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mfd: ti_am335x_tscadc: Don't read back REG_SE

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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 <[email protected]>
Acked-by: Dmitry Torokhov <[email protected]>
Acked-by: Jonathan Cameron <[email protected]>
Signed-off-by: Lee Jones <[email protected]>
This commit is contained in:
Sebastian Andrzej Siewior 2013-12-19 16:28:29 +01:00 • committed by Lee Jones
commit 7e170c6e4f
4 changed files with 18 additions and 9 deletions
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4
drivers/iio/adc/ti_am335x_adc.c
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@ -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) {