Re: [PATCH v3 2/2] pwm: Add Broadcom BCM7038 PWM controller support

From: Ariel D'Alessandro
Date: Mon Sep 07 2015 - 15:15:38 EST

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Hi Florian,

I wrote some observations below that maybe can be useful.

El 28/08/15 a las 22:21, Florian Fainelli escribió:
> Add support for the BCM7038-style PWM controller found in all BCM7xxx STB SoCs.
> This controller has a hardcoded 2 channels per controller, and cascades a
> variable frequency generator on top of a fixed frequency generator which offers
> a range of a 148ns period all the way to ~622ms periods.
>
> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> ---
> Changes in v3:
>
> - make clock mandatory
> - removed a remaining div64_u64 use
>
> hanges in v2:
>
> - properly format comments
> - utilize do_div instead of div64_u64
> - avoid using a "done" variable for the while loop
> - utilize a parameterized register accessor
> - remove a bunch of unnecessary assignments
> - provide a module author
> - update depends to build on BMIPS_GENERIC (the other user)
> - removed artificial padding
> - removed used only once variable: dn
> - utilize devm_ioremap_resource
> - do not print success message
> - removed THIS_MODULE from platform_driver structure
>
> drivers/pwm/Kconfig | 10 ++
> drivers/pwm/Makefile | 1 +
> drivers/pwm/pwm-brcmstb.c | 324 ++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 335 insertions(+)
> create mode 100644 drivers/pwm/pwm-brcmstb.c
>
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index b1541f40fd8d..363c22b22071 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -111,6 +111,16 @@ config PWM_CLPS711X
> To compile this driver as a module, choose M here: the module
> will be called pwm-clps711x.
>
> +config PWM_BRCMSTB
> + tristate "Broadcom STB PWM support"
> + depends on ARCH_BRCMSTB || BMIPS_GENERIC
> + help
> + Generic PWM framework driver for the Broadcom Set-top-Box
> + SoCs (BCM7xxx).
> +
> + To compile this driver as a module, choose M Here: the module
> + will be called pwm-brcmstb.c.
> +
> config PWM_EP93XX
> tristate "Cirrus Logic EP93xx PWM support"
> depends on ARCH_EP93XX
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index ec50eb5b5a8f..dc7b1b82d47e 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_PWM_ATMEL_TCB) += pwm-atmel-tcb.o
> obj-$(CONFIG_PWM_BCM_KONA) += pwm-bcm-kona.o
> obj-$(CONFIG_PWM_BCM2835) += pwm-bcm2835.o
> obj-$(CONFIG_PWM_BFIN) += pwm-bfin.o
> +obj-$(CONFIG_PWM_BRCMSTB) += pwm-brcmstb.o
> obj-$(CONFIG_PWM_CLPS711X) += pwm-clps711x.o
> obj-$(CONFIG_PWM_EP93XX) += pwm-ep93xx.o
> obj-$(CONFIG_PWM_FSL_FTM) += pwm-fsl-ftm.o
> diff --git a/drivers/pwm/pwm-brcmstb.c b/drivers/pwm/pwm-brcmstb.c
> new file mode 100644
> index 000000000000..9ea73755f281
> --- /dev/null
> +++ b/drivers/pwm/pwm-brcmstb.c
> @@ -0,0 +1,324 @@
> +/*
> + * Broadcom BCM7038 PWM driver
> + * Author: Florian Fainelli
> + *
> + * Copyright (C) 2015 Broadcom Corporation
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/clk.h>
> +#include <linux/export.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +
> +#define PWM_CTRL 0x00
> +#define CTRL_START BIT(0)
> +#define CTRL_OEB BIT(1)
> +#define CTRL_FORCE_HIGH BIT(2)
> +#define CTRL_OPENDRAIN BIT(3)
> +#define CTRL_CHAN_OFFS 4
> +
> +#define PWM_CTRL2 0x04
> +#define CTRL2_OUT_SELECT BIT(0)
> +
> +#define PWM_CWORD_MSB 0x08
> +#define PWM_CWORD_LSB 0x0C
> +
> +#define PWM_CH_SIZE 0x8
> +
> +/* Number of bits for the CWORD value */
> +#define CWORD_BIT_SIZE 16
> +
> +/*
> + * Maximum control word value allowed when variable-frequency PWM is used as a
> + * clock for the constant-frequency PMW.
> + */
> +#define CONST_VAR_F_MAX 32768
> +#define CONST_VAR_F_MIN 1
> +
> +#define PWM_ON(ch) (0x18 + ((ch) * PWM_CH_SIZE))
> +#define PWM_ON_MIN 1
> +#define PWM_PERIOD(ch) (0x1C + ((ch) * PWM_CH_SIZE))
> +#define PWM_PERIOD_MIN 0
> +
> +#define PWM_ON_PERIOD_MAX 0xff
> +
> +struct brcmstb_pwm_dev {
> + void __iomem *base;
> + struct clk *clk;
> + struct pwm_chip chip;
> +};
> +
> +static inline u32 pwm_readl(struct brcmstb_pwm_dev *p, u32 off)

The function name 'pwm_readl' sounds to be very common. It might be
better to use a prefix here, don't you think? Maybe brcmstb_pwm_readl?

