On 22/05/16 22:30, Jonathan Cameron wrote:
> On 06/03/16 20:02, Jonathan Cameron wrote:
>> This patch is in response to that of
>> Gregor Boirie <gregor.boirie@xxxxxxxxxx>
>> who proposed using a tight kthread within a device driver (be it with the
>> support factored out into a helper library) in order to basically spin as
>> fast as possible.
>>
>> It is meant as a talking point rather than a formal proposal of the code
>> (though we are heading towards that I think).
>> Also gives people some working code to mess around with.
>>
>> I proposed that this could be done with a trigger with a few constraints
>> and this is the proof (be it ugly) of that.
>>
>> There are some constraints though, some of which we would want to relax
>> if this were to move forward.
>>
>> * Will only run the thread part of the registered pollfunc. This is to
>> avoid the overhead of jumping in and out of interrupt context. Is the
>> overhead significant? Not certain but feels like it should be!
>>
>> * This limitation precludes any device that 'must' do some work in
>> interrupt context. However, that is true of few if any drivers and
>> I suspect that any that do will be restricted to using triggers they
>> provide themselves. Usually we have a top half mainly to grab a
>> timestamp as soon after the dataready type signal as possible.
>>
>> Signed-off-by: Jonathan Cameron <jic23@xxxxxxxxxx>
> Any comments on this anyone?
>
> Whilst we still haven't dealt with the question of neatly handling
> the missing top halves (where relevant) I think it might be worth taking this
> soonish as we have genuine use cases...
>
> Would be easy enough to modify the pollfunc generic timestamp code to play
> a few games to ensure it grabs a software timestamp in the threaded handler if needed
> (inserting an appropriate access function into all users)..
> say
> iio_pollfunc_get_ts_best_effort() that uses the top half stored one if available
> (also setting a 'new timestamp' available if from a hardware source) or if not
> grabs one at call time in the threaded handler.
>
>
> Jonathan
This needs a review from someone!.. Daniel, it uses your configfs stuff so could
you take a look if no one else does?
Thanks,
Jonathan
>> ---
>> drivers/iio/trigger/Kconfig | 12 +++
>> drivers/iio/trigger/Makefile | 1 +
>> drivers/iio/trigger/iio-trig-loop.c | 143 ++++++++++++++++++++++++++++++++++++
>> 3 files changed, 156 insertions(+)
>>
>> diff --git a/drivers/iio/trigger/Kconfig b/drivers/iio/trigger/Kconfig
>> index 519e6772f6f5..9feabe95eeda 100644
>> --- a/drivers/iio/trigger/Kconfig
>> +++ b/drivers/iio/trigger/Kconfig
>> @@ -24,6 +24,18 @@ config IIO_INTERRUPT_TRIGGER
>> To compile this driver as a module, choose M here: the
>> module will be called iio-trig-interrupt.
>>
>> +config IIO_TIGHTLOOP_TRIGGER
>> + tristate "A kthread based hammering loop trigger"
>> + depends on IIO_SW_TRIGGER
>> + help
>> + An experimental trigger, used to allow sensors to be sampled as fast
>> + as possible under the limitations of whatever else is going on.
>> + Uses a tight loop in a kthread. Will only work with lower half only
>> + trigger consumers.
>> +
>> + To compile this driver as a module, choose M here: the
>> + module will be called iio-trig-loop.
>> +
>> config IIO_SYSFS_TRIGGER
>> tristate "SYSFS trigger"
>> depends on SYSFS
>> diff --git a/drivers/iio/trigger/Makefile b/drivers/iio/trigger/Makefile
>> index fe06eb564367..aab4dc23303d 100644
>> --- a/drivers/iio/trigger/Makefile
>> +++ b/drivers/iio/trigger/Makefile
>> @@ -7,3 +7,4 @@
>> obj-$(CONFIG_IIO_HRTIMER_TRIGGER) += iio-trig-hrtimer.o
>> obj-$(CONFIG_IIO_INTERRUPT_TRIGGER) += iio-trig-interrupt.o
>> obj-$(CONFIG_IIO_SYSFS_TRIGGER) += iio-trig-sysfs.o
>> +obj-$(CONFIG_IIO_TIGHTLOOP_TRIGGER) += iio-trig-loop.o
>> diff --git a/drivers/iio/trigger/iio-trig-loop.c b/drivers/iio/trigger/iio-trig-loop.c
>> new file mode 100644
>> index 000000000000..dc6be28f96fe
>> --- /dev/null
>> +++ b/drivers/iio/trigger/iio-trig-loop.c
>> @@ -0,0 +1,143 @@
>> +/*
>> + * Copyright 2016 Jonathan Cameron <jic23@xxxxxxxxxx>
>> + *
>> + * Licensed under the GPL-2.
