From c9812d042a21eb492a36cfabf9f41107f5ecee3d Mon Sep 17 00:00:00 2001 From: Paul Walmsley Date: Fri, 19 Jun 2009 19:08:26 -0600 Subject: 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 --- arch/arm/mach-omap2/clock34xx.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) (limited to 'arch/arm/mach-omap2/clock34xx.c') diff --git a/arch/arm/mach-omap2/clock34xx.c b/arch/arm/mach-omap2/clock34xx.c index 5458ab3bf65a..4bfa650bb34b 100644 --- a/arch/arm/mach-omap2/clock34xx.c +++ b/arch/arm/mach-omap2/clock34xx.c @@ -286,6 +286,20 @@ static struct omap_clk omap34xx_clks[] = { #define MIN_SDRC_DLL_LOCK_FREQ 83000000 +#define CYCLES_PER_MHZ 1000000 + +/* Scale factor for fixed-point arith in omap3_core_dpll_m2_set_rate() */ +#define SDRC_MPURATE_SCALE 8 + +/* 2^SDRC_MPURATE_BASE_SHIFT: MPU MHz that SDRC_MPURATE_LOOPS is defined for */ +#define SDRC_MPURATE_BASE_SHIFT 9 + +/* + * SDRC_MPURATE_LOOPS: Number of MPU loops to execute at + * 2^MPURATE_BASE_SHIFT MHz for SDRC to stabilize + */ +#define SDRC_MPURATE_LOOPS 96 + /** * omap3_dpll_recalc - recalculate DPLL rate * @clk: DPLL struct clk @@ -709,7 +723,8 @@ static int omap3_core_dpll_m2_set_rate(struct clk *clk, unsigned long rate) { u32 new_div = 0; u32 unlock_dll = 0; - unsigned long validrate, sdrcrate; + u32 c; + unsigned long validrate, sdrcrate, mpurate; struct omap_sdrc_params *sp; if (!clk || !rate) @@ -737,6 +752,17 @@ static int omap3_core_dpll_m2_set_rate(struct clk *clk, unsigned long rate) unlock_dll = 1; } + /* + * XXX This only needs to be done when the CPU frequency changes + */ + mpurate = arm_fck.rate / CYCLES_PER_MHZ; + c = (mpurate << SDRC_MPURATE_SCALE) >> SDRC_MPURATE_BASE_SHIFT; + c += 1; /* for safety */ + c *= SDRC_MPURATE_LOOPS; + c >>= SDRC_MPURATE_SCALE; + if (c == 0) + c = 1; + pr_debug("clock: changing CORE DPLL rate from %lu to %lu\n", clk->rate, validrate); pr_debug("clock: SDRC timing params used: %08x %08x %08x\n", @@ -747,7 +773,7 @@ static int omap3_core_dpll_m2_set_rate(struct clk *clk, unsigned long rate) /* REVISIT: Add SDRC_MR changing to this code also */ omap3_configure_core_dpll(sp->rfr_ctrl, sp->actim_ctrla, - sp->actim_ctrlb, new_div, unlock_dll); + sp->actim_ctrlb, new_div, unlock_dll, c); return 0; } -- cgit v1.2.3-59-g8ed1b