DynamIQ: Enable MMU without using stack

Having an active stack while enabling MMU has shown coherency problems.
This patch builds on top of translation library changes that introduces
MMU-enabling without using stacks.

Previously, with HW_ASSISTED_COHERENCY, data caches were disabled while
enabling MMU only because of active stack. Now that we can enable MMU
without using stack, we can enable both MMU and data caches at the same
time.

NOTE: Since this feature depends on using translation table library v2,
disallow using translation table library v1 with HW_ASSISTED_COHERENCY.

Fixes ARM-software/tf-issues#566

Change-Id: Ie55aba0c23ee9c5109eb3454cb8fa45d74f8bbb2
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index a737cf4e6..5462cc1ec 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -1997,6 +1997,25 @@ state. This function must return a pointer to the ``entry_point_info`` structure
 (that was copied during ``bl31_early_platform_setup()``) if the image exists. It
 should return NULL otherwise.
 
+Function : bl31_plat_enable_mmu [optional]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    Argument : uint32_t
+    Return   : void
+
+This function enables the MMU. The boot code calls this function with MMU and
+caches disabled. This function should program necessary registers to enable
+translation, and upon return, the MMU on the calling PE must be enabled.
+
+The function must honor flags passed in the first argument. These flags are
+defined by the translation library, and can be found in the file
+``include/lib/xlat_tables/xlat_mmu_helpers.h``.
+
+On DynamIQ systems, this function must not use stack while enabling MMU, which
+is how the function in xlat table library version 2 is implementated.
+
 Function : plat\_get\_syscnt\_freq2() [mandatory]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~