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>

4 files changed, 18 insertions, 9 deletions

diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
index ce8d03ac900f..95eef8e89979 100644
--- a/drivers/iio/adc/ti_am335x_adc.c
+++ b/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) {
diff --git a/drivers/input/touchscreen/ti_am335x_tsc.c b/drivers/input/touchscreen/ti_am335x_tsc.c
index 68beadaabceb..2ca5a7bee04e 100644
--- a/drivers/input/touchscreen/ti_am335x_tsc.c
+++ b/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;
diff --git a/drivers/mfd/ti_am335x_tscadc.c b/drivers/mfd/ti_am335x_tscadc.c
index 67d0eb469a45..cb0c211fc7d8 100644
--- a/drivers/mfd/ti_am335x_tscadc.c
+++ b/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);
diff --git a/include/linux/mfd/ti_am335x_tscadc.h b/include/linux/mfd/ti_am335x_tscadc.h
index 1fe72199e670..2fa9c0613da4 100644
--- a/include/linux/mfd/ti_am335x_tscadc.h
+++ b/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