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| author | Paul Walmsley <paul@pwsan.com> | 2009-06-20 05:08:26 +0400 |
|---|---|---|
| committer | paul <paul@twilight.(none)> | 2009-06-20 05:09:31 +0400 |
| commit | c9812d042a21eb492a36cfabf9f41107f5ecee3d (patch) | |
| tree | f9443de1d4534b0b56bd1b0ff56bfc6d78eb698d /arch/arm/mach-omap2/sram34xx.S | |
| parent | 2f135eaf182761bb9a5cbd5138a447b0ad2a1fef (diff) | |
| download | linux-c9812d042a21eb492a36cfabf9f41107f5ecee3d.tar.xz | |
OMAP3 clock: add a short delay when lowering CORE clk rate
When changing the SDRAM clock from 166MHz to 83MHz via the CORE DPLL M2
divider, add a short delay before returning to SDRAM to allow the SDRC
time to stabilize. Without this delay, the system is prone to random
panics upon re-entering SDRAM.
This time delay varies based on MPU frequency. At 500MHz MPU frequency at
room temperature, 64 loops seems to work okay; so add another 32 loops for
environmental and process variation.
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Diffstat (limited to 'arch/arm/mach-omap2/sram34xx.S')
| -rw-r--r-- | arch/arm/mach-omap2/sram34xx.S | 20 |
1 files changed, 9 insertions, 11 deletions
diff --git a/arch/arm/mach-omap2/sram34xx.S b/arch/arm/mach-omap2/sram34xx.S index 84781a6cd263..8d4a88c30718 100644 --- a/arch/arm/mach-omap2/sram34xx.S +++ b/arch/arm/mach-omap2/sram34xx.S @@ -42,10 +42,14 @@ * r0 = sdrc_rfr_ctrl r1 = sdrc_actim_ctrla r2 = sdrc_actim_ctrlb r3 = M2 * r4 = Unlock SDRC DLL? (1 = yes, 0 = no) -- only unlock DLL for * SDRC rates < 83MHz + * r5 = number of MPU cycles to wait for SDRC to stabilize after + * reprogramming the SDRC when switching to a slower MPU speed + * */ ENTRY(omap3_sram_configure_core_dpll) stmfd sp!, {r1-r12, lr} @ store regs to stack ldr r4, [sp, #52] @ pull extra args off the stack + ldr r5, [sp, #56] @ load extra args from the stack dsb @ flush buffered writes to interconnect cmp r3, #0x2 blne configure_sdrc @@ -59,7 +63,11 @@ ENTRY(omap3_sram_configure_core_dpll) bleq wait_dll_unlock blne wait_dll_lock cmp r3, #0x1 - blne configure_sdrc + beq return_to_sdram + bl configure_sdrc + mov r12, r5 @ if slowing, wait for SDRC to stabilize + bl wait_clk_stable +return_to_sdram: isb @ prevent speculative exec past here mov r0, #0 @ return value ldmfd sp!, {r1-r12, pc} @ restore regs and return @@ -106,16 +114,6 @@ configure_core_dpll: wait_clk_stable: subs r12, r12, #1 bne wait_clk_stable - nop - nop - nop - nop - nop - nop - nop - nop - nop - nop bx lr enable_sdrc: ldr r11, omap3_cm_iclken1_core |