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Date:   Sat, 28 Mar 2020 17:22:56 +0000
From:   Jonathan Cameron <jic23@jic23.retrosnub.co.uk>
To:     Gwendal Grignou <gwendal@chromium.org>
Cc:     bleung@chromium.org, enric.balletbo@collabora.com,
        Jonathan.Cameron@huawei.com, linux-iio@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 12/12] iio: cros_ec: flush as hwfifo attribute
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In-Reply-To: <20200327223443.6006-13-gwendal@chromium.org>
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        <20200327223443.6006-13-gwendal@chromium.org>
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On Fri, 27 Mar 2020 15:34:43 -0700
Gwendal Grignou <gwendal@chromium.org> wrote:

> Add buffer/hwfifo_flush. It is not part of the ABI, but it follows ST
> and HID lead: Tells the sensor hub to send to the host all pending
> sensor events.
> 
> Signed-off-by: Gwendal Grignou <gwendal@chromium.org>

Unless I'm missing something there aren't any other drivers providing
an explicit flush attribute. The nearest equivalent is the flush
callback which reads out stuff that is in a fifo to be read, but which
hasn't yet reached a watermark to trigger normal readback.

Can we do something similar here?

If not this needs ABI documentation in Documentation/ABI/testing/...
I'm not keen on it in becoming general ABI unless I'm missing a
strong argument in favour of it.

Jonathan


> ---
> No changes in v7.
> New in v6.
> 
>  .../cros_ec_sensors/cros_ec_sensors_core.c    | 28 +++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> index c831915ca7e56..aaf124a82e0e4 100644
> --- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> +++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> @@ -113,6 +113,33 @@ static int cros_ec_sensor_set_ec_rate(struct cros_ec_sensors_core_state *st,
>  	return ret;
>  }
>  
> +static ssize_t cros_ec_sensors_flush(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t len)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct cros_ec_sensors_core_state *st = iio_priv(indio_dev);
> +	int ret = 0;
> +	bool flush;
> +
> +	ret = strtobool(buf, &flush);
> +	if (ret < 0)
> +		return ret;
> +	if (!flush)
> +		return -EINVAL;
> +
> +	mutex_lock(&st->cmd_lock);
> +	st->param.cmd = MOTIONSENSE_CMD_FIFO_FLUSH;
> +	ret = cros_ec_motion_send_host_cmd(st, 0);
> +	if (ret != 0)
> +		dev_warn(&indio_dev->dev, "Unable to flush sensor\n");
> +	mutex_unlock(&st->cmd_lock);
> +	return ret ? ret : len;
> +}
> +
> +static IIO_DEVICE_ATTR(hwfifo_flush, 0644, NULL,
> +		       cros_ec_sensors_flush, 0);
> +
>  static ssize_t cros_ec_sensor_set_report_latency(struct device *dev,
>  						 struct device_attribute *attr,
>  						 const char *buf, size_t len)
> @@ -175,6 +202,7 @@ static ssize_t hwfifo_watermark_max_show(struct device *dev,
>  static IIO_DEVICE_ATTR_RO(hwfifo_watermark_max, 0);
>  
>  const struct attribute *cros_ec_sensor_fifo_attributes[] = {
> +	&iio_dev_attr_hwfifo_flush.dev_attr.attr,
>  	&iio_dev_attr_hwfifo_timeout.dev_attr.attr,
>  	&iio_dev_attr_hwfifo_watermark_max.dev_attr.attr,
>  	NULL,