feat: pass SMCCCv1.3 SVE hint bit to dispatchers

SMCCCv1.3 introduces the SVE hint bit added to the SMC FID (bit 16)
denoting that the world issuing an SMC doesn't expect the callee to
preserve the SVE state (FFR, predicates, Zn vector bits greater than
127). Update the generic SMC handler to copy the SVE hint bit state
to SMC flags and mask out the bit by default for the services called
by the standard dispatcher. It is permitted by the SMCCC standard to
ignore the bit as long as the SVE state is preserved. In any case a
callee must preserve the NEON state (FPCR/FPSR, Vn 128b vectors)
whichever the SVE hint bit state.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I2b163ed83dc311b8f81f96b23c942829ae9fa1b5
diff --git a/bl31/aarch64/runtime_exceptions.S b/bl31/aarch64/runtime_exceptions.S
index bf5bd8d..0283553 100644
--- a/bl31/aarch64/runtime_exceptions.S
+++ b/bl31/aarch64/runtime_exceptions.S
@@ -512,7 +512,7 @@
 	 * Shift copied SCR_EL3.NSE bit by 5 to create space for
-	 * SCR_EL3.NS bit. Bit 5 of the flag correspondes to
+	 * SCR_EL3.NS bit. Bit 5 of the flag corresponds to
 	 * the SCR_EL3.NSE bit.
 	lsl	x7, x7, #5
@@ -521,6 +521,16 @@
 	/* Copy SCR_EL3.NS bit to the flag to indicate caller's security */
 	bfi	x7, x18, #0, #1
+	/*
+	 * Per SMCCCv1.3 a caller can set the SVE hint bit in the SMC FID
+	 * passed through x0. Copy the SVE hint bit to flags and mask the
+	 * bit in smc_fid passed to the standard service dispatcher.
+	 * A service/dispatcher can retrieve the SVE hint bit state from
+	 * flags using the appropriate helper.
+	 */
 	mov	sp, x12
 	/* Get the unique owning entity number */
diff --git a/docs/design/firmware-design.rst b/docs/design/firmware-design.rst
index 71fdfcb..84bba18 100644
--- a/docs/design/firmware-design.rst
+++ b/docs/design/firmware-design.rst
@@ -990,9 +990,10 @@
 directly, the others are saved into memory for retrieval (if needed) by the
 handler. The handler is also provided with an opaque ``handle`` for use with the
 supporting library for parameter retrieval, setting return values and context
-manipulation; and with ``flags`` indicating the security state of the caller. The
-framework finally sets up the execution stack for the handler, and invokes the
-services ``handle()`` function.
+manipulation. The ``flags`` parameter indicates the security state of the caller
+and the state of the SVE hint bit per the SMCCCv1.3. The framework finally sets
+up the execution stack for the handler, and invokes the services ``handle()``
 On return from the handler the result registers are populated in X0-X7 as needed
 before restoring the stack and CPU state and returning from the original SMC.
diff --git a/include/lib/smccc.h b/include/lib/smccc.h
index 9940ea9..cce91af 100644
--- a/include/lib/smccc.h
+++ b/include/lib/smccc.h
@@ -37,6 +37,10 @@
 #define FUNCID_OEN_MASK			U(0x3f)
 #define FUNCID_OEN_WIDTH		U(6)
+#define FUNCID_SVE_HINT_SHIFT          U(16)
+#define FUNCID_SVE_HINT_MASK           U(1)
+#define FUNCID_SVE_HINT_WIDTH          U(1)
 #define FUNCID_NUM_SHIFT		U(0)
 #define FUNCID_NUM_MASK			U(0xffff)
 #define FUNCID_NUM_WIDTH		U(16)
@@ -122,6 +126,12 @@
  *   0        0      SMC_FROM_SECURE
  *   0        1      SMC_FROM_NON_SECURE
  *   1        1      SMC_FROM_REALM
+ *
+ * Bit 16 of flags records the caller's SMC
+ * SVE hint bit according to SMCCCv1.3.
+ * It can be consumed by dispatchers using
+ * is_sve_hint_set macro.
+ *
 #define SMC_FROM_SECURE		(U(0) << 0)
@@ -148,6 +158,9 @@
 #define is_caller_secure(_f)		(!is_caller_non_secure(_f))
 #endif /* ENABLE_RME */
+#define is_sve_hint_set(_f)		(((_f) & (FUNCID_SVE_HINT_MASK \
+						<< FUNCID_SVE_HINT_SHIFT)) != U(0))
 /* The macro below is used to identify a Standard Service SMC call */
 #define is_std_svc_call(_fid)		(GET_SMC_OEN(_fid) == OEN_STD_START)