refactor(cpufeat): enable FEAT_DIT for FEAT_STATE_CHECKED

At the moment we only support FEAT_DIT to be either unconditionally
compiled in, or to be not supported at all.

Add support for runtime detection (ENABLE_DIT=2), by splitting
is_armv8_4_dit_present() 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).

We use ENABLE_DIT in two occassions in assembly code, where we just set
the DIT bit in the DIT system register.
Protect those two cases by reading the CPU ID register when ENABLE_DIT
is set to 2.

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: I506d352f18e23c60db8cdf08edb449f60adbe098
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

3 files changed, 40 insertions, 13 deletions

diff --git a/include/arch/aarch32/arch_features.h b/include/arch/aarch32/arch_features.h
index 7c25b99ac..62a512b3e 100644
--- a/include/arch/aarch32/arch_features.h
+++ b/include/arch/aarch32/arch_features.h
@@ -92,6 +92,24 @@ static inline bool is_feat_sys_reg_trace_supported(void)
 	return read_feat_coptrc_id_field() != 0U;
 }
 
+static inline unsigned int read_feat_dit_id_field(void)
+{
+	return ISOLATE_FIELD(read_id_pfr0(), ID_PFR0_DIT);
+}
+
+static inline bool is_feat_dit_supported(void)
+{
+	if (ENABLE_FEAT_DIT == FEAT_STATE_DISABLED) {
+		return false;
+	}
+
+	if (ENABLE_FEAT_DIT == FEAT_STATE_ALWAYS) {
+		return true;
+	}
+
+	return read_feat_dit_id_field() != 0U;
+}
+
 static inline bool is_feat_spe_supported(void)
 {
 	/* FEAT_SPE is AArch64 only */
diff --git a/include/arch/aarch64/arch_features.h b/include/arch/aarch64/arch_features.h
index 16f4fb996..40ab82fb0 100644
--- a/include/arch/aarch64/arch_features.h
+++ b/include/arch/aarch64/arch_features.h
@@ -89,12 +89,6 @@ static inline bool is_armv8_3_pauth_present(void)
 		is_feat_pacqarma3_present());
 }
 
-static inline bool is_armv8_4_dit_present(void)
-{
-	return ((read_id_aa64pfr0_el1() >> ID_AA64PFR0_DIT_SHIFT) &
-		ID_AA64PFR0_DIT_MASK) == 1U;
-}
-
 static inline bool is_armv8_4_ttst_present(void)
 {
 	return ((read_id_aa64mmfr2_el1() >> ID_AA64MMFR2_EL1_ST_SHIFT) &
@@ -515,13 +509,22 @@ static inline bool is_armv8_2_feat_ras_present(void)
 		ID_AA64PFR0_RAS_MASK) != ID_AA64PFR0_RAS_NOT_SUPPORTED);
 }
 
-/**************************************************************************
- * Function to identify the presence of FEAT_DIT (Data Independent Timing)
- *************************************************************************/
-static inline bool is_armv8_4_feat_dit_present(void)
+static unsigned int read_feat_dit_id_field(void)
+{
+	return ISOLATE_FIELD(read_id_aa64pfr0_el1(), ID_AA64PFR0_DIT);
+}
+
+static inline bool is_feat_dit_supported(void)
 {
-	return (((read_id_aa64pfr0_el1() >> ID_AA64PFR0_DIT_SHIFT) &
-		ID_AA64PFR0_DIT_MASK) == ID_AA64PFR0_DIT_SUPPORTED);
+	if (ENABLE_FEAT_DIT == FEAT_STATE_DISABLED) {
+		return false;
+	}
+
+	if (ENABLE_FEAT_DIT == FEAT_STATE_ALWAYS) {
+		return true;
+	}
+
+	return read_feat_dit_id_field() != 0U;
 }
 
 static inline unsigned int read_feat_tracever_id_field(void)
diff --git a/include/arch/aarch64/el3_common_macros.S b/include/arch/aarch64/el3_common_macros.S
index 45a86c10e..2dee07d2a 100644
--- a/include/arch/aarch64/el3_common_macros.S
+++ b/include/arch/aarch64/el3_common_macros.S
@@ -243,14 +243,20 @@
 	 * register value for DIT.
 	 */
 #if ENABLE_FEAT_DIT
-#if ENABLE_ASSERTIONS
+#if ENABLE_ASSERTIONS || ENABLE_FEAT_DIT > 1
 	mrs	x0, id_aa64pfr0_el1
 	ubfx	x0, x0, #ID_AA64PFR0_DIT_SHIFT, #ID_AA64PFR0_DIT_LENGTH
+#if ENABLE_FEAT_DIT > 1
+	cbz	x0, 1f
+#else
 	cmp	x0, #ID_AA64PFR0_DIT_SUPPORTED
 	ASM_ASSERT(eq)
+#endif
+
 #endif /* ENABLE_ASSERTIONS */
 	mov	x0, #DIT_BIT
 	msr	DIT, x0
+1:
 #endif
 	.endm