Re: [PATCH v3 2/3] Input: adc-joystick - Add polled input device support

Jonathan Cameron
2022-06-19T15:23:47Z

On Sat, 18 Jun 2022 15:08:29 +0200
Artur Rojek <contact@artur-rojek.eu> wrote:

> On 2022-06-15 17:12, Chris Morgan wrote:
> > On Wed, Jun 15, 2022 at 03:43:07AM +0200, Artur Rojek wrote:
> >> On 2022-06-13 21:23, Chris Morgan wrote:
> >> > From: Chris Morgan <macromorgan@hotmail.com>
> >> >
> >> > Add polled input device support to the adc-joystick driver. This is
> >> > useful for devices which do not have hardware capable triggers on
> >> > their SARADC. Code modified from adc-joystick.c changes made by Maya
> >> > Matuszczyk.
> >> >
> >> > Signed-off-by: Maya Matuszczyk <maccraft123mc@gmail.com>
> >> > Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
> >>
> >> Hi Chris,
> >>
> >> Comments inline. I also Cc'd Paul and Jonathan, who were attached in
> >> v2.
+CC linux-iio

> >>
> >> > ---
> >> > drivers/input/joystick/adc-joystick.c | 52 +++++++++++++++++++++------
> >> > 1 file changed, 41 insertions(+), 11 deletions(-)
> >> >
> >> > diff --git a/drivers/input/joystick/adc-joystick.c
> >> > b/drivers/input/joystick/adc-joystick.c
> >> > index 78ebca7d400a..dc01cd0214d2 100644
> >> > --- a/drivers/input/joystick/adc-joystick.c
> >> > +++ b/drivers/input/joystick/adc-joystick.c
> >> > @@ -13,6 +13,10 @@
> >> >
> >> > #include <asm/unaligned.h>
> >> >
> >> > +#define ADC_JSK_POLL_INTERVAL 16
> >> > +#define ADC_JSK_POLL_MIN 8
> >> > +#define ADC_JSK_POLL_MAX 32
> >> > +
> >> > struct adc_joystick_axis {
> >> > u32 code;
> >> > s32 range[2];
> >> > @@ -26,8 +30,21 @@ struct adc_joystick {
> >> > struct adc_joystick_axis *axes;
> >> > struct iio_channel *chans;
> >> > int num_chans;
> >> > + bool polled;
> >> > };
> >> >
> >> > +static void adc_joystick_poll(struct input_dev *input)
> >> > +{
> >> > + struct adc_joystick *joy = input_get_drvdata(input);
> >> > + int i, val;
> >> > +
> >> > + for (i = 0; i < joy->num_chans; i++) {
> >> > + iio_read_channel_raw(&joy->chans[i], &val);
> >> > + input_report_abs(input, joy->axes[i].code, val);
> >> > + }
> >> > + input_sync(input);
> >> > +}
> >> > +
> >> > static int adc_joystick_handle(const void *data, void *private)
> >> > {
> >> > struct adc_joystick *joy = private;
> >> > @@ -215,8 +232,19 @@ static int adc_joystick_probe(struct
> >> > platform_device *pdev)
> >> > joy->input = input;
> >> > input->name = pdev->name;
> >> > input->id.bustype = BUS_HOST;
> >> > - input->open = adc_joystick_open;
> >> > - input->close = adc_joystick_close;
> >> > +
> >> > + if (device_property_read_bool(dev,
> >> > "adc-joystick,no-hardware-trigger"))
> >> > + joy->polled = 1;
> >> As mentioned in v2, I don't think a DT property is required here.
> >> Assuming
> >> the polled mode is a fallback for devices with no buffers, just do:
> >> ```
> >> joy->polled = !(joy->chans[0].indio_dev->modes &
> >> INDIO_ALL_BUFFER_MODES);
> >> ```
> >
> > Understood. I attempted this and noticed that it was showing I have
> > INDIO_BUFFER_TRIGGERED in addition to INDIO_DIRECT_MODE (the
> > INDIO_DIRECT_MODE is the only one specified at the hardware level
> > though). Should I just check for INDIO_BUFFER_SOFTWARE &
> > INDIO_BUFFER_HARDWARE instead? I think it's possible that the inclusion
> > of the industrialio_triggered_buffer module in my kernel is adding
> > this to the channel somehow?
> Having INDIO_BUFFER_TRIGGERED means that your saradc is capable of using
> the existing flow. You should be able to register a software trigger and
> use the adc-joystick driver without further issues.
> That said, this is where it gets problematic - there is no way to create
> an IIO trigger via Device Tree, since triggers don't describe any piece
> of hardware, and you shouldn't need to register it at runtime
> (configfs/sysfs) for communication between two kernel drivers either. At
> the same time, it's not adc-joystick's job to register an external
> trigger.
>
> Jonathan,
> I don't know what the proper approach to this should be, perhaps you
> could assist?

