refactor(cpufeat): align FEAT_SB to new feature handling

FEAT_SB introduces a new speculation barrier instruction, that is more
lightweight than a "dsb; isb" combination. We use that in a hot path,
so cannot afford and don't want a runtime detection mechanism.
Nevertheless align the implementation of the feature detection part
with the other features, but renaming the detection function, and
updating the FEAT_DETECTION code. Also update the documentation.

Change-Id: I2b86dfd1ad259c3bb99ab5186e2911ace454b54c
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

diff --git a/Makefile b/Makefile
index 8e789def0c3388afacc03dff03e421152dd1805c..90d8bbf180c024a81d59199c4ea8ca4071cf7eeb 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1090,6 +1090,7 @@ $(eval $(call assert_booleans,\
         ENABLE_AMU_FCONF \
         AMU_RESTRICT_COUNTERS \
         ENABLE_ASSERTIONS \
+        ENABLE_FEAT_SB \
         ENABLE_PIE \
         ENABLE_PMF \
         ENABLE_PSCI_STAT \
@@ -1174,7 +1175,6 @@ $(eval $(call assert_numerics,\
         ENABLE_FEAT_PAN \
         ENABLE_FEAT_RNG \
         ENABLE_FEAT_RNG_TRAP \
-        ENABLE_FEAT_SB \
         ENABLE_FEAT_SEL2 \
         ENABLE_FEAT_TCR2 \
         ENABLE_FEAT_VHE \

diff --git a/common/feat_detect.c b/common/feat_detect.c
index 7a6c9193e9ed539913516faf814c3a05aef34353..4b5dcd462d5575f7e391364c11080ba6938ea8f8 100644 (file)
--- a/common/feat_detect.c
+++ b/common/feat_detect.c
@@ -60,16 +60,6 @@ check_feature(int state, unsigned long field, const char *feat_name,
        }
 }
 
-/******************************************
- * Feature : FEAT_SB (Speculation Barrier)
- *****************************************/
-static void read_feat_sb(void)
-{
-#if (ENABLE_FEAT_SB == FEAT_STATE_ALWAYS)
-       feat_detect_panic(is_armv8_0_feat_sb_present(), "SB");
-#endif
-}
-
 /******************************************************
  * Feature : FEAT_CSV2_2 (Cache Speculation Variant 2)
  *****************************************************/
@@ -256,7 +246,7 @@ void detect_arch_features(void)
        tainted = false;
 
        /* v8.0 features */
-       read_feat_sb();
+       check_feature(ENABLE_FEAT_SB, read_feat_sb_id_field(), "SB", 1, 1);
        read_feat_csv2_2();
 
        /* v8.1 features */

diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 94c12defeebd19a9a80c3d22e8be2eb595a8b44f..0540b6d2fc560988ad82b1f334ed6ba819a1d9d8 100644 (file)
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -327,12 +327,11 @@ Common build options
    Default value is ``0``. ``FEAT_RNG_TRAP`` is an optional feature from
    Armv8.5 onwards.
 
--  ``ENABLE_FEAT_SB``: Numeric value to enable the ``FEAT_SB`` (Speculation
-   Barrier) extension allowing access to ``sb`` instruction. ``FEAT_SB`` is an
-   optional feature and defaults to ``0`` for pre-Armv8.5 CPUs but are mandatory
-   for Armv8.5 or later CPUs. This flag can take values 0 to 2, to align with
-   ``FEATURE_DETECTION`` mechanism. It is enabled from v8.5 and upwards and if
-   needed could be overidden from platforms explicitly. Default value is ``0``.
+-  ``ENABLE_FEAT_SB``: Boolean option to let the TF-A code use the ``FEAT_SB``
+   (Speculation Barrier) instruction ``FEAT_SB`` is an optional feature and
+   defaults to ``0`` for pre-Armv8.5 CPUs, but is mandatory for Armv8.5 or
+   later CPUs. It is enabled from v8.5 and upwards and if needed can be
+   overidden from platforms explicitly.
 
 -  ``ENABLE_FEAT_SEL2``: Numeric value to enable the ``FEAT_SEL2`` (Secure EL2)
    extension. ``FEAT_SEL2`` is a mandatory feature available on Arm v8.4.

diff --git a/include/arch/aarch64/arch_features.h b/include/arch/aarch64/arch_features.h
index ad938aea3062ad3a279e191f2363b5aa6b180e48..1af7758760f9efe81cb5633d93b0c3a771733408 100644 (file)
--- a/include/arch/aarch64/arch_features.h
+++ b/include/arch/aarch64/arch_features.h
@@ -256,10 +256,9 @@ static inline unsigned int get_armv9_2_feat_rme_support(void)
 /*********************************************************************************
  * Function to identify the presence of FEAT_SB (Speculation Barrier Instruction)
  ********************************************************************************/
-static inline bool is_armv8_0_feat_sb_present(void)
+static inline unsigned int read_feat_sb_id_field(void)
 {
-       return (((read_id_aa64isar1_el1() >> ID_AA64ISAR1_SB_SHIFT) &
-               ID_AA64ISAR1_SB_MASK) == ID_AA64ISAR1_SB_SUPPORTED);
+       return ISOLATE_FIELD(read_id_aa64isar1_el1(), ID_AA64ISAR1_SB);
 }
 
 /*********************************************************************************