[PATCH 02/10] OMAP3 SRAM: add ARM barriers to omap3_sram_configure_core_dpll

Paul Walmsley
2009-05-13T00:08:25Z

Add more barriers in the SRAM CORE DPLL M2 divider change code.

- Add a DSB SY after the function's entry point to flush all cached
and buffered writes and wait for the interconnect to claim that they
have completed[1]. The idea here is to force all delayed write
traffic going to the SDRAM to at least post to the L3 interconnect
before continuing. If these writes are allowed to occur after the
SDRC is idled, the writes will not be acknowledged and the ARM will
stall.

Note that in this case, it does not matter if the writes actually
complete to the SDRAM - it is only necessary for the writes to leave
the ARM itself. If the writes are posted by the interconnect when
the SDRC goes into idle, the writes will be delayed until the SDRC
returns from idle[2]. If the SDRC is in the middle of a write when
it is requested to enter idle, the SDRC will not acknowledge the
idle request until the writes complete to the SDRAM.[3]

The old-style DMB in sdram_in_selfrefresh is now superfluous, so,
remove it.

- Add an ISB before the function's exit point to prevent the ARM from
speculatively executing into SDRAM before the SDRAM is enabled[4].

...

1. ARMv7 ARM (DDI 0406A) A3-47, A3-48.

2. Private communication with Richard Woodruff <r-woodruff2@ti.com>.

3. Private communication with Richard Woodruff <r-woodruff2@ti.com>.

4. ARMv7 ARM (DDI 0406A) A3-48.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>
---
arch/arm/mach-omap2/sram34xx.S | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mach-omap2/sram34xx.S b/arch/arm/mach-omap2/sram34xx.S
index 2c71461..f4a356d 100644
--- a/arch/arm/mach-omap2/sram34xx.S
+++ b/arch/arm/mach-omap2/sram34xx.S
@@ -43,6 +43,7 @@
*/
ENTRY(omap3_sram_configure_core_dpll)
stmfd sp!, {r1-r12, lr} @ store regs to stack
+ dsb @ flush buffered writes to interconnect
cmp r3, #0x2
blne configure_sdrc
cmp r3, #0x2
@@ -58,6 +59,7 @@ ENTRY(omap3_sram_configure_core_dpll)
blne wait_dll_lock
cmp r3, #0x1
blne configure_sdrc
+ isb @ prevent speculative exec past here
mov r0, #0 @ return value
ldmfd sp!, {r1-r12, pc} @ restore regs and return
unlock_dll:
@@ -73,8 +75,6 @@ lock_dll:
str r5, [r4]
bx lr
sdram_in_selfrefresh:
- mov r5, #0x0 @ Move 0 to R5
- mcr p15, 0, r5, c7, c10, 5 @ memory barrier
ldr r4, omap3_sdrc_power @ read the SDRC_POWER register
ldr r5, [r4] @ read the contents of SDRC_POWER
orr r5, r5, #0x40 @ enable self refresh on idle req