Subject: Re: [PATCH v2 2/3] iio: adc: at91-sama5d2_adc: handle unfinished conversions

From: <[email-masked]>
Date: Mon, 20 Jan 2020 07:27:00 +0000

On 17.01.2020 19:34, Jonathan Cameron wrote:

> On Mon, 13 Jan 2020 12:07:09 +0000
> <[email-masked]> wrote:
> 
>> From: Eugen Hristev <[email-masked]>
>>
>> It can happen that on IRQ trigger, not all conversions are done if
>> we are enabling multiple channels.
>> The IRQ is triggered on first EOC (end of channel), but it can happen
>> that not all channels are done. This leads into erroneous reports to
>> userspace (zero values or previous values).
>> To solve this, in trigger handler, check if the mask of done channels
>> is the same as the mask of active scan channels.
>> If it's the same, proceed and push to buffers. Otherwise, use usleep
>> to sleep until the conversion is done or we timeout.
>> Normally, it should happen that in a short time fashion, all channels are
>> ready, since the first IRQ triggered.
>> If a hardware fault happens (for example the clock suddently dissappears),
>> the handler will not be completed, in which case we do not report anything to
>> userspace anymore.
>> Also, change from using the EOC interrupts to DRDY interrupt.
>> This helps with the fact that not 'n' interrupt statuses are enabled,
>> each being able to trigger an interrupt, and instead only data ready
>> interrupt can wake up the CPU. Like this, when data is ready, check in
>> handler which and how many channels are done. While the DRDY is raised,
>> other IRQs cannot occur. Once the channel data is being read, we ack the
>> IRQ and finish the conversion.
>>
>> Signed-off-by: Eugen Hristev <[email-masked]>
>> ---
>> Changes in v2:
>> - move start of conversion to threaded irq, removed specific at91 pollfunc
>> - add timeout to channel mask readiness check in trigger handler
>> - use DRDY irq instead of EOC irqs.
>> - move enable irq after DRDY has been acked in reenable_trigger
>>
>>   drivers/iio/adc/at91-sama5d2_adc.c | 62 ++++++++++++++++++++++++++++----------
>>   1 file changed, 46 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
>> index 2a6950a..454a493 100644
>> --- a/drivers/iio/adc/at91-sama5d2_adc.c
>> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
>> @@ -8,6 +8,7 @@
>>
>>   #include <linux/bitops.h>
>>   #include <linux/clk.h>
>> +#include <linux/delay.h>
>>   #include <linux/dma-mapping.h>
>>   #include <linux/dmaengine.h>
>>   #include <linux/interrupt.h>
>> @@ -100,6 +101,8 @@
>>   #define AT91_SAMA5D2_IER_YRDY   BIT(21)
>>   /* Interrupt Enable Register - TS pressure measurement ready */
>>   #define AT91_SAMA5D2_IER_PRDY   BIT(22)
>> +/* Interrupt Enable Register - Data ready */
>> +#define AT91_SAMA5D2_IER_DRDY   BIT(24)
>>   /* Interrupt Enable Register - general overrun error */
>>   #define AT91_SAMA5D2_IER_GOVRE BIT(25)
>>   /* Interrupt Enable Register - Pen detect */
>> @@ -486,6 +489,21 @@ static inline int at91_adc_of_xlate(struct iio_dev *indio_dev,
>>        return at91_adc_chan_xlate(indio_dev, iiospec->args[0]);
>>   }
>>
>> +static unsigned int at91_adc_active_scan_mask_to_reg(struct iio_dev *indio_dev)
>> +{
>> +     u32 mask = 0;
>> +     u8 bit;
>> +
>> +     for_each_set_bit(bit, indio_dev->active_scan_mask,
>> +                      indio_dev->num_channels) {
>> +             struct iio_chan_spec const *chan =
>> +                      at91_adc_chan_get(indio_dev, bit);
>> +             mask |= BIT(chan->channel);
>> +     }
>> +
>> +     return mask & GENMASK(11, 0);
>> +}
>> +
>>   static void at91_adc_config_emr(struct at91_adc_state *st)
>>   {
>>        /* configure the extended mode register */
>> @@ -746,24 +764,19 @@ static int at91_adc_configure_trigger(struct iio_trigger *trig, bool state)
>>                        at91_adc_writel(st, AT91_SAMA5D2_COR, cor);
>>                }
>>
>> -             if (state) {
>> +             if (state)
>>                        at91_adc_writel(st, AT91_SAMA5D2_CHER,
>>                                        BIT(chan->channel));
>> -                     /* enable irq only if not using DMA */
>> -                     if (!st->dma_st.dma_chan) {
>> -                             at91_adc_writel(st, AT91_SAMA5D2_IER,
>> -                                             BIT(chan->channel));
>> -                     }
>> -             } else {
>> -                     /* disable irq only if not using DMA */
>> -                     if (!st->dma_st.dma_chan) {
>> -                             at91_adc_writel(st, AT91_SAMA5D2_IDR,
>> -                                             BIT(chan->channel));
>> -                     }
>> +             else
>>                        at91_adc_writel(st, AT91_SAMA5D2_CHDR,
>>                                        BIT(chan->channel));
>> -             }
>>        }
>> +     /* enable irq only if not using DMA */
>> +     if (state && !st->dma_st.dma_chan)
>> +             at91_adc_writel(st, AT91_SAMA5D2_IER, AT91_SAMA5D2_IER_DRDY);
>> +     /* disable irq only if not using DMA */
>> +     if (!state && !st->dma_st.dma_chan)
>> +             at91_adc_writel(st, AT91_SAMA5D2_IDR, AT91_SAMA5D2_IER_DRDY);
> Hmm. Would have been nicer to avoid the refactor and just have the change to
> what was written. If you want to keep it, perhaps:
> 
>          /* Nothing to do if using DMA */
>          if (!st->dma_st.dma_chan)
>                  return 0;
> 
>          if (state)
>                  at91...
>          else
>                  at91...
> 

