Subject: Re: [PATCH 3/3] counter: Add atmel TCB capture counter

From: William Breathitt Gray <[email-masked]>
Date: Thu, 9 Apr 2020 09:16:37 -0400

On Thu, Apr 09, 2020 at 10:25:31AM +0200, Kamel Bouhara wrote:
> On Wed, Apr 08, 2020 at 05:31:03PM -0400, William Breathitt Gray wrote:
> > On Mon, Apr 06, 2020 at 05:53:20PM +0200, Kamel Bouhara wrote:
> > > This drivers allows to use the capture mode of the Timer Counter Block
> > > hardware block available in Atmel SoCs through the counter subsystem.
> > >
> > > Two functions of the counter are supported for the moment: period
> > > capture and quadrature decoder. The latter is only supported by the
> > > SAMA5 series of SoCs.
> > >
> > > For the period capture mode a basic setup has been chosen that will
> > > reset the counter each time the period is actually reached. Of course
> > > the device offers much more possibilities.
> > >
> > > For quadrature mode, both channel 0 and 1 must be configured even if we
> > > only capture the position (no revolution/rotation).
> > >
> > > Signed-off-by: Kamel Bouhara <[email-masked]>
> >
> > Hi Kamel,
> >
> 
> Hi William,
> 
> > Thank you for submitting support for this driver. Since this is a new
> > counter driver, make sure to create an entry for it in the top-level
> > MAINTAINERS file so users know who to contact to report bugs and other
> > issues.
> >
> 
> I'll skip this if you're ok with the fact that the file name already
> match the at91 maintainers ?

No problem, you can skip this, I didn't realize it was already matching.

William Breathitt Gray

> 
> > I've written some more comments inline below.
> >
> > > ---
> > >  drivers/counter/Kconfig             |  11 +
> > >  drivers/counter/Makefile            |   1 +
> > >  drivers/counter/atmel-tcb-capture.c | 388 ++++++++++++++++++++++++++++
> > >  3 files changed, 400 insertions(+)
> > >  create mode 100644 drivers/counter/atmel-tcb-capture.c
> > >
> > > diff --git a/drivers/counter/Kconfig b/drivers/counter/Kconfig
> > > index c80fa76bb531..c50d7453ec33 100644
> > > --- a/drivers/counter/Kconfig
> > > +++ b/drivers/counter/Kconfig
> > > @@ -70,4 +70,15 @@ config FTM_QUADDEC
> > >  	  To compile this driver as a module, choose M here: the
> > >  	  module will be called ftm-quaddec.
> > >
> > > +config ATMEL_TCB_CAPTURE
> > > +	tristate "Atmel Timer Counter Capture driver"
> > > +	depends on HAS_IOMEM && OF
> > > +	select REGMAP_MMIO
> > > +	help
> > > +	  Select this option to enable the Atmel Timer Counter Block
> > > +	  capture driver.
> > > +
> > > +	  To compile this driver as a module, choose M here: the
> > > +	  module will be called atmel-tcb-capture.