You are correct in your description above. Device tree folk take the view
that sysfs / hrtimer etc triggers are a policy decision so don't belong
in device tree. In general you need some userspace code to stitch up
the trigger anyway (even ADCs that provide triggers of their own often
have several).

An alternative that may make sense here would be for the adc-joystick
driver to provide a trigger of it's own. That's easy enough to do,
but as things stand we don't provide a way to control the attached
trigger from other kernel drivers (i.e. you can't do the equivalent
of writing current_trigger for another device).

It's probably not implausible to add that though. Is it worth it for
a joystick (vs doing what is done here), maybe not.

It would be worth doing if we cared about high performance (for some ADCs
anyway) but here we don't really so the polled read functions are fine.

Note many ADC drivers only support running in either polled or buffered
mode in IIO because polling random channels when doing highly optimised
accesses tends to make the drivers complex. Hence you might find this
doesn't work for all setups...

Thanks,

Jonathan

>
> Cheers,
> Artur
> >
> > Thank you.
> >
> >> > +
> >> > + if (joy->polled) {
> >> > + input_setup_polling(input, adc_joystick_poll);
> >> > + input_set_poll_interval(input, ADC_JSK_POLL_INTERVAL);
> >> > + input_set_min_poll_interval(input, ADC_JSK_POLL_MIN);
> >> > + input_set_max_poll_interval(input, ADC_JSK_POLL_MAX);
> >> > + } else {
> >> > + input->open = adc_joystick_open;
> >> > + input->close = adc_joystick_close;
> >> > + }
> >> >
> >> > error = adc_joystick_set_axes(dev, joy);
> >> > if (error)
> >> > @@ -229,16 +257,18 @@ static int adc_joystick_probe(struct
> >> > platform_device *pdev)
> >> > return error;
> >> > }
> >> >
> >> > - joy->buffer = iio_channel_get_all_cb(dev, adc_joystick_handle, joy);
> >> > - if (IS_ERR(joy->buffer)) {
> >> > - dev_err(dev, "Unable to allocate callback buffer\n");
> >> > - return PTR_ERR(joy->buffer);
> >> > - }
> >> > + if (!joy->polled) {
> >> > + joy->buffer = iio_channel_get_all_cb(dev, adc_joystick_handle, joy);
> >> Please maintain line discipline of 80 chars to stay consistent with
> >> the rest
> >> of this driver.
> >
> > Understood, sorry about that.
> >
> >> > + if (IS_ERR(joy->buffer)) {
> >> > + dev_err(dev, "Unable to allocate callback buffer\n");
> >> > + return PTR_ERR(joy->buffer);
> >> > + }
> >> >
> >> > - error = devm_add_action_or_reset(dev, adc_joystick_cleanup,
> >> > joy->buffer);
> >> > - if (error) {
> >> > - dev_err(dev, "Unable to add action\n");
> >> > - return error;
> >> > + error = devm_add_action_or_reset(dev, adc_joystick_cleanup,
> >> > joy->buffer);
> >> Same here.
> >
> > Ditto.
> >
> >>
> >> Cheers,
> >> Artur
> >> > + if (error) {
> >> > + dev_err(dev, "Unable to add action\n");
> >> > + return error;
> >> > + }
> >> > }
> >> >
> >> > return 0;