Enable v8.6 WFE trap delays
This patch enables the v8.6 extension to add a delay before WFE traps
are taken. A weak hook plat_arm_set_twedel_scr_el3 has been added in
plat/common/aarch64/plat_common.c that disables this feature by default
but platform-specific code can override it when needed.
The only hook provided sets the TWED fields in SCR_EL3, there are similar
fields in HCR_EL2, SCTLR_EL2, and SCTLR_EL1 to control WFE trap delays in
lower ELs but these should be configured by code running at EL2 and/or EL1
depending on the platform configuration and is outside the scope of TF-A.
Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: I0a9bb814205efeab693a3d0a0623e62144abba2d
diff --git a/docs/getting_started/porting-guide.rst b/docs/getting_started/porting-guide.rst
index 2d17f12..2ad7256 100644
--- a/docs/getting_started/porting-guide.rst
+++ b/docs/getting_started/porting-guide.rst
@@ -1890,6 +1890,21 @@
of the system counter, which is retrieved from the first entry in the frequency
modes table.
+Function : plat_arm_set_twedel_scr_el3() [optional]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ Argument : void
+ Return : uint32_t
+
+This function is used in v8.6+ systems to set the WFE trap delay value in
+SCR_EL3. If this function returns TWED_DISABLED or is left unimplemented, this
+feature is not enabled. The only hook provided is to set the TWED fields in
+SCR_EL3, there are similar fields in HCR_EL2, SCTLR_EL2, and SCTLR_EL1 to adjust
+the WFE trap delays in lower ELs and these fields should be set by the
+appropriate EL2 or EL1 code depending on the platform configuration.
+
#define : PLAT_PERCPU_BAKERY_LOCK_SIZE [optional]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~