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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2013-12-19 16:28:31 +0100
committerLee Jones <lee.jones@linaro.org>2014-01-07 08:45:00 +0000
commit7ca6740cd1cd410828a01151a044b51910d06eff (patch)
treee9527767fefbe621dfdeca70e0a310c818f9175d /drivers/iio/adc
parent3954b7bfc665fed878cabe57342bae34d2391478 (diff)
mfd: input: iio: ti_amm335x: Rework TSC/ADC synchronization
The ADC driver always programs all possible ADC values and discards them except for the value IIO asked for. On the am335x-evm the driver programs four values and it takes 500us to gather them. Reducing the number of conversations down to the (required) one also reduces the busy loop down to 125us. This leads to another error, namely the FIFOCOUNT register is sometimes (like one out of 10 attempts) not updated in time leading to EBUSY. The next read has the FIFOCOUNT register updated. Checking for the ADCSTAT register for being idle isn't a good choice either. The problem is that if TSC is used at the same time, the HW completes the conversation for ADC *and* before the driver noticed it, the HW begins to perform a TSC conversation and so the driver never seen the HW idle. The next time we would have two values in the FIFO but since the driver reads everything we always see the current one. So instead of polling for the IDLE bit in ADCStatus register, we should check the FIFOCOUNT register. It should be one instead of zero because we request one value. This change in turn leads to another error. Sometimes if TSC & ADC are used together the TSC starts generating interrupts even if nobody actually touched the touchscreen. The interrupts seem valid because TSC's FIFO is filled with values for each channel of the TSC. This condition stops after a few ADC reads but will occur again. Not good. On top of this (even without the changes I just mentioned) there is a ADC & TSC lockup condition which was reported to me by Jeff Lance including the following test case: A busy loop of "cat /sys/bus/iio/devices/iio\:device0/in_voltage4_raw" and a mug on touch screen. With this setup, the hardware will lockup after something between 20 minutes and it could take up to a couple of hours. During that lockup, the ADCSTAT register says 0x30 (or 0x70) which means STEP_ID = IDLE and FSM_BUSY = yes. That means the hardware says that it is idle and busy at the same time which is an invalid condition. For all this reasons I decided to rework this TSC/ADC part and add a handshake / synchronization here: First the ADC signals that it needs the HW and writes a 0 mask into the SE register. The HW (if active) will complete the current conversation and become idle. The TSC driver will gather the values from the FIFO (woken up by an interrupt) and won't "enable" another conversation. Instead it will wake up the ADC driver which is already waiting. The ADC driver will start "its" conversation and once it is done, it will enable the TSC steps so the TSC will work again. After this rework I haven't observed the lockup so far. Plus the busy loop has been reduced from 500us to 125us. The continues-read mode remains unchanged. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Jonathan Cameron <jic23@kernel.org> Signed-off-by: Lee Jones <lee.jones@linaro.org>
Diffstat (limited to 'drivers/iio/adc')
-rw-r--r--drivers/iio/adc/ti_am335x_adc.c64
1 files changed, 46 insertions, 18 deletions
diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
index e0dc2d0e7590..dff7343405e2 100644
--- a/drivers/iio/adc/ti_am335x_adc.c
+++ b/drivers/iio/adc/ti_am335x_adc.c
@@ -60,6 +60,24 @@ static u32 get_adc_step_mask(struct tiadc_device *adc_dev)
return step_en;
}
+static u32 get_adc_chan_step_mask(struct tiadc_device *adc_dev,
+ struct iio_chan_spec const *chan)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(adc_dev->channel_step); i++) {
+ if (chan->channel == adc_dev->channel_line[i]) {
+ u32 step;
+
+ step = adc_dev->channel_step[i];
+ /* +1 for the charger */
+ return 1 << (step + 1);
+ }
+ }
+ WARN_ON(1);
+ return 0;
+}
+
static u32 get_adc_step_bit(struct tiadc_device *adc_dev, int chan)
{
return 1 << adc_dev->channel_step[chan];
@@ -326,34 +344,43 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
unsigned int fifo1count, read, stepid;
bool found = false;
u32 step_en;
- unsigned long timeout = jiffies + usecs_to_jiffies
- (IDLE_TIMEOUT * adc_dev->channels);
+ unsigned long timeout;
if (iio_buffer_enabled(indio_dev))
return -EBUSY;
- step_en = get_adc_step_mask(adc_dev);
+ step_en = get_adc_chan_step_mask(adc_dev, chan);
+ if (!step_en)
+ return -EINVAL;
+
+ fifo1count = tiadc_readl(adc_dev, REG_FIFO1CNT);
+ while (fifo1count--)
+ tiadc_readl(adc_dev, REG_FIFO1);
+
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) {
- if (time_after(jiffies, timeout))
+ timeout = jiffies + usecs_to_jiffies
+ (IDLE_TIMEOUT * adc_dev->channels);
+ /* Wait for Fifo threshold interrupt */
+ while (1) {
+ fifo1count = tiadc_readl(adc_dev, REG_FIFO1CNT);
+ if (fifo1count)
+ break;
+
+ if (time_after(jiffies, timeout)) {
+ am335x_tsc_se_adc_done(adc_dev->mfd_tscadc);
return -EAGAIN;
+ }
}
map_val = chan->channel + TOTAL_CHANNELS;
/*
- * When the sub-system is first enabled,
- * the sequencer will always start with the
- * lowest step (1) and continue until step (16).
- * For ex: If we have enabled 4 ADC channels and
- * currently use only 1 out of them, the
- * sequencer still configures all the 4 steps,
- * leading to 3 unwanted data.
- * Hence we need to flush out this data.
+ * We check the complete FIFO. We programmed just one entry but in case
+ * something went wrong we left empty handed (-EAGAIN previously) and
+ * then the value apeared somehow in the FIFO we would have two entries.
+ * Therefore we read every item and keep only the latest version of the
+ * requested channel.
*/
-
- fifo1count = tiadc_readl(adc_dev, REG_FIFO1CNT);
for (i = 0; i < fifo1count; i++) {
read = tiadc_readl(adc_dev, REG_FIFO1);
stepid = read & FIFOREAD_CHNLID_MASK;
@@ -365,6 +392,7 @@ static int tiadc_read_raw(struct iio_dev *indio_dev,
*val = (u16) read;
}
}
+ am335x_tsc_se_adc_done(adc_dev->mfd_tscadc);
if (found == false)
return -EBUSY;
@@ -492,8 +520,8 @@ static int tiadc_resume(struct device *dev)
tiadc_writel(adc_dev, REG_CTRL, restore);
tiadc_step_config(indio_dev);
- am335x_tsc_se_set(adc_dev->mfd_tscadc, adc_dev->buffer_en_ch_steps);
-
+ am335x_tsc_se_set_cache(adc_dev->mfd_tscadc,
+ adc_dev->buffer_en_ch_steps);
return 0;
}