>> + *
>> + * Based on a mashup of the hrtimer trigger and continuous sampling proposal of
>> + * Gregor Boirie <gregor.boirie@xxxxxxxxxx>
>> + *
>> + * Note this is still rather experimental and may eat babies.
>> + *
>> + * Todo
>> + * * Protect against connection of devices that 'need' the top half
>> + * handler.
>> + * * Work out how to run top half handlers in this context if it is
>> + * safe to do so (timestamp grabbing for example)
>> + *
>> + * Tested against a max1363. Used about 33% cpu for the thread and 20%
>> + * for generic_buffer piping to /dev/null. Watermark set at 64 on a 128
>> + * element kfifo buffer.
>> + */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/slab.h>
>> +#include <linux/irq_work.h>
>> +#include <linux/kthread.h>
>> +#include <linux/freezer.h>
>> +
>> +#include <linux/iio/iio.h>
>> +#include <linux/iio/trigger.h>
>> +#include <linux/iio/sw_trigger.h>
>> +
>> +struct iio_loop_info {
>> + struct iio_sw_trigger swt;
>> + struct task_struct *task;
>> +};
>> +
>> +static struct config_item_type iio_loop_type = {
>> + .ct_owner = THIS_MODULE,
>> +};
>> +
>> +static int iio_loop_thread(void *data)
>> +{
>> + struct iio_trigger *trig = data;
>> +
>> + set_freezable();
>> +
>> + do {
>> + iio_trigger_poll_chained(trig);
>> + } while (likely(!kthread_freezable_should_stop(NULL)));
>> +
>> + return 0;
>> +}
>> +
>> +static int iio_loop_trigger_set_state(struct iio_trigger *trig, bool state)
>> +{
>> + struct iio_loop_info *loop_trig = iio_trigger_get_drvdata(trig);
>> +
>> + if (state) {
>> + loop_trig->task = kthread_run(iio_loop_thread,
>> + trig, trig->name);
>> + if (unlikely(IS_ERR(loop_trig->task))) {
>> + dev_err(&trig->dev,
>> + "failed to create trigger loop thread\n");
>> + return PTR_ERR(loop_trig->task);
>> + }
>> + } else {
>> + kthread_stop(loop_trig->task);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static const struct iio_trigger_ops iio_loop_trigger_ops = {
>> + .set_trigger_state = iio_loop_trigger_set_state,
>> + .owner = THIS_MODULE,
>> +};
>> +
>> +static struct iio_sw_trigger *iio_trig_loop_probe(const char *name)
>> +{
>> + struct iio_loop_info *trig_info;
>> + int ret;
>> +
>> + trig_info = kzalloc(sizeof(*trig_info), GFP_KERNEL);
>> + if (!trig_info)
>> + return ERR_PTR(-ENOMEM);
>> +
>> + trig_info->swt.trigger = iio_trigger_alloc("%s", name);
>> + if (!trig_info->swt.trigger) {
>> + ret = -ENOMEM;
>> + goto err_free_trig_info;
>> + }
>> +
>> + iio_trigger_set_drvdata(trig_info->swt.trigger, trig_info);
>> + trig_info->swt.trigger->ops = &iio_loop_trigger_ops;
>> +
>> + ret = iio_trigger_register(trig_info->swt.trigger);
>> + if (ret)
>> + goto err_free_trigger;
>> +
>> + iio_swt_group_init_type_name(&trig_info->swt, name, &iio_loop_type);
>> +
>> + return &trig_info->swt;
>> +
>> +err_free_trigger:
>> + iio_trigger_free(trig_info->swt.trigger);
>> +err_free_trig_info:
>> + kfree(trig_info);
>> +
>> + return ERR_PTR(ret);
>> +}
>> +
>> +static int iio_trig_loop_remove(struct iio_sw_trigger *swt)
>> +{
>> + struct iio_loop_info *trig_info;
>> +
>> + trig_info = iio_trigger_get_drvdata(swt->trigger);
>> +
>> + iio_trigger_unregister(swt->trigger);
>> + iio_trigger_free(swt->trigger);
>> + kfree(trig_info);
>> +
>> + return 0;
>> +}
>> +
>> +static const struct iio_sw_trigger_ops iio_trig_loop_ops = {
>> + .probe = iio_trig_loop_probe,
>> + .remove = iio_trig_loop_remove,
>> +};
>> +
>> +static struct iio_sw_trigger_type iio_trig_loop = {
>> + .name = "loop",
>> + .owner = THIS_MODULE,
>> + .ops = &iio_trig_loop_ops,
>> +};
>> +
>> +module_iio_sw_trigger_driver(iio_trig_loop);
>> +
>> +MODULE_AUTHOR("Jonathan Cameron <jic23@xxxxxxxxxx>");
>> +MODULE_DESCRIPTION("Loop based trigger for the iio subsystem");
>> +MODULE_LICENSE("GPL v2");
>> +MODULE_ALIAS("platform:iio-trig-loop");
>>
>
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