> > > +
> > >  endif # COUNTER
> > > diff --git a/drivers/counter/Makefile b/drivers/counter/Makefile
> > > index 55142d1f4c43..70c5b8924588 100644
> > > --- a/drivers/counter/Makefile
> > > +++ b/drivers/counter/Makefile
> > > @@ -10,3 +10,4 @@ obj-$(CONFIG_STM32_TIMER_CNT)	+= stm32-timer-cnt.o
> > >  obj-$(CONFIG_STM32_LPTIMER_CNT)	+= stm32-lptimer-cnt.o
> > >  obj-$(CONFIG_TI_EQEP)		+= ti-eqep.o
> > >  obj-$(CONFIG_FTM_QUADDEC)	+= ftm-quaddec.o
> > > +obj-$(CONFIG_ATMEL_TCB_CAPTURE)	+= atmel-tcb-capture.o
> > > diff --git a/drivers/counter/atmel-tcb-capture.c b/drivers/counter/atmel-tcb-capture.c
> > > new file mode 100644
> > > index 000000000000..6ac809503f90
> > > --- /dev/null
> > > +++ b/drivers/counter/atmel-tcb-capture.c
> > > @@ -0,0 +1,388 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/**
> > > + * Copyright (C) 2020 Atmel
> > > + *
> > > + * Author: Kamel Bouhara <[email-masked]>
> > > + *
> > > + */
> > > +#include <linux/clk.h>
> > > +#include <linux/counter.h>
> > > +#include <linux/mfd/syscon.h>
> > > +#include <linux/module.h>
> > > +#include <linux/mutex.h>
> > > +#include <linux/of.h>
> > > +#include <linux/of_device.h>
> > > +#include <linux/platform_device.h>
> > > +#include <linux/regmap.h>
> > > +#include <soc/at91/atmel_tcb.h>
> > > +
> > > +#define ATMEL_TC_CMR_MASK	(ATMEL_TC_LDRA_RISING | ATMEL_TC_LDRB_FALLING | \
> > > +				 ATMEL_TC_ETRGEDG_RISING | ATMEL_TC_LDBDIS | \
> > > +				 ATMEL_TC_LDBSTOP)
> > > +
> > > +#define ATMEL_TC_QDEN			BIT(8)
> > > +#define ATMEL_TC_POSEN			BIT(9)
> > > +
> > > +struct atmel_tc_data {
> > > +	const struct atmel_tcb_config *tc_cfg;
> > > +	struct counter_device counter;
> > > +	struct regmap *regmap;
> > > +	int qdec_mode;
> > > +	int num_channels;
> > > +	int channel[2];
> > > +	bool trig_inverted;
> > > +};
> > > +
> > > +enum atmel_tc_count_function {
> > > +	ATMEL_TC_FUNCTION_INCREASE,
> > > +	ATMEL_TC_FUNCTION_QUADRATURE,
> > > +};
> > > +
> > > +static enum counter_count_function atmel_tc_count_functions[] = {
> > > +	[ATMEL_TC_FUNCTION_INCREASE] = COUNTER_COUNT_FUNCTION_INCREASE,
> > > +	[ATMEL_TC_FUNCTION_QUADRATURE] = COUNTER_COUNT_FUNCTION_QUADRATURE_X4,
> > > +};
> > > +
> > > +enum atmel_tc_synapse_action {
> > > +	ATMEL_TC_SYNAPSE_ACTION_NONE = 0,
> > > +	ATMEL_TC_SYNAPSE_ACTION_RISING_EDGE,
> > > +	ATMEL_TC_SYNAPSE_ACTION_FALLING_EDGE,
> > > +	ATMEL_TC_SYNAPSE_ACTION_BOTH_EDGE
> > > +};
> > > +
> > > +static enum counter_synapse_action atmel_tc_synapse_actions[] = {
> > > +	[ATMEL_TC_SYNAPSE_ACTION_NONE] = COUNTER_SYNAPSE_ACTION_NONE,
> > > +	[ATMEL_TC_SYNAPSE_ACTION_RISING_EDGE] = COUNTER_SYNAPSE_ACTION_RISING_EDGE,
> > > +	[ATMEL_TC_SYNAPSE_ACTION_FALLING_EDGE] = COUNTER_SYNAPSE_ACTION_FALLING_EDGE,
