
 {
 #if IMAGE_BL31
- #if ENABLE_SME_FOR_NS
-  #if ENABLE_SME_FOR_SWD
-	/*
-	 * Enable SME, SVE, FPU/SIMD in secure context, secure manager must
-	 * ensure SME, SVE, and FPU/SIMD context properly managed.
-	 */
-	sme_enable(ctx);
-  #else /* ENABLE_SME_FOR_SWD */
-	/*
-	 * Disable SME, SVE, FPU/SIMD in secure context so non-secure world can
-	 * safely use the associated registers.
-	 */
-	sme_disable(ctx);
-  #endif /* ENABLE_SME_FOR_SWD */
- #elif ENABLE_SVE_FOR_NS
-  #if ENABLE_SVE_FOR_SWD
-	/*
-	 * Enable SVE and FPU in secure context, secure manager must ensure that
-	 * the SVE and FPU register contexts are properly managed.
-	 */
-	sve_enable(ctx);
- #else /* ENABLE_SVE_FOR_SWD */
-	/*
-	 * Disable SVE and FPU in secure context so non-secure world can safely
-	 * use them.
-	 */
-	sve_disable(ctx);
-  #endif /* ENABLE_SVE_FOR_SWD */
- #endif /* ENABLE_SVE_FOR_NS */
+
+	if (is_feat_sme_supported()) {
+		if (ENABLE_SME_FOR_SWD) {
+		/*
+		 * Enable SME, SVE, FPU/SIMD in secure context, secure manager
+		 * must ensure SME, SVE, and FPU/SIMD context properly managed.
+		 */
+			sme_enable(ctx);
+		} else {
+		/*
+		 * Disable SME, SVE, FPU/SIMD in secure context so non-secure
+		 * world can safely use the associated registers.
+		 */
+			sme_disable(ctx);
+		}
+	} else if (is_feat_sve_supported()) {
+		if (ENABLE_SVE_FOR_SWD) {
+		/*
+		 * Enable SVE and FPU in secure context, secure manager must
+		 * ensure that the SVE and FPU register contexts are properly
+		 * managed.
+		 */
+			sve_enable(ctx);
+		} else {
+		/*
+		 * Disable SVE and FPU in secure context so non-secure world
+		 * can safely use them.
+		 */
+			sve_disable(ctx);
+		}
+	}
+
 #endif /* IMAGE_BL31 */
 }
 
diff --git a/lib/extensions/sme/sme.c b/lib/extensions/sme/sme.c
index 1846e003a..29034fdc4 100644
--- a/lib/extensions/sme/sme.c
+++ b/lib/extensions/sme/sme.c
@@ -20,13 +20,6 @@ void sme_enable(cpu_context_t *context)
 	u_register_t cptr_el3;
 	el3_state_t *state;
 
-	/* Make sure SME is implemented in hardware before continuing. */
-	if (!is_feat_sme_supported()) {
-		/* Perhaps the hardware supports SVE only */
-		sve_enable(context);
-		return;
-	}
-
 	/* Get the context state. */
 	state = get_el3state_ctx(context);
 
@@ -70,13 +63,6 @@ void sme_disable(cpu_context_t *context)
 	u_register_t reg;
 	el3_state_t *state;
 
-	/* Make sure SME is implemented in hardware before continuing. */
-	if (!is_feat_sme_supported()) {
-		/* Perhaps the hardware supports SVE only */
-		sve_disable(context);
-		return;
-	}
-
 	/* Get the context state. */
 	state = get_el3state_ctx(context);
 
diff --git a/lib/extensions/sve/sve.c b/lib/extensions/sve/sve.c
index f7dcc767a..f551ca7e6 100644
--- a/lib/extensions/sve/sve.c
+++ b/lib/extensions/sve/sve.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2022, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2023, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -22,22 +22,10 @@ CASSERT((SVE_VECTOR_LEN % 128) == 0, assert_sve_vl_granule);
  */
 #define CONVERT_SVE_LENGTH(x)	(((x / 128) - 1))
 
-static bool sve_supported(void)
-{
-	uint64_t features;
-
-	features = read_id_aa64pfr0_el1() >> ID_AA64PFR0_SVE_SHIFT;
-	return (features & ID_AA64PFR0_SVE_MASK) == 1U;
-}
-
 void sve_enable(cpu_context_t *context)
 {
 	u_register_t cptr_el3;
 
-	if (!sve_supported()) {
-		return;
-	}
-
 	cptr_el3 = read_ctx_reg(get_el3state_ctx(context), CTX_CPTR_EL3);
 
 	/* Enable access to SVE functionality for all ELs. */
@@ -54,11 +42,6 @@ void sve_disable(cpu_context_t *context)
 	u_register_t reg;
 	el3_state_t *state;
 
-	/* Make sure SME is implemented in hardware before continuing. */
-	if (!sve_supported()) {
-		return;
-	}
-
 	/* Get the context state. */
 	state = get_el3state_ctx(context);
 
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index ef917f65b..63617b2ae 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -373,7 +373,7 @@ ENABLE_AMU_FCONF		:= 0
 AMU_RESTRICT_COUNTERS		:= 0
 
 # Enable SVE for non-secure world by default
-ENABLE_SVE_FOR_NS		:= 1
+ENABLE_SVE_FOR_NS		:= 2
 # SVE is only supported on AArch64 so disable it on AArch32.
 ifeq (${ARCH},aarch32)
 	override ENABLE_SVE_FOR_NS	:= 0
diff --git a/services/std_svc/rmmd/rmmd_main.c b/services/std_svc/rmmd/rmmd_main.c
index e12eae79f..24f6c4127 100644
--- a/services/std_svc/rmmd/rmmd_main.c
+++ b/services/std_svc/rmmd/rmmd_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2022, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2021-2023, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -117,19 +117,14 @@ static void rmm_el2_context_init(el2_sysregs_t *regs)
  ******************************************************************************/
 static void manage_extensions_realm(cpu_context_t *ctx)
 {
-#if ENABLE_SVE_FOR_NS
+	if (is_feat_sve_supported()) {
 	/*
 	 * Enable SVE and FPU in realm context when it is enabled for NS.
 	 * Realm manager must ensure that the SVE and FPU register
 	 * contexts are properly managed.
 	 */
-	sve_enable(ctx);
-#else
-	/*
-	 * Disable SVE and FPU in realm context when it is disabled for NS.
-	 */
-	sve_disable(ctx);
-#endif /* ENABLE_SVE_FOR_NS */
+		sve_enable(ctx);
+	}
 }
 
 /*******************************************************************************
diff --git a/services/std_svc/spm/spm_mm/spm_mm.mk b/services/std_svc/spm/spm_mm/spm_mm.mk
index b1f045ee6..513e8ef96 100644
--- a/services/std_svc/spm/spm_mm/spm_mm.mk
+++ b/services/std_svc/spm/spm_mm/spm_mm.mk
@@ -10,7 +10,7 @@ endif
 ifneq (${ARCH},aarch64)
         $(error "Error: SPM_MM is only supported on aarch64.")
 endif
-ifeq (${ENABLE_SVE_FOR_NS},1)
+ifneq (${ENABLE_SVE_FOR_NS},0)
         $(error "Error: SPM_MM is not compatible with ENABLE_SVE_FOR_NS")
 endif
 ifneq (${ENABLE_SME_FOR_NS},0)