[PATCH] mfd: RK808: Add register caching

[Doug Anderson]

Let's define the voltatile registers (those that can't be cached) and
enable caching.  The rk808 is accessed almost constantly with cpufreq
so this is really nice.

As measured by ftrace:
  before this change: cpu0_set_target() => ~2200us
  after this change:  cpu0_set_target() =>  ~500us

Signed-off-by: Doug Anderson <dianders at chromium.org>
---
 drivers/mfd/rk808.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/mfd/rk808.c b/drivers/mfd/rk808.c
index 0324422..bd02150 100644
--- a/drivers/mfd/rk808.c
+++ b/drivers/mfd/rk808.c
@@ -29,10 +29,40 @@ struct rk808_reg_data {
 	int value;
 };
 
+static bool rk808_is_volatile_reg(struct device *dev, unsigned int reg)
+{
+	/*
+	 * Notes:
+	 * - Technically the ROUND_30s bit makes RTC_CTRL_REG volatile, but
+	 *   we don't use that feature.  It's better to cache.
+	 * - It's unlikely we care that RK808_DEVCTRL_REG is volatile since
+	 *   bits are cleared in case when we shutoff anyway, but better safe.
+	 */
+
+	switch (reg) {
+	case RK808_SECONDS_REG ... RK808_WEEKS_REG:
+	case RK808_RTC_STATUS_REG:
+	case RK808_VB_MON_REG:
+	case RK808_THERMAL_REG:
+	case RK808_DCDC_UV_STS_REG:
+	case RK808_LDO_UV_STS_REG:
+	case RK808_DCDC_PG_REG:
+	case RK808_LDO_PG_REG:
+	case RK808_DEVCTRL_REG:
+	case RK808_INT_STS_REG1:
+	case RK808_INT_STS_REG2:
+		return true;
+	}
+
+	return false;
+}
+
 static const struct regmap_config rk808_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = RK808_IO_POL_REG,
+	.cache_type = REGCACHE_RBTREE,
+	.volatile_reg = rk808_is_volatile_reg,
 };
 
 static struct resource rtc_resources[] = {
-- 
2.1.0.rc2.206.gedb03e5