Re: [PATCH 2/2 v4] pwm: Add driver for AXI PWM generator

[Uwe Kleine-König]

Hello,

On Fri, Mar 01, 2024 at 12:33:42PM -0500, Trevor Gamblin wrote:
> From: Drew Fustini <dfustini@xxxxxxxxxxxx>
> 
> Add support for the Analog Devices AXI PWM Generator. This device is an
> FPGA-implemented peripheral used as PWM signal generator and can be
> interfaced with AXI4. The register map of this peripheral makes it
> possible to configure the period and duty cycle of the output signal.
> 
> Link: https://wiki.analog.com/resources/fpga/docs/axi_pwm_gen
> Co-developed-by: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx>
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx>
> Co-developed-by: David Lechner <dlechner@xxxxxxxxxxxx>
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
> Signed-off-by: Drew Fustini <dfustini@xxxxxxxxxxxx>
> Acked-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
> Co-developed-by: Trevor Gamblin <tgamblin@xxxxxxxxxxxx>
> Signed-off-by: Trevor Gamblin <tgamblin@xxxxxxxxxxxx>
> ---
> v4 changes: 
> * Address feedback for driver in v3:
>   * Update to use devm_pwmchip_alloc() function
>   * Simplify use of dev symbol in axi_pwmgen_probe
>   * Remove unnecessary axi_pwmgen_from_chip function and use
>     pwmchip_get_drvdata directly
> 
> v3 changes:
> * Address feedback for driver in v2:
>   * Remove unnecessary blank line in axi_pwmgen_apply
>   * Use macros already defined in <linux/fpga/adi-axi-common.h> for
>     version checking
> 
> v2 changes:
> * Address feedback for driver and device tree in v1:
>   * Use more reasonable Kconfig approach
>   * Use common prefixes for all functions
>   * Rename axi_pwmgen struct to axi_pwmgen_ddata
>   * Change use of "pwm" to "ddata"
>   * Set and check state->polarity
>   * Multiply safely with mul_u64_u64_div_u64()
>   * Improve handling of max and zero periods
>   * Error if clk_rate_hz > NSEC_PER_SEC
>   * Add "Limitations" section at top of pwm-axi-pwmgen.c
>   * Don't disable outputs by default
>   * Remove unnecessary macros for period, duty, offset
>   * Fix axi_pwmgen_ddata alignment
>   * Don't artificially limit npwm to four
>   * Use clk_rate_exclusive_get(), balance with clk_rate_exclusive_put()
>   * Cache clk rate in axi_pwmgen_ddata
>   * Don't assign pwm->chip.base, do assign pwm->chip.atomic
> * Remove redundant calls to clk_get_rate
> * Test contents of AXI_PWMGEN_REG_CORE_MAGIC instead of
>   arbitrary AXI_PWMGEN_TEST_DATA in AXI_PWMGEN_REG_SCRATCHPAD
> * Remove redundant clk struct from axi_pwmgen_ddata
> * Add self as module author
> * Add major version check for IP core
> ---
>  MAINTAINERS                  |   1 +
>  drivers/pwm/Kconfig          |  13 ++
>  drivers/pwm/Makefile         |   1 +
>  drivers/pwm/pwm-axi-pwmgen.c | 244 +++++++++++++++++++++++++++++++++++
>  4 files changed, 259 insertions(+)
>  create mode 100644 drivers/pwm/pwm-axi-pwmgen.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 8a4ed5545680..2baa7a0a1c8c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3438,6 +3438,7 @@ L:	linux-pwm@xxxxxxxxxxxxxxx
>  S:	Supported
>  W:	https://ez.analog.com/linux-software-drivers
>  F:	Documentation/devicetree/bindings/pwm/adi,axi-pwmgen.yaml
> +F:	drivers/pwm/pwm-axi-pwmgen.c
>  
>  AXXIA I2C CONTROLLER
>  M:	Krzysztof Adamski <krzysztof.adamski@xxxxxxxxx>
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 4b956d661755..d44b0e86adee 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -98,6 +98,19 @@ config PWM_ATMEL_TCB
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-atmel-tcb.
>  
> +config PWM_AXI_PWMGEN
> +	tristate "Analog Devices AXI PWM generator"
> +	depends on MICROBLAZE || NIOS2 || ARCH_ZYNQ || ARCH_ZYNQMP || ARCH_INTEL_SOCFPGA || COMPILE_TEST
> +	select REGMAP_MMIO
> +	help
> +	  This enables support for the Analog Devices AXI PWM generator.
> +
> +	  This is a configurable PWM generator with variable pulse width and
> +	  period.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called pwm-axi-pwmgen.
> +
>  config PWM_BCM_IPROC
>  	tristate "iProc PWM support"
>  	depends on ARCH_BCM_IPROC || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index c5ec9e168ee7..8322089954e9 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_PWM_APPLE)		+= pwm-apple.o
>  obj-$(CONFIG_PWM_ATMEL)		+= pwm-atmel.o
>  obj-$(CONFIG_PWM_ATMEL_HLCDC_PWM)	+= pwm-atmel-hlcdc.o
>  obj-$(CONFIG_PWM_ATMEL_TCB)	+= pwm-atmel-tcb.o
> +obj-$(CONFIG_PWM_AXI_PWMGEN)	+= pwm-axi-pwmgen.o
>  obj-$(CONFIG_PWM_BCM_IPROC)	+= pwm-bcm-iproc.o
>  obj-$(CONFIG_PWM_BCM_KONA)	+= pwm-bcm-kona.o
>  obj-$(CONFIG_PWM_BCM2835)	+= pwm-bcm2835.o
> diff --git a/drivers/pwm/pwm-axi-pwmgen.c b/drivers/pwm/pwm-axi-pwmgen.c
> new file mode 100644
> index 000000000000..0c8f7f893a21
> --- /dev/null
> +++ b/drivers/pwm/pwm-axi-pwmgen.c
> @@ -0,0 +1,244 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Analog Devices AXI PWM generator
> + *
> + * Copyright 2024 Analog Devices Inc.
> + * Copyright 2024 Baylibre SAS
> + *
> + * Limitations:
> + * - The writes to registers for period and duty are shadowed until
> + *   LOAD_CONFIG is written to AXI_PWMGEN_REG_CONFIG at the end of the
> + *   current period.

