Message-ID: <20220614123436.ahimxsfkwmfdjqdw@pengutronix.de>
Date:   Tue, 14 Jun 2022 14:34:36 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 1/2] pwm: add microchip soft ip corePWM driver

Hello,

On Mon, Jun 13, 2022 at 12:17:59PM +0100, Conor Dooley wrote:
> Add a driver that supports the Microchip FPGA "soft" PWM IP core.
> 
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> ---
>  drivers/pwm/Kconfig              |  10 +
>  drivers/pwm/Makefile             |   1 +
>  drivers/pwm/pwm-microchip-core.c | 310 +++++++++++++++++++++++++++++++
>  3 files changed, 321 insertions(+)
>  create mode 100644 drivers/pwm/pwm-microchip-core.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 21e3b05a5153..a651848e444b 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -383,6 +383,16 @@ config PWM_MEDIATEK
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-mediatek.
>  
> +config PWM_MICROCHIP_CORE
> +	tristate "Microchip corePWM PWM support"
> +	depends on SOC_MICROCHIP_POLARFIRE || COMPILE_TEST
> +	depends on HAS_IOMEM && OF
> +	help
> +	  PWM driver for Microchip FPGA soft IP core.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-microchip-core.
> +
>  config PWM_MXS
>  	tristate "Freescale MXS PWM support"
>  	depends on ARCH_MXS || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 708840b7fba8..d29754c20f91 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -33,6 +33,7 @@ obj-$(CONFIG_PWM_LPSS_PCI)	+= pwm-lpss-pci.o
>  obj-$(CONFIG_PWM_LPSS_PLATFORM)	+= pwm-lpss-platform.o
>  obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o
>  obj-$(CONFIG_PWM_MEDIATEK)	+= pwm-mediatek.o
> +obj-$(CONFIG_PWM_MICROCHIP_CORE)	+= pwm-microchip-core.o
>  obj-$(CONFIG_PWM_MTK_DISP)	+= pwm-mtk-disp.o
>  obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o
>  obj-$(CONFIG_PWM_NTXEC)		+= pwm-ntxec.o
> diff --git a/drivers/pwm/pwm-microchip-core.c b/drivers/pwm/pwm-microchip-core.c
> new file mode 100644
> index 000000000000..d2abc46deec4
> --- /dev/null
> +++ b/drivers/pwm/pwm-microchip-core.c
> @@ -0,0 +1,310 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * corePWM driver for Microchip "soft" FPGA IP cores.
> + *
> + * Copyright (c) 2021-2022 Microchip Corporation. All rights reserved.
> + * Author: Conor Dooley <conor.dooley@...rochip.com>
> + * Documentation:
> + * https://www.microsemi.com/document-portal/doc_download/1245275-corepwm-hb
> + *
> + * Limitations:
> + * - If the IP block is configured without "shadow registers", all register
> + *   writes will take effect immediately, causing glitches on the output.
> + *   If shadow registers *are* enabled, a write to the "SYNC_UPDATE" register
> + *   notifies the core that it needs to update the registers defining the
> + *   waveform from the contents of the "shadow registers".
> + * - The IP block has no concept of a duty cycle, only rising/falling edges of
> + *   the waveform. Unfortunately, if the rising & falling edges registers have
> + *   the same value written to them the IP block will do whichever of a rising
> + *   or a falling edge is possible. I.E. a 50% waveform at twice the requested
> + *   period. Therefore to get a 0% waveform, the output is set the max high/low
> + *   time depending on polarity.
> + * - The PWM period is set for the whole IP block not per channel. The driver
> + *   will only change the period if no other PWM output is enabled.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/math.h>
> +
> +#define PREG_TO_VAL(PREG) ((PREG) + 1)
> +
> +#define COREPWM_PRESCALE_REG	0x00u
> +#define COREPWM_PERIOD_REG	0x04u
> +#define COREPWM_EN_LOW_REG	0x08u
> +#define COREPWM_EN_HIGH_REG	0x0Cu
> +#define COREPWM_SYNC_UPD_REG	0xE4u
> +#define COREPWM_POSEDGE_OFFSET	0x10u
> +#define COREPWM_NEGEDGE_OFFSET	0x14u
> +#define COREPWM_CHANNEL_OFFSET	0x08u
> +
