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 <paul@pwsan.com>
diff --git a/arch/arm/mach-omap2/clock34xx.c b/arch/arm/mach-omap2/clock34xx.c
index 0a14dca..811360a 100644
--- a/arch/arm/mach-omap2/clock34xx.c
+++ b/arch/arm/mach-omap2/clock34xx.c
@@ -281,6 +281,8 @@
#define MAX_DPLL_WAIT_TRIES 1000000
+#define MIN_SDRC_DLL_LOCK_FREQ 83000000
+
/**
* omap3_dpll_recalc - recalculate DPLL rate
* @clk: DPLL struct clk
@@ -703,6 +705,7 @@
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;
struct omap_sdrc_params *sp;
@@ -729,6 +732,11 @@
if (!sp)
return -EINVAL;
+ if (sdrcrate < MIN_SDRC_DLL_LOCK_FREQ) {
+ pr_debug("clock: will unlock SDRC DLL\n");
+ unlock_dll = 1;
+ }
+
pr_info("clock: changing CORE DPLL rate from %lu to %lu\n", clk->rate,
validrate);
pr_info("clock: SDRC timing params used: %08x %08x %08x\n",
@@ -739,7 +747,7 @@
/* REVISIT: Add SDRC_MR changing to this code also */
omap3_configure_core_dpll(sp->rfr_ctrl, sp->actim_ctrla,
- sp->actim_ctrlb, new_div);
+ sp->actim_ctrlb, new_div, unlock_dll);
return 0;
}