[v3] iio: adc: add buffering support to the TI LMP92064 ADC driver

  Enable buffered reading of samples from the LMP92064 ADC.
The main benefit of this change is being able to read out current and
voltage measurements in a single transfer, allowing instantaneous power
measurements.

Reads into the buffer can be triggered by any software triggers, e.g.
the iio-trig-hrtimer:

    $ mkdir /sys/kernel/config/iio/triggers/hrtimer/my-trigger
    $ cat /sys/bus/iio/devices/iio\:device3/name
    lmp92064
    $ iio_readdev -t my-trigger -b 16 iio:device3 | hexdump
    WARNING: High-speed mode not enabled
    0000000 0000 0176 0101 0001 5507 abd5 7645 1768
    0000010 0000 016d 0101 0001 ee1e ac6b 7645 1768
    ...

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
---
Changes v1->v2:

  - Remove superfluous .shift = 0 initialization in scan_type.
  - Replace kmalloc buffer allocation for every read with a stack
    allocated structure.
    A struct is used to ensure correct alignment of the timestamp field.
    See e.g. adc/rockchip_saradc.c for other users of the same pattern.
  - Use available_scan_masks and always push both voltage and current
    measurements to the buffer.

Changes v2->v3:

  - Handle errors returned by lmp92064_read_meas() out-of-line via
    a goto err;

---
 drivers/iio/adc/ti-lmp92064.c | 51 +++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)


base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1
  

Hi Leonard,

LGTM, only one comment from me. See below...
On Mon, 2023-07-03 at 12:39 +0200, Leonard Göhrs wrote:
> Enable buffered reading of samples from the LMP92064 ADC.
> The main benefit of this change is being able to read out current and
> voltage measurements in a single transfer, allowing instantaneous power
> measurements.
> 
> Reads into the buffer can be triggered by any software triggers, e.g.
> the iio-trig-hrtimer:
> 
>     $ mkdir /sys/kernel/config/iio/triggers/hrtimer/my-trigger
>     $ cat /sys/bus/iio/devices/iio\:device3/name
>     lmp92064
>     $ iio_readdev -t my-trigger -b 16 iio:device3 | hexdump
>     WARNING: High-speed mode not enabled
>     0000000 0000 0176 0101 0001 5507 abd5 7645 1768
>     0000010 0000 016d 0101 0001 ee1e ac6b 7645 1768
>     ...
> 
> Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
> ---
> Changes v1->v2:
> 
>   - Remove superfluous .shift = 0 initialization in scan_type.
>   - Replace kmalloc buffer allocation for every read with a stack
>     allocated structure.
>     A struct is used to ensure correct alignment of the timestamp field.
>     See e.g. adc/rockchip_saradc.c for other users of the same pattern.
>   - Use available_scan_masks and always push both voltage and current
>     measurements to the buffer.
> 
> Changes v2->v3:
> 
>   - Handle errors returned by lmp92064_read_meas() out-of-line via
>     a goto err;
> 
> ---
>  drivers/iio/adc/ti-lmp92064.c | 51 +++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 
> diff --git a/drivers/iio/adc/ti-lmp92064.c b/drivers/iio/adc/ti-lmp92064.c
> index c30ed824924f3..73504a27a8e22 100644
> --- a/drivers/iio/adc/ti-lmp92064.c
> +++ b/drivers/iio/adc/ti-lmp92064.c
> @@ -16,7 +16,10 @@
>  #include <linux/spi/spi.h>
>  
>  #include <linux/iio/iio.h>
> +#include <linux/iio/buffer.h>
>  #include <linux/iio/driver.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/iio/trigger_consumer.h>
>  
>  #define TI_LMP92064_REG_CONFIG_A 0x0000
>  #define TI_LMP92064_REG_CONFIG_B 0x0001
> @@ -91,6 +94,12 @@ static const struct iio_chan_spec lmp92064_adc_channels[] = {
>                 .address = TI_LMP92064_CHAN_INC,
>                 .info_mask_separate =
>                         BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +               .scan_index = TI_LMP92064_CHAN_INC,
> +               .scan_type = {
> +                       .sign = 'u',
> +                       .realbits = 12,
> +                       .storagebits = 16,
> +               },
>                 .datasheet_name = "INC",
>         },
>         {
> @@ -98,8 +107,20 @@ static const struct iio_chan_spec lmp92064_adc_channels[] = {
>                 .address = TI_LMP92064_CHAN_INV,
>                 .info_mask_separate =
>                         BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +               .scan_index = TI_LMP92064_CHAN_INV,
> +               .scan_type = {
> +                       .sign = 'u',
> +                       .realbits = 12,
> +                       .storagebits = 16,
> +               },
>                 .datasheet_name = "INV",
>         },
> +       IIO_CHAN_SOFT_TIMESTAMP(2),
> +};
> +
> +static const unsigned long lmp92064_scan_masks[] = {
> +       BIT(TI_LMP92064_CHAN_INC) | BIT(TI_LMP92064_CHAN_INV),
> +       0
>  };
>  
>  static int lmp92064_read_meas(struct lmp92064_adc_priv *priv, u16 *res)
> @@ -171,6 +192,30 @@ static int lmp92064_read_raw(struct iio_dev *indio_dev,
>         }
>  }
>  
> +static irqreturn_t lmp92064_trigger_handler(int irq, void *p)
> +{
> +       struct iio_poll_func *pf = p;
> +       struct iio_dev *indio_dev = pf->indio_dev;
> +       struct lmp92064_adc_priv *priv = iio_priv(indio_dev);
> +       struct {
> +               u16 values[2];
> +               int64_t timestamp;
> +       } data;
> +       int ret;
> +

I think you need to explicitly __align(8) your timestamp data. The reason is that
(IIRC) for x86 32 bits, a long long is not naturally aligned to 64bits but 32.

You also need to explicitly memset(0) your data so we don't leak data to userspace.

- Nuno Sá