> +{
> + if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
> + return __raw_readl(p->base + off);
> + else
> + return readl_relaxed(p->base + off);
> +}
> +
> +static inline void pwm_writel(struct brcmstb_pwm_dev *p, u32 val, u32 off)

Same as before here.

> +{
> + if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
> + __raw_writel(val, p->base + off);
> + else
> + writel_relaxed(val, p->base + off);
> +}
> +
> +static inline struct brcmstb_pwm_dev *to_brcmstb_pwm(struct pwm_chip *ch)
> +{
> + return container_of(ch, struct brcmstb_pwm_dev, chip);
> +}
> +
> +/*
> + * Fv is derived from the variable frequency output. The variable frequency
> + * output is configured using this formula:
> + *
> + * W = cword, if cword < 2 ^ 15 else 16-bit 2's complement of cword
> + *
> + * Fv = W x 2 ^ -16 x 27Mhz (reference clock)
> + *
> + * The period is: (period + 1) / Fv and "on" time is on / (period + 1)
> + *
> + * The PWM core framework specifies that the "duty_ns" parameter is in fact the
> + * "on" time, so this translates directly into our HW programming here.
> + */
> +static int brcmstb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> + int duty_ns, int period_ns)
> +{
> + struct brcmstb_pwm_dev *b = to_brcmstb_pwm(chip);
> + unsigned long pc, dc, cword = CONST_VAR_F_MAX;
> + unsigned int ch = pwm->hwpwm;
> + u64 val, rate;
> + u32 reg;
> +
> + /*
> + * If asking for a duty_ns equal to period_ns, we need to substract
> + * the period value by 1 to make it shorter than the "on" time and
> + * produce a flat 100% duty cycle signal, and max out the "on" time
> + */
> + if (duty_ns == period_ns) {
> + dc = PWM_ON_PERIOD_MAX;
> + pc = PWM_ON_PERIOD_MAX - 1;
> + goto done;
> + }
> +
> + while (1) {
> + /*
> + * Calculate the base rate from base frequency and current
> + * cword
> + */
> + rate = (u64)clk_get_rate(b->clk) * (u64)cword;
> + do_div(rate, 1 << CWORD_BIT_SIZE);
> +
> + val = period_ns * rate;
> + do_div(val, NSEC_PER_SEC);
> + pc = val;
> +
> + val = (duty_ns + 1) * rate;
> + do_div(val, NSEC_PER_SEC);
> + dc = val;
> +
> + /*
> + * We can be called with separate duty and period updates,
> + * so do not reject dc == 0 right away
> + */
> + if (pc == PWM_PERIOD_MIN ||
> + (dc < PWM_ON_MIN && duty_ns))

No break needed here, this expression can be written on a single line
increasing readability.

> + return -EINVAL;
> +
> + /* We converged on a calculation */
> + if (pc <= PWM_ON_PERIOD_MAX && dc <= PWM_ON_PERIOD_MAX)
> + break;
> +
> + /*
> + * The cword needs to be a power of 2 for the variable
> + * frequency generator to output a 50% duty cycle variable
> + * frequency which is used as input clock to the fixed
> + * frequency generator.
> + */
> + cword >>= 1;
> +
> + /*
> + * Desired periods are too large, we do not have a divider
> + * for them
> + */
> + if (cword < CONST_VAR_F_MIN)
> + return -EINVAL;
> + }
> +
> +done:
> + /*
> + * Configure the defined "cword" value to have the variable frequency
> + * generator output a base frequency for the constant frequency
> + * generator to derive from.
> + */
> + pwm_writel(b, cword >> 8, PWM_CWORD_MSB + ch * PWM_CH_SIZE);
> + pwm_writel(b, cword & 0xff, PWM_CWORD_LSB + ch * PWM_CH_SIZE);
> +
> + /* Select constant frequency signal output */
> + reg = pwm_readl(b, PWM_CTRL2);
> + reg |= (CTRL2_OUT_SELECT << (ch * CTRL_CHAN_OFFS));

A nitpick here, outer parenthesis can be avoided.

> + pwm_writel(b, reg, PWM_CTRL2);

This read-modify-write sequence may be protected by some locking
mechanism. Notice that, as written in the docs: "PWM core does not
enforce any locking to pwm_enable(), pwm_disable() and pwm_config()".

