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Date: Wed, 14 Sep 2022 18:47:20 +0200
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Ben Dooks <ben.dooks@...ive.com>
Cc: linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
Thierry Reding <thierry.reding@...il.com>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Greentime Hu <greentime.hu@...ive.com>,
jarkko.nikula@...ux.intel.com,
William Salmon <william.salmon@...ive.com>,
Jude Onyenegecha <jude.onyenegecha@...ive.com>
Subject: Re: [RFC v4 08/10] pwm: dwc: add of/platform support
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@...ive.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@...ive.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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