From 4519c2bf433b97d091635eb51e4ba8ffa1c84d62 Mon Sep 17 00:00:00 2001 From: Paul Walmsley Date: Tue, 12 May 2009 17:26:32 -0600 Subject: OMAP3 clock: only unlock SDRC DLL if SDRC clk < 83MHz According to the 34xx TRM Rev. K section 11.2.4.4.11.1 "Purpose of the DLL/CDL Module," the SDRC delay-locked-loop can be locked at any SDRC clock frequency from 83MHz to 166MHz. CDP code unconditionally unlocked the DLL whenever shifting to a lower SDRC speed, but this seems unnecessary and error-prone, as the DLL is no longer able to compensate for process, voltage, and temperature variations. Instead, only unlock the DLL when the SDRC clock rate would be less than 83MHz. Signed-off-by: Paul Walmsley --- arch/arm/mach-omap2/sram34xx.S | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'arch/arm/mach-omap2/sram34xx.S') diff --git a/arch/arm/mach-omap2/sram34xx.S b/arch/arm/mach-omap2/sram34xx.S index 35131e5bc7d..c080c82521e 100644 --- a/arch/arm/mach-omap2/sram34xx.S +++ b/arch/arm/mach-omap2/sram34xx.S @@ -40,22 +40,23 @@ /* * Change frequency of core dpll * 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 */ 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 dsb @ flush buffered writes to interconnect cmp r3, #0x2 blne configure_sdrc - cmp r3, #0x2 + cmp r4, #0x1 + bleq unlock_dll blne lock_dll - cmp r3, #0x1 - blne unlock_dll bl sdram_in_selfrefresh @ put the SDRAM in self refresh bl configure_core_dpll bl enable_sdrc - cmp r3, #0x1 - blne wait_dll_unlock - cmp r3, #0x2 + cmp r4, #0x1 + bleq wait_dll_unlock blne wait_dll_lock cmp r3, #0x1 blne configure_sdrc -- cgit v1.2.3-18-g5258