On 12/19/13 15:28, Sebastian Andrzej Siewior wrote:
> 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 becoming interrupts even if nobody
becoming -> generating?
> 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.
>
yikes.
> 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.
>
Thanks for the detailed explanation.
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Hmm. I'm not really an expert in this complex driver, but your explanation is clear
and the code appears to implement what you describe. Hopefully we'll see a fix for
the continuous reads as well.
Fiddly little device!
Acked-by: Jonathan Cameron <jic23@xxxxxxxxxx>
> ---
> drivers/iio/adc/ti_am335x_adc.c | 64 ++++++++++++++++++++++++++----------
> drivers/mfd/ti_am335x_tscadc.c | 63 +++++++++++++++++++++++++++++------
> include/linux/mfd/ti_am335x_tscadc.h | 4 +++
> 3 files changed, 103 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
> index 6822b9f..31e786e 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];
> @@ -329,34 +347,43 @@ 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;
> @@ -368,6 +395,7 @@ 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;
> @@ -495,8 +523,8 @@ 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;
> }
>
> diff --git a/drivers/mfd/ti_am335x_tscadc.c b/drivers/mfd/ti_am335x_tscadc.c
> index 157f569..d4e8604 100644
> --- a/drivers/mfd/ti_am335x_tscadc.c
> +++ b/drivers/mfd/ti_am335x_tscadc.c
> @@ -24,6 +24,7 @@
> #include <linux/pm_runtime.h>
> #include <linux/of.h>
> #include <linux/of_device.h>
> +#include <linux/sched.h>
>
> #include <linux/mfd/ti_am335x_tscadc.h>
>
> @@ -48,31 +49,71 @@ static const struct regmap_config tscadc_regmap_config = {
> .val_bits = 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_cache(struct ti_tscadc_dev *tsadc, u32 val)
> {
> unsigned long flags;
>
> spin_lock_irqsave(&tsadc->reg_lock, flags);
> - tsadc->reg_se_cache |= val;
> - am335x_tsc_se_update(tsadc);
> + tsadc->reg_se_cache = val;
> + if (tsadc->adc_waiting)
> + wake_up(&tsadc->reg_se_wait);
> + else if (!tsadc->adc_in_use)
> + tscadc_writel(tsadc, REG_SE, val);
> +
> spin_unlock_irqrestore(&tsadc->reg_lock, flags);
> }
> EXPORT_SYMBOL_GPL(am335x_tsc_se_set_cache);
>
> +static void am335x_tscadc_need_adc(struct ti_tscadc_dev *tsadc)
> +{
> + DEFINE_WAIT(wait);
> + u32 reg;
> +
> + /*
> + * disable TSC steps so it does not run while the ADC is using it. If
> + * write 0 while it is running (it just started or was already running)
> + * then it completes all steps that were enabled and stops then.
> + */
> + tscadc_writel(tsadc, REG_SE, 0);
> + reg = tscadc_readl(tsadc, REG_ADCFSM);
> + if (reg & SEQ_STATUS) {
> + tsadc->adc_waiting = true;
> + prepare_to_wait(&tsadc->reg_se_wait, &wait,
> + TASK_UNINTERRUPTIBLE);
> + spin_unlock_irq(&tsadc->reg_lock);
> +
> + schedule();
> +
> + spin_lock_irq(&tsadc->reg_lock);
> + finish_wait(&tsadc->reg_se_wait, &wait);
> +
> + reg = tscadc_readl(tsadc, REG_ADCFSM);
> + WARN_ON(reg & SEQ_STATUS);
> + tsadc->adc_waiting = false;
> + }
> + tsadc->adc_in_use = true;
> +}
> +
> void am335x_tsc_se_set_once(struct ti_tscadc_dev *tsadc, u32 val)
> {
> + spin_lock_irq(&tsadc->reg_lock);
> + am335x_tscadc_need_adc(tsadc);
> +
> + tscadc_writel(tsadc, REG_SE, val);
> + spin_unlock_irq(&tsadc->reg_lock);
> +}
> +EXPORT_SYMBOL_GPL(am335x_tsc_se_set_once);
> +
> +void am335x_tsc_se_adc_done(struct ti_tscadc_dev *tsadc)
> +{
> unsigned long flags;
>
> spin_lock_irqsave(&tsadc->reg_lock, flags);
> - tscadc_writel(tsadc, REG_SE, tsadc->reg_se_cache | val);
> + tsadc->adc_in_use = false;
> + tscadc_writel(tsadc, REG_SE, tsadc->reg_se_cache);
> spin_unlock_irqrestore(&tsadc->reg_lock, flags);
> }
> -EXPORT_SYMBOL_GPL(am335x_tsc_se_set_once);
> +EXPORT_SYMBOL_GPL(am335x_tsc_se_adc_done);
>
> void am335x_tsc_se_clr(struct ti_tscadc_dev *tsadc, u32 val)
> {
> @@ -80,7 +121,7 @@ void am335x_tsc_se_clr(struct ti_tscadc_dev *tsadc, u32 val)
>
> spin_lock_irqsave(&tsadc->reg_lock, flags);
> tsadc->reg_se_cache &= ~val;
> - am335x_tsc_se_update(tsadc);
> + tscadc_writel(tsadc, REG_SE, tsadc->reg_se_cache);
> spin_unlock_irqrestore(&tsadc->reg_lock, flags);
> }
> EXPORT_SYMBOL_GPL(am335x_tsc_se_clr);
> @@ -188,6 +229,8 @@ static int ti_tscadc_probe(struct platform_device *pdev)
> }
>
> spin_lock_init(&tscadc->reg_lock);
> + init_waitqueue_head(&tscadc->reg_se_wait);
> +
> pm_runtime_enable(&pdev->dev);
> pm_runtime_get_sync(&pdev->dev);
>
> diff --git a/include/linux/mfd/ti_am335x_tscadc.h b/include/linux/mfd/ti_am335x_tscadc.h
> index 2fa9c06..fb96c84 100644
> --- a/include/linux/mfd/ti_am335x_tscadc.h
> +++ b/include/linux/mfd/ti_am335x_tscadc.h
> @@ -159,6 +159,9 @@ struct ti_tscadc_dev {
> int adc_cell; /* -1 if not used */
> struct mfd_cell cells[TSCADC_CELLS];
> u32 reg_se_cache;
> + bool adc_waiting;
> + bool adc_in_use;
> + wait_queue_head_t reg_se_wait;
> spinlock_t reg_lock;
> unsigned int clk_div;
>
> @@ -179,5 +182,6 @@ static inline struct ti_tscadc_dev *ti_tscadc_dev_get(struct platform_device *p)
> 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);
> +void am335x_tsc_se_adc_done(struct ti_tscadc_dev *tsadc);
>
> #endif
>
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