Re: [RFC v4 08/10] pwm: dwc: add of/platform support

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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On Tue, Aug 16, 2022 at 10:14:52PM +0100, Ben Dooks wrote:
> The dwc pwm controller can be used in non-PCI systems, so allow
> either platform or OF based probing.
> 
> Signed-off-by: Ben Dooks <ben.dooks@sifive.com>
> ---
> v4:
>  - split the of code out of the core
>  - moved the compile test code earlier
>  - fixed review comments
>   - used NS_PER_SEC
>   - use devm_clk_get_enabled
> v3:
>  - changed compatible name
> ---
>  drivers/pwm/Kconfig      |  9 +++++
>  drivers/pwm/Makefile     |  1 +
>  drivers/pwm/pwm-dwc-of.c | 78 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 88 insertions(+)
>  create mode 100644 drivers/pwm/pwm-dwc-of.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index a9f1c554db2b..f1735653365f 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -192,6 +192,15 @@ config PWM_DWC_PCI
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-dwc-pci.
>  
> +config PWM_DWC_OF
> +	tristate "DesignWare PWM Controller (OF bus)
> +	depends on PWM_DWC && OF
> +	help
> +	  PWM driver for Synopsys DWC PWM Controller on an OF bus.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-dwc-of.
> +
>  config PWM_EP93XX
>  	tristate "Cirrus Logic EP93xx PWM support"
>  	depends on ARCH_EP93XX || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index a70d36623129..d1fd1641f077 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -15,6 +15,7 @@ obj-$(CONFIG_PWM_CLPS711X)	+= pwm-clps711x.o
>  obj-$(CONFIG_PWM_CRC)		+= pwm-crc.o
>  obj-$(CONFIG_PWM_CROS_EC)	+= pwm-cros-ec.o
>  obj-$(CONFIG_PWM_DWC)		+= pwm-dwc.o
> +obj-$(CONFIG_PWM_DWC_OF)	+= pwm-dwc-of.o
>  obj-$(CONFIG_PWM_DWC_PCI)	+= pwm-dwc-pci.o
>  obj-$(CONFIG_PWM_EP93XX)	+= pwm-ep93xx.o
>  obj-$(CONFIG_PWM_FSL_FTM)	+= pwm-fsl-ftm.o
> diff --git a/drivers/pwm/pwm-dwc-of.c b/drivers/pwm/pwm-dwc-of.c
> new file mode 100644
> index 000000000000..d18fac287325
> --- /dev/null
> +++ b/drivers/pwm/pwm-dwc-of.c
> @@ -0,0 +1,78 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * DesignWare PWM Controller driver OF
> + *
> + * Copyright (C) 2022 SiFive, Inc.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/export.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/clk.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/pwm.h>
> +#include <linux/io.h>
> +
> +#include "pwm-dwc.h"
> +
> +static int dwc_pwm_plat_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct dwc_pwm *dwc;
> +	int ret;
> +
> +	dwc = dwc_pwm_alloc(dev);
> +	if (!dwc)
> +		return -ENOMEM;
> +
> +	dwc->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(dwc->base))
> +		return dev_err_probe(dev, PTR_ERR(dwc->base),
> +				     "failed to map IO\n");

devm_platform_ioremap_resource() already emits an error message.

> +
> +	dwc->clk = devm_clk_get_enabled(dev, "timer");
> +	if (IS_ERR(dwc->clk))
> +		return dev_err_probe(dev, PTR_ERR(dwc->clk),
> +				     "failed to get timer clock\n");
> +
> +	clk_prepare_enable(dwc->clk);

You don't need clk_prepare_enable() as you used devm_clk_get_enabled().

(Otherwise, when keeping clk_prepare_enable() you need to check the
return value.)

> +	dwc->clk_ns = NSEC_PER_SEC / clk_get_rate(dwc->clk);

I think I already pointed out this is non-optimal.

Later you use clk_ns in __dwc_pwm_configure_timer():

	tmp = DIV_ROUND_CLOSEST_ULL(state->duty_cycle, dwc->clk_ns);

So what you really want here is:

	tmp = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * clk_get_rate(dwc->clk), NSEC_PER_SEC);

With for example clk_get_rate(dwc->clk) = 201171875 and duty_cycle =
4096 you now get clk_ns = 4 (while the exact value is 4.97087..), tmp =
1024, while the exact value is 824.

So the idea is to add a clkrate member to the private driver struct, let
it default to 100000000 for the pci case and use the line I suggested
above.

> +
> +	ret = devm_pwmchip_add(dev, &dwc->chip);
> +	if (ret)
> +		return ret;
> +
> +	return 0;

This is equivalent to

	return ret;

> +}
> +
> +static int dwc_pwm_plat_remove(struct platform_device *pdev)
> +{
> +	struct dwc_pwm *dwc = platform_get_drvdata(pdev);
> +
> +	clk_disable_unprepare(dwc->clk);
> +	return 0;
> +}

When dropping clk_prepare_enable() the .remove callback can go away,
too.

> +
> +static const struct of_device_id dwc_pwm_dt_ids[] = {
> +	{ .compatible = "snps,dw-apb-timers-pwm2" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, dwc_pwm_dt_ids);
> +
> +static struct platform_driver dwc_pwm_plat_driver = {
> +	.driver = {
> +		.name		= "dwc-pwm",
> +		.of_match_table  = dwc_pwm_dt_ids,
> +	},
> +	.probe	= dwc_pwm_plat_probe,
> +	.remove	= dwc_pwm_plat_remove,
> +};
> +
> +module_platform_driver(dwc_pwm_plat_driver);
> +
> +MODULE_ALIAS("platform:dwc-pwm-of");
> +MODULE_AUTHOR("Ben Dooks <ben.dooks@sifive.com>");
> +MODULE_DESCRIPTION("DesignWare PWM Controller");
> +MODULE_LICENSE("GPL");

Best regards
Uwe

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

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