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libpayload: mips: Do not set C0_EBase_WG 

The WG (write gate) bit in C0_EBase allows the upper two bits of
the exception base address to be set to something other than 2'b10,
thus allowing it to be relocated out of the traditional KSEG{0,1}
range.  Since we're not using the segmentation features introduced
by EVA to relocate the unmapped segments, the exception vectors
should remain in KSEG0.  Don't set the WG bit so that the upper
two bits of the exception base (2'b00, because of the identity
mapping) are ignored and we execute the exception vectors out of
KSEG0.

BUG=chrome-os-partner:36258
BRANCH=none
TEST=Build and boot on Pistachio.

Change-Id: Ie8b4eb6e41a328e7055736c9e3f6ff5ec83b9e13
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: d5b002f5ae71c7729e467d4fe3fd8db187e15dea
Original-Change-Id: Id8b930db1e7a68f52dd61be4dfa9edaee2bebf7d
Original-Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/246697
Original-Reviewed-by: Ionela Voinescu <ionela.voinescu@imgtec.com>
Original-Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Tested-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Commit-Queue: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: http://review.coreboot.org/9822
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
This commit is contained in:
Andrew Bresticker 2015-02-05 13:51:50 -08:00 committed by Patrick Georgi
parent ca0e89b61e
commit 44c5105890
1 changed files with 0 additions and 4 deletions
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4
payloads/libpayload/arch/mips/exception_asm.S
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@ -20,7 +20,6 @@
#define STATUS_REGISTER $12,0
#define BOOT_EXC_VECTOR_MASK (1 << 22)
#define EBASE_REGISTER $15,1
#define WRITE_GATE_MASK (1 << 11)
#define EXCEPTION_BASE_MASK (0xFFFFF000)
/* Don't reorder instructions */
@ -192,9 +191,6 @@ exception_init_asm:
and $t0, $t0, $t2
/* Filling base address */
or $t0, $t0, $t1
/* Setting WG bit */
li $t2, WRITE_GATE_MASK
or $t0, $t0, $t2
mtc0 $t0, EBASE_REGISTER
/* Clear boot exception vector bit for EBASE value to take effect */