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>

1 files changed, 12 insertions, 4 deletions

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);