Date:   Sun, 14 May 2017 17:02:32 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>, mwelling@...e.org,
        Fabrice Gasnier <fabrice.gasnier@...com>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH 2/2] iio: make stm32 trigger driver use
 INDIO_HARDWARE_TRIGGERED mode

On 09/05/17 08:46, Benjamin Gaignard wrote:
> 2017-05-08 17:17 GMT+02:00 William Breathitt Gray <vilhelm.gray@...il.com>:
>> On Sun, May 07, 2017 at 02:49:16PM +0100, Jonathan Cameron wrote:
>>> On 01/05/17 01:50, Jonathan Cameron wrote:
>>>> On 27/04/17 14:29, Benjamin Gaignard wrote:
>>>>> Add validate function to be use to use the correct trigger.
>>>>> Add an attribute to configure device mode like for quadrature and
>>>>> enable modes
>>>>>
>>>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
>>>> Hmm.  I think I quite like this as an approach but have changed my
>>>> mind several times over the last few days :)
>>>>
>>>> Hence I'd ideally like some more opinions and will be leaving it
>>>> on the list for at least a short time longer.
>>>>
>>>> It's missed the current merge window anyway so plenty of time to
>>>> tick off this last element of your support.
>>>>
>>>> I also just checked and our docs for the existing modes is rubbish
>>>> (or I can't find it with a quick grep ;)
>>>> so we should tidy that up and add some description of this as well.
>>> Still looking for more input on this!
>>>
>>> Lars - do you have time for a quick look?
>>>
>>> No real rush though as we are early in the cycle.
>>>
>>> Thanks,
>>>
>>> Jonathan
>>
>> I haven't used triggers before in my drivers so perhaps I can provide
>> the naive perspective of someone approaching the API for the first time.
>>
>>  From what I gather, the INDIO_BUFFERED_TRIGGERED option is used for
>> triggers associated with a buffer; for example, a device keeping track
>> of ambient temperature may periodically sample its sensors and store the
>> data in a buffer for later evaluation.
>>
>> The INDIO_EVENT_TRIGGERED option appears to be used for triggers
>> associated with some sort of event; for example, a threshold voltage is
>> reached on an ADC device.
>>
>> I'm having trouble groking how the INDIO_HARDWARE_TRIGGERED option
>> differs from the INDIO_EVENT_TRIGGERED option. It looks like the
>> INDIO_HARDWARE_TRIGGERED option is used in this case to associate a
>> trigger with a clock edge (first timer chained to second timer).
>> Wouldn't an INDIO_EVENT_TRIGGERED option be sufficient in this case
>> where the event is defined as the clock edge input to the second timer?
> 
> The main difference I have introduce between INDIO_EVENT_TRIGGERED and
> INDIO_HARDWARE_TRIGGERED is that this last one doesn't have poll function
> (i.e. userland can't wait on the event).
INDIO_EVENT_TRIGGERED has a different intent as well. It's about doing
synchronized acquisition of whether a threshold has been passed or not.
It's used for comparator chips that don't have anything else to them.
Right now the only user is the hi8435.  It took a lot of bouncing backwards
and forwards before we came up with this way of handling that chip.
So what you have is a comparator with lots of channels, but it will only
give you info on which are above threshold when you ask it (not interrupts
or internal clocking).  Odd beasts typically used in PLCs where you have
a scan function polling the lot in realtime very 5 msecs or so.

