mfd: ti_am335x_tscadc: Don't read back REG_SE

The purpose of reg_se_cache has been defeated. It should avoid the
read-back of the register to avoid the latency and the fact that the
bits are reset to 0 after the individual conversation took place.

The reason why this is required like this to work, is that read-back of
the register removes the bits of the ADC so they do not start another
conversation after the register is re-written from the TSC side for the
update.
To avoid the not required read-back I introduce a "set once" variant which
does not update the cache mask. After the conversation completes, the
bit is removed from the SE register anyway and we don't plan a new
conversation "any time soon". The current set function is renamed to
set_cache to distinguish the two operations.
This is a small preparation for a larger sync-rework.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/iio/adc/ti_am335x_adc.c

@@ -181,7 +181,7 @@ static int tiadc_buffer_postenable(struct iio_dev *indio_dev)
 		enb |= (get_adc_step_bit(adc_dev, bit) << 1);
 	adc_dev->buffer_en_ch_steps = enb;
 
-	am335x_tsc_se_set(adc_dev->mfd_tscadc, enb);
+	am335x_tsc_se_set_cache(adc_dev->mfd_tscadc, enb);
 
 	tiadc_writel(adc_dev,  REG_IRQSTATUS, IRQENB_FIFO1THRES
 				| IRQENB_FIFO1OVRRUN | IRQENB_FIFO1UNDRFLW);
@@ -332,7 +332,7 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
 		return -EBUSY;
 
 	step_en = get_adc_step_mask(adc_dev);
-	am335x_tsc_se_set(adc_dev->mfd_tscadc, step_en);
+	am335x_tsc_se_set_once(adc_dev->mfd_tscadc, step_en);
 
 	/* Wait for ADC sequencer to complete sampling */
 	while (tiadc_readl(adc_dev, REG_ADCFSM) & SEQ_STATUS) {

drivers/input/touchscreen/ti_am335x_tsc.c

@@ -198,7 +198,7 @@ static void titsc_step_config(struct titsc *ts_dev)
 	/* The steps1 … end and bit 0 for TS_Charge */
 	stepenable = (1 << (end_step + 2)) - 1;
 	ts_dev->step_mask = stepenable;
-	am335x_tsc_se_set(ts_dev->mfd_tscadc, ts_dev->step_mask);
+	am335x_tsc_se_set_cache(ts_dev->mfd_tscadc, ts_dev->step_mask);
 }
 
 static void titsc_read_coordinates(struct titsc *ts_dev,
@@ -322,7 +322,7 @@ static irqreturn_t titsc_irq(int irq, void *dev)
 
 	if (irqclr) {
 		titsc_writel(ts_dev, REG_IRQSTATUS, irqclr);
-		am335x_tsc_se_set(ts_dev->mfd_tscadc, ts_dev->step_mask);
+		am335x_tsc_se_set_cache(ts_dev->mfd_tscadc, ts_dev->step_mask);
 		return IRQ_HANDLED;
 	}
 	return IRQ_NONE;

drivers/mfd/ti_am335x_tscadc.c

@@ -53,24 +53,32 @@ static void am335x_tsc_se_update(struct ti_tscadc_dev *tsadc)
 	tscadc_writel(tsadc, REG_SE, tsadc->reg_se_cache);
 }
 
-void am335x_tsc_se_set(struct ti_tscadc_dev *tsadc, u32 val)
+void am335x_tsc_se_set_cache(struct ti_tscadc_dev *tsadc, u32 val)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(&tsadc->reg_lock, flags);
-	tsadc->reg_se_cache = tscadc_readl(tsadc, REG_SE);
 	tsadc->reg_se_cache |= val;
 	am335x_tsc_se_update(tsadc);
 	spin_unlock_irqrestore(&tsadc->reg_lock, flags);
 }
-EXPORT_SYMBOL_GPL(am335x_tsc_se_set);
+EXPORT_SYMBOL_GPL(am335x_tsc_se_set_cache);
+
+void am335x_tsc_se_set_once(struct ti_tscadc_dev *tsadc, u32 val)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&tsadc->reg_lock, flags);
+	tscadc_writel(tsadc, REG_SE, tsadc->reg_se_cache | val);
+	spin_unlock_irqrestore(&tsadc->reg_lock, flags);
+}
+EXPORT_SYMBOL_GPL(am335x_tsc_se_set_once);
 
 void am335x_tsc_se_clr(struct ti_tscadc_dev *tsadc, u32 val)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(&tsadc->reg_lock, flags);
-	tsadc->reg_se_cache = tscadc_readl(tsadc, REG_SE);
 	tsadc->reg_se_cache &= ~val;
 	am335x_tsc_se_update(tsadc);
 	spin_unlock_irqrestore(&tsadc->reg_lock, flags);

include/linux/mfd/ti_am335x_tscadc.h

@@ -176,7 +176,8 @@ static inline struct ti_tscadc_dev *ti_tscadc_dev_get(struct platform_device *p)
 	return *tscadc_dev;
 }
 
-void am335x_tsc_se_set(struct ti_tscadc_dev *tsadc, u32 val);
+void am335x_tsc_se_set_cache(struct ti_tscadc_dev *tsadc, u32 val);
+void am335x_tsc_se_set_once(struct ti_tscadc_dev *tsadc, u32 val);
 void am335x_tsc_se_clr(struct ti_tscadc_dev *tsadc, u32 val);
 
 #endif