Hi Jonathan,

Ok I will rework it in next version

>>
>>        return 0;
>>   }
>> @@ -777,10 +790,10 @@ static int at91_adc_reenable_trigger(struct iio_trigger *trig)
>>        if (st->dma_st.dma_chan)
>>                return 0;
>>
>> -     enable_irq(st->irq);
>> -
>>        /* Needed to ACK the DRDY interruption */
>>        at91_adc_readl(st, AT91_SAMA5D2_LCDR);
>> +
>> +     enable_irq(st->irq);
> 
> Why this change?  I'm not totally following the description above.
> 

The ' reading of the LCDR register ' makes the DRDY bit in ISR 
(interrupt status register) to be cleared.
So, reading that clears the IRQ, but, if we enable the IRQs before this 
clearance, there is a race chance that we get the DRDY IRQ triggered again.
It is best to clear the DRDY first, and then re enable the IRQs.

Does it make sense ?

>>        return 0;
>>   }
>>
>> @@ -1015,6 +1028,22 @@ static void at91_adc_trigger_handler_nodma(struct iio_dev *indio_dev,
>>        int i = 0;
>>        int val;
>>        u8 bit;
>> +     u32 mask = at91_adc_active_scan_mask_to_reg(indio_dev);
>> +     unsigned int timeout = 50;
>> +
>> +     /*
>> +      * Check if the conversion is ready. If not, wait a little bit, and
>> +      * in case of timeout exit with an error.
>> +      */
>> +     while ((at91_adc_readl(st, AT91_SAMA5D2_ISR) & mask) != mask &&
>> +            timeout) {
>> +             usleep_range(50, 100);
>> +             timeout--;
>> +     }
>> +
>> +     /* Cannot read data, not ready. Continue without reporting data */
>> +     if (!timeout)
>> +             return;
>>
>>        for_each_set_bit(bit, indio_dev->active_scan_mask,
>>                         indio_dev->num_channels) {
>> @@ -1281,7 +1310,8 @@ static irqreturn_t at91_adc_interrupt(int irq, void *private)
>>                status = at91_adc_readl(st, AT91_SAMA5D2_XPOSR);
>>                status = at91_adc_readl(st, AT91_SAMA5D2_YPOSR);
>>                status = at91_adc_readl(st, AT91_SAMA5D2_PRESSR);
>> -     } else if (iio_buffer_enabled(indio) && !st->dma_st.dma_chan) {
>> +     } else if (iio_buffer_enabled(indio) &&
>> +                (status & AT91_SAMA5D2_IER_DRDY)) {
>>                /* triggered buffer without DMA */
>>                disable_irq_nosync(irq);
>>                iio_trigger_poll(indio->trig);
> 
> 
> 
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