> For me userland doesn't need to be informed of each clock rising edge.
> More generally this new mode can be used when the event can't/doesn't need be
> notified to userland which is the case in my hardware where it is a
> signal on internal
> wire.
Absolutely.  The 'fun' corner case is triggers that 'can' be exposed to userspace
(so there is an interrupt available) but don't have to be to run the
capture on a tightly coupled bit of hardware.  Conceptually there is a hardware
implementation of the interrupt handler available.
> 
>>
>> William Breathitt Gray
>>
>>>>
>>>> Jonathan
>>>>> ---
>>>>>   .../ABI/testing/sysfs-bus-iio-timer-stm32          | 15 ++++++
>>>>>   drivers/iio/trigger/stm32-timer-trigger.c          | 61 ++++++++++++++++++++++
>>>>>   2 files changed, 76 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-timer-stm32 b/Documentation/ABI/testing/sysfs-bus-iio-timer-stm32
>>>>> index 230020e..cccdf57 100644
>>>>> --- a/Documentation/ABI/testing/sysfs-bus-iio-timer-stm32
>>>>> +++ b/Documentation/ABI/testing/sysfs-bus-iio-timer-stm32
>>>>> @@ -90,3 +90,18 @@ Description:
>>>>>                      Counting is enabled on rising edge of the connected
>>>>>                      trigger, and remains enabled for the duration of this
>>>>>                      selected mode.
>>>>> +
>>>>> +What:              /sys/bus/iio/devices/iio:deviceX/in_count_trigger_mode_available
>>>>> +KernelVersion:     4.13
>>>>> +Contact:   benjamin.gaignard@...com
>>>>> +Description:
>>>>> +           Reading returns the list possible trigger modes.
>>>>> +
>>>>> +What:              /sys/bus/iio/devices/iio:deviceX/in_count0_trigger_mode
>>>>> +KernelVersion:     4.13
>>>>> +Contact:   benjamin.gaignard@...com
>>>>> +Description:
>>>>> +           Configure the device counter trigger mode
>>>>> +           counting direction is set by in_count0_count_direction
>>>>> +           attribute and the counter is clocked by the connected trigger
>>>>> +           rising edges.
>>>>> diff --git a/drivers/iio/trigger/stm32-timer-trigger.c b/drivers/iio/trigger/stm32-timer-trigger.c
>>>>> index 0f1a2cf..7c6e90e 100644
>>>>> --- a/drivers/iio/trigger/stm32-timer-trigger.c
>>>>> +++ b/drivers/iio/trigger/stm32-timer-trigger.c
>>>>> @@ -347,12 +347,70 @@ static int stm32_counter_write_raw(struct iio_dev *indio_dev,
>>>>>      return -EINVAL;
>>>>>   }
>>>>>
>>>>> +static int stm32_counter_validate_trigger(struct iio_dev *indio_dev,
>>>>> +                                     struct iio_trigger *trig)
>>>>> +{
>>>>> +   struct stm32_timer_trigger *priv = iio_priv(indio_dev);
>>>>> +   const char * const *cur = priv->valids;
>>>>> +   unsigned int i = 0;
>>>>> +
>>>>> +   if (!is_stm32_timer_trigger(trig))
>>>>> +           return -EINVAL;
>>>>> +
>>>>> +   while (cur && *cur) {
>>>>> +           if (!strncmp(trig->name, *cur, strlen(trig->name))) {
>>>>> +                   regmap_update_bits(priv->regmap,
>>>>> +                                      TIM_SMCR, TIM_SMCR_TS,
>>>>> +                                      i << TIM_SMCR_TS_SHIFT);
>>>>> +                   return 0;
>>>>> +           }
>>>>> +           cur++;
>>>>> +           i++;
>>>>> +   }
>>>>> +
>>>>> +   return -EINVAL;
>>>>> +}
>>>>> +
>>>>>   static const struct iio_info stm32_trigger_info = {
>>>>>      .driver_module = THIS_MODULE,
>>>>> +   .validate_trigger = stm32_counter_validate_trigger,
>>>>>      .read_raw = stm32_counter_read_raw,
>>>>>      .write_raw = stm32_counter_write_raw
>>>>>   };
>>>>>
>>>>> +static const char *const stm32_trigger_modes[] = {
>>>>> +   "trigger",
>>>>> +};
>>>>> +
>>>>> +static int stm32_set_trigger_mode(struct iio_dev *indio_dev,
>>>>> +                             const struct iio_chan_spec *chan,
>>>>> +                             unsigned int mode)
>>>>> +{
>>>>> +   struct stm32_timer_trigger *priv = iio_priv(indio_dev);
>>>>> +
>>>>> +   regmap_update_bits(priv->regmap, TIM_SMCR, TIM_SMCR_SMS, TIM_SMCR_SMS);
>>>>> +
>>>>> +   return 0;
>>>>> +}
>>>>> +
>>>>> +static int stm32_get_trigger_mode(struct iio_dev *indio_dev,
>>>>> +                             const struct iio_chan_spec *chan)
>>>>> +{
>>>>> +   struct stm32_timer_trigger *priv = iio_priv(indio_dev);
>>>>> +   u32 smcr;
>>>>> +
>>>>> +   regmap_read(priv->regmap, TIM_SMCR, &smcr);
>>>>> +
>>>>> +   return smcr == TIM_SMCR_SMS ? 0 : -EINVAL;
>>>>> +}
>>>>> +
>>>>> +static const struct iio_enum stm32_trigger_mode_enum = {
>>>>> +   .items = stm32_trigger_modes,
>>>>> +   .num_items = ARRAY_SIZE(stm32_trigger_modes),
>>>>> +   .set = stm32_set_trigger_mode,
>>>>> +   .get = stm32_get_trigger_mode
>>>>> +};
>>>>> +
>>>>>   static const char *const stm32_enable_modes[] = {
>>>>>      "always",
>>>>>      "gated",
>>>>> @@ -536,6 +594,8 @@ static ssize_t stm32_count_set_preset(struct iio_dev *indio_dev,
>>>>>      IIO_ENUM_AVAILABLE("quadrature_mode", &stm32_quadrature_mode_enum),
>>>>>      IIO_ENUM("enable_mode", IIO_SEPARATE, &stm32_enable_mode_enum),
>>>>>      IIO_ENUM_AVAILABLE("enable_mode", &stm32_enable_mode_enum),
>>>>> +   IIO_ENUM("trigger_mode", IIO_SEPARATE, &stm32_trigger_mode_enum),
>>>>> +   IIO_ENUM_AVAILABLE("trigger_mode", &stm32_trigger_mode_enum),
>>>>>      {}
>>>>>   };
>>>>>
>>>>> @@ -560,6 +620,7 @@ static struct stm32_timer_trigger *stm32_setup_counter_device(struct device *dev
>>>>>      indio_dev->name = dev_name(dev);
>>>>>      indio_dev->dev.parent = dev;
>>>>>      indio_dev->info = &stm32_trigger_info;
>>>>> +   indio_dev->modes = INDIO_HARDWARE_TRIGGERED;
>>>>>      indio_dev->num_channels = 1;
>>>>>      indio_dev->channels = &stm32_trigger_channel;
>>>>>      indio_dev->dev.of_node = dev->of_node;
>>>>>
>>>>
>>>> --
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>>>>
>>>
> 
> 
> 

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