> > > +	[ATMEL_TC_SYNAPSE_ACTION_BOTH_EDGE] = COUNTER_SYNAPSE_ACTION_BOTH_EDGES,
> > > +};
> > > +
> > > +static struct counter_signal atmel_tc_count_signals[] = {
> > > +	{
> > > +		.id = 0,
> > > +		.name = "Channel A",
> > > +	},
> > > +	{
> > > +		.id = 1,
> > > +		.name = "Channel B",
> > > +	}
> > > +};
> > > +
> > > +static struct counter_synapse atmel_tc_count_synapses[] = {
> > > +	{
> > > +		.actions_list = atmel_tc_synapse_actions,
> > > +		.num_actions = ARRAY_SIZE(atmel_tc_synapse_actions),
> > > +		.signal = &atmel_tc_count_signals[0]
> > > +	},
> > > +	{
> > > +		.actions_list = atmel_tc_synapse_actions,
> > > +		.num_actions = ARRAY_SIZE(atmel_tc_synapse_actions),
> > > +		.signal = &atmel_tc_count_signals[1]
> > > +	}
> > > +};
> > > +
> > > +static int atmel_tc_count_function_get(struct counter_device *counter,
> > > +				       struct counter_count *count,
> > > +				       size_t *function)
> > > +{
> > > +	struct atmel_tc_data *const priv = counter->priv;
> > > +
> > > +	if (priv->qdec_mode)
> > > +		*function = ATMEL_TC_FUNCTION_QUADRATURE;
> > > +	else
> > > +		*function = ATMEL_TC_FUNCTION_INCREASE;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int atmel_tc_count_function_set(struct counter_device *counter,
> > > +				       struct counter_count *count,
> > > +				       size_t function)
> > > +{
> > > +	struct atmel_tc_data *const priv = counter->priv;
> > > +	u32 bmr, cmr;
> > > +
> > > +	regmap_read(priv->regmap, ATMEL_TC_BMR, &bmr);
> > > +	regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], CMR), &cmr);
> > > +
> > > +	/* Set capture mode */
> > > +	cmr &= ~ATMEL_TC_WAVE;
> > > +
> > > +	switch (function) {
> > > +	case ATMEL_TC_FUNCTION_INCREASE:
> > > +		priv->qdec_mode = 0;
> > > +		/* Set highest rate based on whether soc has gclk or not */
> > > +		bmr &= ~(ATMEL_TC_QDEN | ATMEL_TC_POSEN);
> > > +		if (priv->tc_cfg->has_gclk)
> > > +			cmr |= ATMEL_TC_TIMER_CLOCK2;
> > > +		else
> > > +			cmr |= ATMEL_TC_TIMER_CLOCK1;
> > > +		/* Setup the period capture mode */
> > > +		cmr |=  ATMEL_TC_CMR_MASK;
> > > +		cmr &= ~(ATMEL_TC_ABETRG | ATMEL_TC_XC0);
> > > +		break;
> > > +	case ATMEL_TC_FUNCTION_QUADRATURE:
> > > +		if (!priv->tc_cfg->has_qdec)
> > > +			return -ENODEV;
> >
> > I think returning an -EINVAL here might be better. I can understand that
> > the system does not have a quadrature encoder device in this case, but
> > from the user perspective they are requesting to set the function for
> > the existing counter device. Therefore, if the existing counter device
> > does not support the requested function, it makes sense to report the
> > issue as simply an invalid argument (return -EINVAL) for this particular
> > device.
> >
> 
> Good point, fixed for v2.
