Set armv7 up for cpu_info to work as on x86 (so threads can work)

On x86, cpu_info lives at the top of stack. Make the arm do that as
well, as the threading model needs that and so will multicore support.

As part of this change, make the stack size a power of 2.
Also make it much smaller -- 2048 bytes is PLENTY for ram stage.

Note that the small stack size is counterintuitive for rom stage.  How
can this work in rom stage, which needs a HUGE stack for lzma? The
main use of STACK_SIZE has always been in ram stage; since 2002 or so
it was to size per-core stacks (see, e.g.,

src/arch/x86/lib/c_start.S:.space CONFIG_MAX_CPUS*CONFIG_STACK_SIZE

and, more recently, thread stacks. So, we define the STACK_TOP for rom
and ram stage, but the STACK_SIZE has no real effect on the ROM stage
(no hardware red zones on the stack) and hence we're ok with actually
defining the "wrong" stack size. In fact, the coreboot_ram ldscript
for armv7 sizes the stack by subtracting CONFIG_STACK_BOTTOM from
CONFIG_STACK_TOP, so we replicate that arithmetic in bootblock.inc

Observed stack usage in ramstage:
BS: BS_PAYLOAD_LOAD times (us): entry 1 run 153887 exit 1
Jumping to boot code at 23104044
CPU0: stack: 02072800 - 02073000, lowest used address 020728d4, stack used: 1836 bytes
entry    = 23104044

Which means we do need 2K, not 1K.

Change-Id: I1a21db87081597efe463095bfd33c89eba1d569f
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/66135
Reviewed-by: Ronald G. Minnich <rminnich@chromium.org>
Tested-by: Ronald G. Minnich <rminnich@chromium.org>
Commit-Queue: Ronald G. Minnich <rminnich@chromium.org>
(cherry picked from commit f011097e9f2bfb2f4c1109d465be89a79a65ba3e)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6501
Tested-by: build bot (Jenkins)
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

1 files changed, 20 insertions, 2 deletions

diff --git a/src/cpu/samsung/exynos5420/Kconfig b/src/cpu/samsung/exynos5420/Kconfig
index d3eafcba75..66679a000b 100644
--- a/src/cpu/samsung/exynos5420/Kconfig
+++ b/src/cpu/samsung/exynos5420/Kconfig
@@ -69,7 +69,17 @@ config ROMSTAGE_SIZE
 # at the top of IRAM for now.
 #
 # Stack grows downward, push operation stores register contents in
-# consecutive memory locations ending just below SP
+# consecutive memory locations ending just below SP.
+# The setup in the exynos 5420 is a new one for coreboot. We have got
+# the bootblock, romstage, and ramstage sharing the same stack space.
+# The SRAM is always there and having a known-good stack memory
+# makes for a more reliable setup.
+# Thus, in this case:
+# STACK_TOP: highest stack address in SRAM
+# STACK_BOTTOM: lowest stack address in SRAM
+# STACK_SIZE: as in standard coreboot usage, size of thread stacks in ramstage
+# ROMSTAGE_STACK_SIZE: size of the single stack in romstage
+
 config STACK_TOP
 	hex
 	default 0x02073000
@@ -78,10 +88,18 @@ config STACK_BOTTOM
 	hex
 	default 0x0206f000
 
-config STACK_SIZE
+# The romstage stack must be large enough to contain the lzma buffer
+config ROMSTAGE_STACK_SIZE
 	hex
 	default 0x4000
 
+# STACK_SIZE is for the ramstage core and thread stacks.
+# It must be a power of 2, to make the cpu_info computation work,
+# and cpu_info needs to work to make SMP startup and threads work.
+config STACK_SIZE
+	hex
+	default 0x0800
+
 # TODO We may probably move this to board-specific implementation files instead
 # of KConfig values.
 config CBFS_CACHE_ADDRESS