bl31: Split into two separate memory regions
Some platforms are extremely memory constrained and must split BL31
between multiple non-contiguous areas in SRAM. Allow the NOBITS
sections (.bss, stacks, page tables, and coherent memory) to be placed
in a separate region of RAM from the loaded firmware image.
Because the NOBITS region may be at a lower address than the rest of
BL31, __RW_{START,END}__ and __BL31_{START,END}__ cannot include this
region, or el3_entrypoint_common would attempt to invalidate the dcache
for the entire address space. New symbols __NOBITS_{START,END}__ are
added when SEPARATE_NOBITS_REGION is enabled, and the dcached for the
NOBITS region is invalidated separately.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: Idedfec5e4dbee77e94f2fdd356e6ae6f4dc79d37
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 37c28a5..d7bb044 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -491,6 +491,13 @@
pages" section in :ref:`Firmware Design`. This flag is disabled by default and
affects all BL images.
+- ``SEPARATE_NOBITS_REGION``: Setting this option to ``1`` allows the NOBITS
+ sections of BL31 (.bss, stacks, page tables, and coherent memory) to be
+ allocated in RAM discontiguous from the loaded firmware image. When set, the
+ platform is expected to provide definitons for ``BL31_NOBITS_BASE`` and
+ ``BL31_NOBITS_LIMIT``. When the option is ``0`` (the default), NOBITS
+ sections are placed in RAM immediately following the loaded firmware image.
+
- ``SPD``: Choose a Secure Payload Dispatcher component to be built into TF-A.
This build option is only valid if ``ARCH=aarch64``. The value should be
the path to the directory containing the SPD source, relative to