> 
> > > +		/* In QDEC mode settings both channels 0 and 1 are required */
> > > +		if (priv->num_channels < 2 || priv->channel[0] != 0 ||
> > > +		    priv->channel[1] != 1) {
> > > +			pr_err("Invalid channels number or id for quadrature mode\n");
> > > +			return -EINVAL;
> > > +		}
> > > +		priv->qdec_mode = 1;
> > > +		bmr |= ATMEL_TC_QDEN | ATMEL_TC_POSEN;
> > > +		cmr |= ATMEL_TC_ETRGEDG_RISING | ATMEL_TC_ABETRG | ATMEL_TC_XC0;
> > > +		break;
> > > +	}
> > > +
> > > +	regmap_write(priv->regmap, ATMEL_TC_BMR, bmr);
> > > +	regmap_write(priv->regmap, ATMEL_TC_REG(priv->channel[0], CMR), cmr);
> > > +
> > > +	/* Enable clock and trigger counter */
> > > +	regmap_write(priv->regmap, ATMEL_TC_REG(priv->channel[0], CCR),
> > > +		     ATMEL_TC_CLKEN | ATMEL_TC_SWTRG);
> > > +
> > > +	if (priv->qdec_mode) {
> > > +		regmap_write(priv->regmap,
> > > +			     ATMEL_TC_REG(priv->channel[1], CMR), cmr);
> > > +		regmap_write(priv->regmap,
> > > +			     ATMEL_TC_REG(priv->channel[1], CCR),
> > > +			     ATMEL_TC_CLKEN | ATMEL_TC_SWTRG);
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int atmel_tc_count_signal_read(struct counter_device *counter,
> > > +				      struct counter_signal *signal,
> > > +				      enum counter_signal_value *val)
> > > +{
> > > +	struct atmel_tc_data *const priv = counter->priv;
> > > +	bool sigstatus;
> > > +	u32 sr;
> > > +
> > > +	regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], SR), &sr);
> > > +
> > > +	if (priv->trig_inverted)
> > > +		sigstatus = (sr & ATMEL_TC_MTIOB);
> > > +	else
> > > +		sigstatus = (sr & ATMEL_TC_MTIOA);
> > > +
> > > +	*val = sigstatus ? COUNTER_SIGNAL_HIGH : COUNTER_SIGNAL_LOW;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int atmel_tc_count_action_get(struct counter_device *counter,
> > > +				     struct counter_count *count,
> > > +				     struct counter_synapse *synapse,
> > > +				     size_t *action)
> > > +{
> > > +	struct atmel_tc_data *const priv = counter->priv;
> > > +	u32 cmr;
> > > +
> > > +	regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], CMR), &cmr);
> > > +
> > > +	*action = ATMEL_TC_SYNAPSE_ACTION_NONE;
> > > +
> > > +	if (cmr & ATMEL_TC_ETRGEDG_NONE)
> > > +		*action = ATMEL_TC_SYNAPSE_ACTION_NONE;
> > > +	else if (cmr & ATMEL_TC_ETRGEDG_RISING)
> > > +		*action = ATMEL_TC_SYNAPSE_ACTION_RISING_EDGE;
> > > +	else if (cmr & ATMEL_TC_ETRGEDG_FALLING)
> > > +		*action = ATMEL_TC_SYNAPSE_ACTION_FALLING_EDGE;
> > > +	else if (cmr & ATMEL_TC_ETRGEDG_BOTH)
> > > +		*action = ATMEL_TC_SYNAPSE_ACTION_BOTH_EDGE;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int atmel_tc_count_action_set(struct counter_device *counter,
> > > +				     struct counter_count *count,
> > > +				     struct counter_synapse *synapse,
> > > +				     size_t action)
> > > +{
> > > +	struct atmel_tc_data *const priv = counter->priv;
> > > +	u32 edge = ATMEL_TC_ETRGEDG_NONE;
> > > +
> > > +	switch (action) {
> > > +	case ATMEL_TC_SYNAPSE_ACTION_NONE:
> > > +		edge = ATMEL_TC_ETRGEDG_NONE;
> > > +		break;
> > > +	case ATMEL_TC_SYNAPSE_ACTION_RISING_EDGE:
> > > +		edge = ATMEL_TC_ETRGEDG_RISING;
> > > +		break;
> > > +	case ATMEL_TC_SYNAPSE_ACTION_FALLING_EDGE:
> > > +		edge = ATMEL_TC_ETRGEDG_FALLING;
> > > +		break;
> > > +	case ATMEL_TC_SYNAPSE_ACTION_BOTH_EDGE:
> > > +		edge = ATMEL_TC_ETRGEDG_BOTH;
> > > +		break;
> > > +	}
> > > +
> > > +	return regmap_write_bits(priv->regmap,
> > > +				ATMEL_TC_REG(priv->channel[0], CMR),
> > > +				ATMEL_TC_ETRGEDG, edge);
> >
> > Are users able to adjust the edges like this even if the device is
> > configured for QDEC mode? If not, you should return -EINVAL if the
> > device is in QDEC mode.
