Date:   Thu, 30 Apr 2020 08:42:37 +0000
From:   <Eugen.Hristev@...rochip.com>
To:     <alexandru.ardelean@...log.com>, <linux-iio@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <jic23@...nel.org>, <lars@...afoo.de>,
        <Ludovic.Desroches@...rochip.com>
Subject: Re: [RFC PATCH] iio: __iio_update_buffers: Update mode before
 preenable/after postdisable

On 30.04.2020 11:24, Alexandru Ardelean wrote:
> From: Lars-Peter Clausen <lars@...afoo.de>
> 
> It is clear that we transition to INDIO_DIRECT_MODE when disabling the
> buffer(s) and it is also clear that we transition from INDIO_DIRECT_MODE
> when enabling the buffer(s). So leaving the currentmode field
> INDIO_DIRECT_MODE until after the preenable() callback and updating it to
> INDIO_DIRECT_MODE before the postdisable() callback doesn't add additional
> value. On the other hand some drivers will need to perform different
> actions depending on which mode the device is going to operate in/was
> operating in.
> 
> Moving the update of currentmode before preenable() and after postdisable()
> enables us to have drivers which perform mode dependent actions in those
> callbacks.
> 
> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---
> 
> This patch is also a V2 of this older patch from a while ago:
>   https://lore.kernel.org/linux-iio/1431525891-19285-5-git-send-email-lars@metafoo.de/
> 
> However, in this recent context, it comes to fix this:
>   https://lore.kernel.org/linux-iio/b9ab676489de3575984dac5610fcf05fd8742a38.camel@analog.com/T/#mc09284c8f79250b92a52fd5b8d1f541d1c02c0c0
> 
> At this point, I don't have a clear idea if this approach is good or
> not; since the motivation is to fix the at91 adc.
> Hence the RFC.
> 
> Some excerpt from the AT91 discussion:
> -------------------------------------------------------------------
> I decided to do a bit of shell magic for this:
> 
> get_files() {
> git grep -w iio_buffer_setup_ops  | grep drivers | cut -d: -f1 | sort | uniq
> }
> 
> for file in $(get_files) ; do
>      if grep -q currentmode $file ; then
>          echo $file
>      fi
> done
> 
> It finds 4 drivers.
> Though, `get_files()` will return 56 files.
> 
> drivers/iio/accel/bmc150-accel-core.c
> drivers/iio/adc/at91-sama5d2_adc.c
> drivers/iio/adc/stm32-dfsdm-adc.c
> drivers/iio/magnetometer/rm3100-core.c
> 
> The rm3100 driver doesn't do any checks in the setup_ops for 'currentmode' as
> far as I could see.
> 
> So, Lars' patch could work nicely to fix this current case and not break others.
> 
> Semantically though, it would sound nicer to have a 'nextmode' parameter
> somewhere; maybe on the setup_ops(indio_dev, nextmode)?
> Though, only those 3 drivers would really ever use it; so doing it like that
> sounds like overkill.
> 
> So, we're left with Lars' patch or we could add an 'indio_dev->nextmode' field,
> that may be used in just these 3 drivers [which again: sounds overkill at this
> point in time].
> 
> Alternatively, this 'indio_dev->currentmode' could be removed from all these 3
> drivers somehow. But that needs testing and a thorough understanding of all 3
> drivers and what they're doing, to do properly.
> -------------------------------------------------------------------

Hi Alex,

Thanks for finding this. I will test this with the at91-sama5d2_adc 
driver on Jonathan's testing branch. I will let you know of the results.

Eugen

> 
>   drivers/iio/industrialio-buffer.c | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 30af8af8f312..efcc44b62946 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -989,6 +989,7 @@ static int iio_enable_buffers(struct iio_dev *indio_dev,
>          indio_dev->active_scan_mask = config->scan_mask;
>          indio_dev->scan_timestamp = config->scan_timestamp;
>          indio_dev->scan_bytes = config->scan_bytes;
> +       indio_dev->currentmode = config->mode;
> 
>          iio_update_demux(indio_dev);
> 
> @@ -1024,8 +1025,6 @@ static int iio_enable_buffers(struct iio_dev *indio_dev,
>                          goto err_disable_buffers;
>          }
> 
> -       indio_dev->currentmode = config->mode;
> -
>          if (indio_dev->setup_ops->postenable) {
>                  ret = indio_dev->setup_ops->postenable(indio_dev);
>                  if (ret) {
> @@ -1042,10 +1041,10 @@ static int iio_enable_buffers(struct iio_dev *indio_dev,
>                                               buffer_list)
>                  iio_buffer_disable(buffer, indio_dev);
>   err_run_postdisable:
> -       indio_dev->currentmode = INDIO_DIRECT_MODE;
>          if (indio_dev->setup_ops->postdisable)
>                  indio_dev->setup_ops->postdisable(indio_dev);
>   err_undo_config:
> +       indio_dev->currentmode = INDIO_DIRECT_MODE;
>          indio_dev->active_scan_mask = NULL;
> 
>          return ret;
> @@ -1080,8 +1079,6 @@ static int iio_disable_buffers(struct iio_dev *indio_dev)
>                          ret = ret2;
>          }
> 
> -       indio_dev->currentmode = INDIO_DIRECT_MODE;
> -
>          if (indio_dev->setup_ops->postdisable) {
>                  ret2 = indio_dev->setup_ops->postdisable(indio_dev);
>                  if (ret2 && !ret)
> @@ -1090,6 +1087,7 @@ static int iio_disable_buffers(struct iio_dev *indio_dev)
> 
>          iio_free_scan_mask(indio_dev, indio_dev->active_scan_mask);
>          indio_dev->active_scan_mask = NULL;
> +       indio_dev->currentmode = INDIO_DIRECT_MODE;
> 
>          return ret;
>   }
> --
> 2.17.1
> 

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