This implies that a currently running period is completed before the new
settings get active, right?

> + * - Writing LOAD_CONFIG also has the effect of re-synchronizing all
> + *   enabled channels, which could cause glitching on other channels. It
> + *   is therefore expected that channels are assigned harmonic periods
> + *   and all have a single user coordinating this.

What does "re-synchronize" mean here? Are all counters reset to zero?
"harmonic" means that all channels should use the same period length?

> + * - Supports normal polarity. Does not support changing polarity.

Please add an item documenting how the HW behaves on disable. (Typical
behaviours are "freeze" or "inactive".)

> + */
> +#include <linux/bits.h>
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <linux/fpga/adi-axi-common.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +
> +#define AXI_PWMGEN_REG_CORE_VERSION	0x00
> +#define AXI_PWMGEN_REG_ID		0x04
> +#define AXI_PWMGEN_REG_SCRATCHPAD	0x08
> +#define AXI_PWMGEN_REG_CORE_MAGIC	0x0C
> +#define AXI_PWMGEN_REG_CONFIG		0x10
> +#define AXI_PWMGEN_REG_NPWM		0x14
> +#define AXI_PWMGEN_CHX_PERIOD(ch)	(0x40 + (12 * (ch)))
> +#define AXI_PWMGEN_CHX_DUTY(ch)		(0x44 + (12 * (ch)))
> +#define AXI_PWMGEN_CHX_OFFSET(ch)	(0x48 + (12 * (ch)))

Reading https://wiki.analog.com/resources/fpga/docs/axi_pwm_gen I would
have expected:

	/* ch in { 0, ... 15 } */
	#define AXI_PWMGEN_REG_PULSE_X_PERIOD(ch)	(0x40 + 4 * (ch))
	#define AXI_PWMGEN_REG_PULSE_X_WIDTH(ch)	(0x80 + 4 * (ch))
	#define AXI_PWMGEN_REG_PULSE_X_OFFSET		(0xc0 + 4 * (ch))

> +#define AXI_PWMGEN_REG_CORE_MAGIC_VAL	0x601A3471 /* Identification number to test during setup */
> +#define AXI_PWMGEN_LOAD_CONFIG		BIT(1)
> +#define AXI_PWMGEN_RESET		BIT(0)

I'm a fan of including the register name in bitfield definitions. So
maybe:

	#define AXI_PWMGEN_REG_CONFIG_RESET	BIT(0)

> +struct axi_pwmgen_ddata {
> +	struct regmap *regmap;
> +	unsigned long clk_rate_hz;
> +};
> +
> +static const struct regmap_config axi_pwmgen_regmap_config = {
> +	.reg_bits = 32,
> +	.reg_stride = 4,
> +	.val_bits = 32,
> +};
> +
> +static int axi_pwmgen_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			    const struct pwm_state *state)
> +{
> +	struct axi_pwmgen_ddata *ddata = pwmchip_get_drvdata(chip);
> +	unsigned int ch = pwm->hwpwm;
> +	struct regmap *regmap = ddata->regmap;
> +	u64 period_cnt, duty_cnt;
> +	int ret;
> +
> +	if (state->polarity != PWM_POLARITY_NORMAL)
> +		return -EINVAL;
> +
> +	if (state->enabled) {
> +		period_cnt = mul_u64_u64_div_u64(state->period, ddata->clk_rate_hz, NSEC_PER_SEC);
> +		if (period_cnt > UINT_MAX)
> +			period_cnt = UINT_MAX;
> +
> +		if (period_cnt == 0)
> +			return -EINVAL;
> +
> +		ret = regmap_write(regmap, AXI_PWMGEN_CHX_PERIOD(ch), period_cnt);
> +		if (ret)
> +			return ret;
> +
> +		duty_cnt = mul_u64_u64_div_u64(state->duty_cycle, ddata->clk_rate_hz, NSEC_PER_SEC);
> +		if (duty_cnt > UINT_MAX)
> +			duty_cnt = UINT_MAX;
> +
> +		ret = regmap_write(regmap, AXI_PWMGEN_CHX_DUTY(ch), duty_cnt);
> +		if (ret)
> +			return ret;
> +	} else {
> +		ret = regmap_write(regmap, AXI_PWMGEN_CHX_PERIOD(ch), 0);
> +		if (ret)
> +			return ret;
> +
> +		ret = regmap_write(regmap, AXI_PWMGEN_CHX_DUTY(ch), 0);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return regmap_write(regmap, AXI_PWMGEN_REG_CONFIG, AXI_PWMGEN_LOAD_CONFIG);
> +}
> +
> +static int axi_pwmgen_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> +				struct pwm_state *state)
> +{
> +	struct axi_pwmgen_ddata *ddata = pwmchip_get_drvdata(chip);
> +	struct regmap *regmap = ddata->regmap;
> +	unsigned int ch = pwm->hwpwm;
> +	u32 cnt;
> +	int ret;
> +
> +	ret = regmap_read(regmap, AXI_PWMGEN_CHX_PERIOD(ch), &cnt);
> +	if (ret)
> +		return ret;
> +
> +	state->enabled = cnt != 0;
> +
> +	state->period = DIV_ROUND_UP_ULL((u64)cnt * NSEC_PER_SEC, ddata->clk_rate_hz);
> +
> +	ret = regmap_read(regmap, AXI_PWMGEN_CHX_DUTY(ch), &cnt);
> +	if (ret)
> +		return ret;
> +
> +	state->duty_cycle = DIV_ROUND_UP_ULL((u64)cnt * NSEC_PER_SEC, ddata->clk_rate_hz);
> +
> +	state->polarity = PWM_POLARITY_NORMAL;
> +
> +	return 0;
> +}
> +
> +static const struct pwm_ops axi_pwmgen_pwm_ops = {
> +	.apply = axi_pwmgen_apply,
> +	.get_state = axi_pwmgen_get_state,
> +};