> +struct mchp_core_pwm_chip {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	void __iomem *base;
> +};
> +
> +static inline struct mchp_core_pwm_chip *to_mchp_core_pwm(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct mchp_core_pwm_chip, chip);
> +}
> +
> +static void mchp_core_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm, bool enable)
> +{
> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
> +	u8 channel_enable, reg_offset, shift;
> +
> +	/*
> +	 * There are two adjacent 8 bit control regs, the lower reg controls
> +	 * 0-7 and the upper reg 8-15. Check if the pwm is in the upper reg
> +	 * and if so, offset by the bus width.
> +	 */
> +	reg_offset = COREPWM_EN_LOW_REG + (pwm->hwpwm >> 3) * sizeof(u32);
> +	shift = pwm->hwpwm > 7 ? pwm->hwpwm - 8 : pwm->hwpwm;
> +
> +	channel_enable = readb_relaxed(mchp_core_pwm->base + reg_offset);
> +	channel_enable &= ~(1 << shift);
> +	channel_enable |= (enable << shift);
> +
> +	writel_relaxed(channel_enable, mchp_core_pwm->base + reg_offset);
> +}
> +
> +static void mchp_core_pwm_apply_duty(struct pwm_chip *chip,  struct pwm_device *pwm,
> +				     const struct pwm_state *state)
> +{
> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
> +	void __iomem *channel_base = mchp_core_pwm->base + pwm->hwpwm * COREPWM_CHANNEL_OFFSET;
> +	u64 duty_steps, period, tmp;
> +	u8 prescale, period_steps, posedge, negedge;
> +
> +	prescale = PREG_TO_VAL(readb_relaxed(mchp_core_pwm->base + COREPWM_PRESCALE_REG));
> +	period_steps = PREG_TO_VAL(readb_relaxed(mchp_core_pwm->base + COREPWM_PERIOD_REG));
> +	period = period_steps * prescale * NSEC_PER_SEC;
> +	period = div64_u64(period, clk_get_rate(mchp_core_pwm->clk));
> +
> +	/*
> +	 * Calculate the duty cycle in multiples of the prescaled period:
> +	 * duty_steps = duty_in_ns / step_in_ns
> +	 * step_in_ns = (prescale * NSEC_PER_SEC) / clk_rate
> +	 * The code below is rearranged slightly to only divide once.
> +	 *
> +	 * Because the period is per channel, it is possible that the requested
> +	 * duty cycle is longer than the period, in which case cap it to the
> +	 * period.
> +	 */
> +	if (state->duty_cycle > period) {
> +		duty_steps = period_steps;
> +	} else {
> +		duty_steps = state->duty_cycle * clk_get_rate(mchp_core_pwm->clk);
> +		tmp = prescale * NSEC_PER_SEC;
> +		duty_steps = div64_u64(duty_steps, tmp);
> +	}
> +
> +	/*
> +	 * Turn the output on unless posedge == negedge, in which case the
> +	 * duty is intended to be 0, but limitations of the IP block don't
> +	 * allow a zero length duty cycle - so just set the max high/low time
> +	 * respectively.
> +	 */
> +	if (state->polarity == PWM_POLARITY_INVERSED) {
> +		negedge = !duty_steps ? period_steps : 0u;
> +		posedge = duty_steps;
> +	} else {
> +		posedge = !duty_steps ? period_steps : 0u;
> +		negedge = duty_steps;
> +	}
> +
> +	writel_relaxed(posedge, channel_base + COREPWM_POSEDGE_OFFSET);
> +	writel_relaxed(negedge, channel_base + COREPWM_NEGEDGE_OFFSET);
> +}
> +
> +static void mchp_core_pwm_apply_period(struct pwm_chip *chip, const struct pwm_state *state)
> +{
> +	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
> +	u64 tmp = state->period;
> +	u8 prescale, period_steps;
> +
> +	/*
> +	 * Calculate the period cycles and prescale values.
> +	 * The registers are each 8 bits wide & multiplied to compute the period
> +	 * so the maximum period that can be generated is 0xFFFF times the period
> +	 * of the input clock.
> +	 */
> +	tmp *= clk_get_rate(mchp_core_pwm->clk);
> +	do_div(tmp, NSEC_PER_SEC);
> +
> +	if (tmp > 0xFFFFu) {
> +		prescale = 0xFFu;
> +		period_steps = 0xFFu;
> +	} else {
> +		prescale = tmp >> 8;
> +		period_steps = tmp / PREG_TO_VAL(prescale) - 1;

Here is the 64bit division.

Best regards
Uwe

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

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