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SubjectRe: [PATCH] counter: 104-quad-8: Support Differential Encoder Cable Status
On Sat, 22 Feb 2020 10:43:40 -0500
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> The ACCES 104-QUAD-8 series provides status information about the
> connection state of the differential encoder cable inputs. This patch
> implements support to expose such information from these devices.
>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>

Hi William, Couple of things on the interface...

> ---
> .../ABI/testing/sysfs-bus-counter-104-quad-8 | 12 ++++++
> drivers/counter/104-quad-8.c | 38 +++++++++++++++++++
> 2 files changed, 50 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8 b/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
> index 46b1f33b2fce..492b3e98f369 100644
> --- a/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
> +++ b/Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
> @@ -1,3 +1,15 @@
> +What: /sys/bus/counter/devices/counterX/cable_status
> +KernelVersion: 5.7
> +Contact: linux-iio@vger.kernel.org
> +Description:
> + Differential encoder cable status; bits 0 through 7
> + correspond to channels 1 through 8. Writing a 0 to the
> + corresponding bit will enable the status of the
> + respective channel.
I'm never personally that keen on cases where a sysfs file doesn't have
inherent 'obviousness'. In this case we have a bitmap that doesn't make that
clear and that also that doesn't have particularly obviously meaning either
on the write or read.

Hmm. So if you wanted to keep it as a bitmap perhaps something like...

cable_test_bitmap

So a 1 (or true) would be a successful cable test on read. However that is
still not obviously something that needs an enable. It think you need to
split it.

*_enable
*_status

Next question is whether it should be a map like this? sysfs rules are usually
one value to one sysfs file. It might seem wasteful but I'd like to see something
like

cable0_test_enable
cable0_test_status
cable7_test_enable
cable7_test_status

I haven't thought about whether this could be fit better with the counter ABI
but something along those lines!

> +
> + Logic 0 = cable fault (not connected or loose wires)
> + Logic 1 = cable connection good or cable fault disabled
> +
> What: /sys/bus/counter/devices/counterX/signalY/index_polarity
> KernelVersion: 5.2
> Contact: linux-iio@vger.kernel.org
> diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> index 17e67a84777d..1cbaf7e100a3 100644
> --- a/drivers/counter/104-quad-8.c
> +++ b/drivers/counter/104-quad-8.c
> @@ -56,6 +56,7 @@ struct quad8_iio {
>
> #define QUAD8_REG_CHAN_OP 0x11
> #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16
> +#define QUAD8_DIFF_ENCODER_CABLE_STATUS 0x17
> /* Borrow Toggle flip-flop */
> #define QUAD8_FLAG_BT BIT(0)
> /* Carry Toggle flip-flop */
> @@ -1268,6 +1269,42 @@ static struct counter_count quad8_counts[] = {
> QUAD8_COUNT(7, "Channel 8 Count")
> };
>
> +static ssize_t quad8_cable_status_read(struct counter_device *counter,
> + void *private, char *buf)
> +{
> + const struct quad8_iio *const priv = counter->priv;
> + unsigned int status;
> +
> + status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
> +
> + return sprintf(buf, "0x%X\n", status);
> +}
> +
> +static ssize_t quad8_cable_status_write(struct counter_device *counter,
> + void *private, const char *buf,
> + size_t len)
> +{
> + struct quad8_iio *const priv = counter->priv;
> + u8 enable;
> + int ret;
> +
> + ret = kstrtou8(buf, 0, &enable);
> + if (ret)
> + return ret;
> +
> + outb(enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
> +
> + return len;
> +}
> +
> +static const struct counter_device_ext quad8_device_ext[] = {
> + {
> + .name = "cable_status",
> + .read = quad8_cable_status_read,
> + .write = quad8_cable_status_write
> + }
> +};
> +
> static int quad8_probe(struct device *dev, unsigned int id)
> {
> struct iio_dev *indio_dev;
> @@ -1304,6 +1341,7 @@ static int quad8_probe(struct device *dev, unsigned int id)
> quad8iio->counter.num_counts = ARRAY_SIZE(quad8_counts);
> quad8iio->counter.signals = quad8_signals;
> quad8iio->counter.num_signals = ARRAY_SIZE(quad8_signals);
> + quad8iio->counter.ext = quad8_device_ext;
> quad8iio->counter.priv = quad8iio;
> quad8iio->base = base[id];
>

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