> +
> +static int axi_pwmgen_setup(struct regmap *regmap, struct device *dev)
> +{
> +	int ret;
> +	u32 val;
> +
> +	ret = regmap_read(regmap, AXI_PWMGEN_REG_CORE_MAGIC, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val != AXI_PWMGEN_REG_CORE_MAGIC_VAL)
> +		return dev_err_probe(dev, -ENODEV,
> +			"failed to read expected value from register: got %08x, expected %08x\n",
> +			val,
> +			AXI_PWMGEN_REG_CORE_MAGIC_VAL);
> +
> +	ret = regmap_read(regmap, AXI_PWMGEN_REG_CORE_VERSION, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (ADI_AXI_PCORE_VER_MAJOR(val) != 1) {
> +		return dev_err_probe(dev, -ENODEV, "Unsupported peripheral version %u.%u.%u\n",
> +			ADI_AXI_PCORE_VER_MAJOR(val),
> +			ADI_AXI_PCORE_VER_MINOR(val),
> +			ADI_AXI_PCORE_VER_PATCH(val));
> +	}
> +
> +	/* Enable the core */
> +	ret = regmap_update_bits(regmap, AXI_PWMGEN_REG_CONFIG, AXI_PWMGEN_RESET, 0);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_read(regmap, AXI_PWMGEN_REG_NPWM, &val);
> +	if (ret)
> +		return ret;
> +
> +	/* Return the number of PWMs */
> +	return val;
> +}
> +
> +static void axi_pwmgen_clk_rate_exclusive_put(void *data)
> +{
> +	clk_rate_exclusive_put(data);
> +}
> +
> +static int axi_pwmgen_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct regmap *regmap;
> +	struct pwm_chip *chip;
> +	struct axi_pwmgen_ddata *ddata;
> +	struct clk *clk;
> +	void __iomem *io_base;
> +	int ret;
> +
> +	io_base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(io_base))
> +		return PTR_ERR(io_base);
> +
> +	regmap = devm_regmap_init_mmio(dev, io_base, &axi_pwmgen_regmap_config);
> +	if (IS_ERR(regmap))
> +		return dev_err_probe(dev, PTR_ERR(regmap),
> +				     "failed to init register map\n");
> +
> +	ret = axi_pwmgen_setup(regmap, dev);
> +	if (ret < 0)
> +		return ret;
> +
> +	chip = devm_pwmchip_alloc(dev, ret, sizeof(*ddata));
> +	if (IS_ERR(chip))
> +		return PTR_ERR(chip);
> +	ddata = pwmchip_get_drvdata(chip);
> +	ddata->regmap = regmap;
> +
> +	clk = devm_clk_get_enabled(dev, NULL);
> +	if (IS_ERR(clk))
> +		return dev_err_probe(dev, PTR_ERR(clk), "failed to get clock\n");
> +
> +	ret = clk_rate_exclusive_get(clk);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to get exclusive rate\n");
> +
> +	ret = devm_add_action_or_reset(dev, axi_pwmgen_clk_rate_exclusive_put, clk);
> +	if (ret)
> +		return ret;

There is a devm variant of clk_rate_exclusive_get() in the meantime.

> +	ddata->clk_rate_hz = clk_get_rate(clk);
> +	if (!ddata->clk_rate_hz || ddata->clk_rate_hz > NSEC_PER_SEC)
> +		return dev_err_probe(dev, -EINVAL,
> +				     "Invalid clock rate: %lu\n", ddata->clk_rate_hz);
> +
> +	chip->ops = &axi_pwmgen_pwm_ops;
> +	chip->atomic = true;
> +
> +	return devm_pwmchip_add(dev, chip);

Error message in case devm_pwmchip_add fails, please.

> +}

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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