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>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/arm/plat-omap/sram.c b/arch/arm/plat-omap/sram.c
index a5b9bcd6b108..79c0f0254426 100644
--- a/arch/arm/plat-omap/sram.c
+++ b/arch/arm/plat-omap/sram.c
@@ -371,15 +371,17 @@ static inline int omap243x_sram_init(void)
 static u32 (*_omap3_sram_configure_core_dpll)(u32 sdrc_rfr_ctrl,
                                               u32 sdrc_actim_ctrla,
                                               u32 sdrc_actim_ctrlb,
-                                              u32 m2, u32 unlock_dll);
+                                              u32 m2, u32 unlock_dll,
+                                              u32 f);
 u32 omap3_configure_core_dpll(u32 sdrc_rfr_ctrl, u32 sdrc_actim_ctrla,
-                              u32 sdrc_actim_ctrlb, u32 m2, u32 unlock_dll)
+                              u32 sdrc_actim_ctrlb, u32 m2, u32 unlock_dll,
+                              u32 f)
 {
         BUG_ON(!_omap3_sram_configure_core_dpll);
         return _omap3_sram_configure_core_dpll(sdrc_rfr_ctrl,
                                                sdrc_actim_ctrla,
                                                sdrc_actim_ctrlb, m2,
-                                               unlock_dll);
+                                               unlock_dll, f);
 }
 
 /* REVISIT: Should this be same as omap34xx_sram_init() after off-idle? */