> >
> 
> You're right, in QDEC mode, rising edge must be selected as the external
> trigger edge.
> 
> Fixed.
> 
> > > +}
> > > +
> > > +static int atmel_tc_count_read(struct counter_device *counter,
> > > +			       struct counter_count *count,
> > > +			       unsigned long *val)
> > > +{
> > > +	struct atmel_tc_data *const priv = counter->priv;
> > > +	u32 cnt;
> > > +
> > > +	regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], CV), &cnt);
> > > +	*val = cnt;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static struct counter_count atmel_tc_count = {
> > > +	.id = 0,
> > > +	.name = "Timer Counter",
> > > +	.functions_list = atmel_tc_count_functions,
> > > +	.num_functions = ARRAY_SIZE(atmel_tc_count_functions),
> > > +	.synapses = atmel_tc_count_synapses,
> > > +	.num_synapses = ARRAY_SIZE(atmel_tc_count_synapses),
> > > +};
> > > +
> > > +static struct counter_ops atmel_tc_ops = {
> > > +	.signal_read  = atmel_tc_count_signal_read,
> > > +	.count_read   = atmel_tc_count_read,
> > > +	.count_write  = NULL,
> >
> > No need to explicitly set count_write to NULL since it will be NULL by
> > default in this static structure.
> >
> 
> Fixed, thanks.
> 
> > > +	.function_get = atmel_tc_count_function_get,
> > > +	.function_set = atmel_tc_count_function_set,
> > > +	.action_get   = atmel_tc_count_action_get,
> > > +	.action_set   = atmel_tc_count_action_set
> > > +};
> > > +
> > > +static const struct atmel_tcb_config tcb_rm9200_config = {
> > > +		.counter_width = 16,
> > > +};
> > > +
> > > +static const struct atmel_tcb_config tcb_sam9x5_config = {
> > > +		.counter_width = 32,
> > > +};
> > > +
> > > +static const struct atmel_tcb_config tcb_sama5d2_config = {
> > > +		.counter_width = 32,
> > > +		.has_gclk = true,
> > > +		.has_qdec = true,
> > > +};
> > > +
> > > +static const struct atmel_tcb_config tcb_sama5d3_config = {
> > > +		.counter_width = 32,
> > > +		.has_qdec = true,
> > > +};
> > > +
> > > +static const struct of_device_id atmel_tc_of_match[] = {
> > > +	{ .compatible = "atmel,at91rm9200-tcb", .data = &tcb_rm9200_config, },
> > > +	{ .compatible = "atmel,at91sam9x5-tcb", .data = &tcb_sam9x5_config, },
> > > +	{ .compatible = "atmel,sama5d2-tcb", .data = &tcb_sama5d2_config, },
> > > +	{ .compatible = "atmel,sama5d3-tcb", .data = &tcb_sama5d3_config, },
> > > +	{ /* sentinel */ }
> > > +};
> > > +
> > > +static int atmel_tc_probe(struct platform_device *pdev)
> > > +{
> > > +	struct device_node *np = pdev->dev.of_node;
> > > +	const struct atmel_tcb_config *tcb_config;
> > > +	const struct of_device_id *match;
> > > +	struct atmel_tc_data *priv;
> > > +	char clk_name[] = "t0_clk";
> > > +	struct regmap *regmap;
> > > +	struct clk *clk[3];
> > > +	int channel;
> > > +	int ret, i;
> > > +
> > > +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> > > +	if (!priv)
> > > +		return -ENOMEM;
> > > +
> > > +	platform_set_drvdata(pdev, priv);
> > > +
> > > +	match = of_match_node(atmel_tc_of_match, np->parent);
> > > +	tcb_config = match->data;
> > > +	if (!tcb_config) {
> > > +		dev_err(&pdev->dev, "No matching parent node found\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	regmap = syscon_node_to_regmap(np->parent);
> > > +	if (IS_ERR(priv->regmap))
> > > +		return PTR_ERR(priv->regmap);
> > > +
> > > +	/* max. channels number is 2 when in QDEC mode */
> > > +	priv->num_channels = of_property_count_u32_elems(np, "reg");
> > > +	if (priv->num_channels < 0) {
> > > +		dev_err(&pdev->dev, "Invalid or missing channel\n");
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	/* Register channels and initialize clocks */
> > > +	for (i = 0; i < priv->num_channels; i++) {
> > > +		ret = of_property_read_u32_index(np, "reg", i, &channel);
> > > +		if (ret < 0 || channel > 2)
> > > +			return -ENODEV;
> > > +
> > > +		priv->channel[i] = channel;
> > > +
> > > +		clk_name[1] += channel;
> >
> > You're being clever here (not a bad thing) but this looks too easy to
> > get wrong and confused. I'd much rather see a snprintf here for clarity
> > and know that nothing funny is going to happen.
