Re: [PATCH v2 1/2] pwm: add microchip soft ip corePWM driver

[<Conor.Dooley@microchip.com>]

On 14/06/2022 13:34, Uwe Kleine-König wrote:
> 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@microchip.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@microchip.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.
> 

Thanks :)
I would prob have missed that too, since I was thinking div /by/ > int.


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