mfd: ti_am335x_tscadc: Remove unwanted reg_se_cache save

In one shot mode, sequencer automatically disables all enabled steps at
the end of each cycle. (both ADC steps and TSC steps) Hence these steps
need not be saved in reg_se_cache for clearing these steps at a later
stage.
Also, when ADC wakes up Sequencer should not be busy executing any of the
config steps except for the charge step. Previously charge step was 1 ADC
clock cycle and hence it was ignored.
TSC steps are always disabled at the end of each conversion cycle, hence
there is no need to explicitly disable TSC steps by writing 0 to REG_SE.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/ti_am335x_tscadc.c

@@ -68,12 +68,6 @@ static void am335x_tscadc_need_adc(struct ti_tscadc_dev *tsadc)
 	DEFINE_WAIT(wait);
 	u32 reg;
 
-	/*
-	 * disable TSC steps so it does not run while the ADC is using it. If
-	 * write 0 while it is running (it just started or was already running)
-	 * then it completes all steps that were enabled and stops then.
-	 */
-	tscadc_writel(tsadc, REG_SE, 0);
 	reg = tscadc_readl(tsadc, REG_ADCFSM);
 	if (reg & SEQ_STATUS) {
 		tsadc->adc_waiting = true;
@@ -86,8 +80,12 @@ static void am335x_tscadc_need_adc(struct ti_tscadc_dev *tsadc)
 		spin_lock_irq(&tsadc->reg_lock);
 		finish_wait(&tsadc->reg_se_wait, &wait);
 
+		/*
+		 * Sequencer should either be idle or
+		 * busy applying the charge step.
+		 */
 		reg = tscadc_readl(tsadc, REG_ADCFSM);
-		WARN_ON(reg & SEQ_STATUS);
+		WARN_ON((reg & SEQ_STATUS) && !(reg & CHARGE_STEP));
 		tsadc->adc_waiting = false;
 	}
 	tsadc->adc_in_use = true;
@@ -96,7 +94,6 @@ static void am335x_tscadc_need_adc(struct ti_tscadc_dev *tsadc)
 void am335x_tsc_se_set_once(struct ti_tscadc_dev *tsadc, u32 val)
 {
 	spin_lock_irq(&tsadc->reg_lock);
-	tsadc->reg_se_cache |= val;
 	am335x_tscadc_need_adc(tsadc);
 
 	tscadc_writel(tsadc, REG_SE, val);

include/linux/mfd/ti_am335x_tscadc.h

@@ -128,6 +128,7 @@
 
 /* Sequencer Status */
 #define SEQ_STATUS BIT(5)
+#define CHARGE_STEP		0x11
 
 #define ADC_CLK			3000000
 #define TOTAL_STEPS		16