> >
> 
> Well ok let's be less clever for the sake of clarity :).
> 
> > > +		clk[i] = of_clk_get_by_name(np->parent, clk_name);
> > > +		if (IS_ERR(clk[i])) {
> > > +			/* Fallback to t0_clk */
> > > +			clk[i] = of_clk_get_by_name(np->parent, "t0_clk");
> > > +			if (IS_ERR(clk[i]))
> > > +				return PTR_ERR(clk[i]);
> > > +		}
> > > +
> > > +		ret = clk_prepare_enable(clk[i]);
> > > +		if (ret)
> > > +			return ret;
> > > +
> > > +		dev_info(&pdev->dev,
> > > +			 "Initialized capture mode on channel %d\n",
> > > +			 channel);
> > > +	}
> > > +
> > > +	priv->tc_cfg = tcb_config;
> > > +	priv->regmap = regmap;
> > > +	priv->counter.name = dev_name(&pdev->dev);
> > > +	priv->counter.parent = &pdev->dev;
> > > +	priv->counter.ops = &atmel_tc_ops;
> > > +	priv->counter.num_counts = 1;
> >
> > Use ARRAY_SIZE here so that future reviewers will know that num_counts
> > matches what's in the atmel_tc_count array without having to check so
> > themselves.
> >
> 
> OK, yet the atmel_tc_count isn't an array I guess that it shall be.
> 
> Thanks,
> 
> Kamel
> 
> > William Breathitt Gray
> >
> > > +	priv->counter.counts = &atmel_tc_count;
> > > +	priv->counter.num_signals = ARRAY_SIZE(atmel_tc_count_signals);
> > > +	priv->counter.signals = atmel_tc_count_signals;
> > > +	priv->counter.priv = priv;
> > > +
> > > +	ret = devm_counter_register(&pdev->dev, &priv->counter);
> > > +	if (ret < 0) {
> > > +		for (i = 0; i < priv->num_channels; i++)
> > > +			clk_disable_unprepare(clk[i]);
> > > +		return ret;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static const struct of_device_id atmel_tc_dt_ids[] = {
> > > +	{ .compatible = "atmel,tcb-capture", },
> > > +	{ /* sentinel */ },
> > > +};
> > > +MODULE_DEVICE_TABLE(of, atmel_tc_dt_ids);
> > > +
> > > +static struct platform_driver atmel_tc_driver = {
> > > +	.probe = atmel_tc_probe,
> > > +	.driver = {
> > > +		.name = "atmel-tcb-capture",
> > > +		.of_match_table = atmel_tc_dt_ids,
> > > +	},
> > > +};
> > > +module_platform_driver(atmel_tc_driver);
> > > +
> > > +MODULE_AUTHOR("Kamel Bouhara <[email-masked]>");
> > > +MODULE_DESCRIPTION("Atmel TCB Capture driver");
> > > +MODULE_LICENSE("GPL v2");
> > > --
> > > 2.25.0
> > >
> 
> 
> 
> --
> Kamel Bouhara, Bootlin
> Embedded Linux and kernel engineering
> https://bootlin.com
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