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

Jonathan Cameron
2020-01-17T17:34:29Z

On Mon, 13 Jan 2020 12:07:09 +0000
<Eugen.Hristev@microchip.com> wrote:

> From: Eugen Hristev <eugen.hristev@microchip.com>
>
> 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 <eugen.hristev@microchip.com>
> ---
> 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...

>
> 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.

> 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);