> +
> + /* Configure on and period value */
> + pwm_writel(b, pc, PWM_PERIOD(ch));
> + pwm_writel(b, dc, PWM_ON(ch));
> +
> + return 0;
> +}
> +
> +static inline void brcmstb_pwm_enable_set(struct brcmstb_pwm_dev *b,
> + unsigned int ch, bool enable)
> +{
> + unsigned int ofs = ch * CTRL_CHAN_OFFS;
> + u32 reg;
> +
> + reg = pwm_readl(b, PWM_CTRL);
> + if (enable) {
> + reg &= ~(CTRL_OEB << ofs);
> + reg |= ((CTRL_START | CTRL_OPENDRAIN) << ofs);

Nit, outer parenthesis can be avoided.

> + } else {
> + reg &= ~((CTRL_START | CTRL_OPENDRAIN) << ofs);
> + reg |= (CTRL_OEB << ofs);

Also here.

> + }
> + pwm_writel(b, reg, PWM_CTRL);

Again, R-M-W sequence may be protected by some locking mechanism.

> +}
> +
> +static int brcmstb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> + struct brcmstb_pwm_dev *b = to_brcmstb_pwm(chip);
> +
> + brcmstb_pwm_enable_set(b, pwm->hwpwm, true);
> +
> + return 0;
> +}
> +
> +static void brcmstb_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> + struct brcmstb_pwm_dev *b = to_brcmstb_pwm(chip);
> +
> + brcmstb_pwm_enable_set(b, pwm->hwpwm, false);
> +}
> +
> +static const struct pwm_ops brcmstb_pwm_ops = {
> + .config = brcmstb_pwm_config,
> + .enable = brcmstb_pwm_enable,
> + .disable = brcmstb_pwm_disable,
> + .owner = THIS_MODULE,
> +};
> +
> +static const struct of_device_id brcmstb_pwm_of_match[] = {
> + { .compatible = "brcm,bcm7038-pwm", },
> + { /* sentinel */ }
> +};
> +
> +static int brcmstb_pwm_probe(struct platform_device *pdev)
> +{
> + struct brcmstb_pwm_dev *p;
> + struct resource *r;
> + int ret;
> +
> + p = devm_kzalloc(&pdev->dev, sizeof(*p), GFP_KERNEL);
> + if (!p)
> + return -ENOMEM;
> +
> + /*
> + * Try to grab the clock and its rate, if not available, default
> + * to the base 27Mhz clock domain this block comes from.
> + */
> + p->clk = devm_clk_get(&pdev->dev, NULL);
> + if (IS_ERR(p->clk)) {
> + dev_err(&pdev->dev, "failed to obtain clock\n");
> + return PTR_ERR(p->clk);
> + }
> +
> + clk_prepare_enable(p->clk);
> +
> + platform_set_drvdata(pdev, p);
> +
> + p->chip.dev = &pdev->dev;
> + p->chip.ops = &brcmstb_pwm_ops;
> + /* Dynamically assign a PWM base */
> + p->chip.base = -1;
> + /* Static number of PWM channels for this controller */
> + p->chip.npwm = 2;
> + p->chip.can_sleep = true;
> +
> + r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> + p->base = devm_ioremap_resource(&pdev->dev, r);
> + if (!p->base)
> + return -ENOMEM;

I think you're missing some cleanup routine here. You have a previous
call to clk_prepare_enable(), so you may have a call to
clk_disable_unprepare() here in order to exit cleanly.

> +
> + ret = pwmchip_add(&p->chip);
> + if (ret)
> + dev_err(&pdev->dev, "failed to add PWM chip %d\n", ret);

Cleanup needed here too.

> +
> + return ret;
> +}
> +
> +static int brcmstb_pwm_remove(struct platform_device *pdev)
> +{
> + struct brcmstb_pwm_dev *p = platform_get_drvdata(pdev);
> +
> + clk_disable_unprepare(p->clk);
> +
> + return pwmchip_remove(&p->chip);

AFAIK, pwmchip_remove() may return busy if the PWM chip provides a PWM
device that is still requested, so you shouldn't disable the clock
before you ensure the PWM chip has been successfuly removed.

It think you could do something like:

ret = pwmchip_remove(&p->chip);
if (ret)
return ret;

clk_disable_unprepare(p->clk);
return 0;

> +}
> +
> +#ifdef CONFIG_PM_SLEEP
> +static int brcmstb_pwm_suspend(struct device *d)
> +{
> + struct platform_device *pdev = to_platform_device(d);
> + struct brcmstb_pwm_dev *p = platform_get_drvdata(pdev);
> +
> + clk_disable(p->clk);
> +
> + return 0;
> +}
> +
> +static int brcmstb_pwm_resume(struct device *d)
> +{
> + struct platform_device *pdev = to_platform_device(d);
> + struct brcmstb_pwm_dev *p = platform_get_drvdata(pdev);
> +
> + clk_enable(p->clk);
> +
> + return 0;
> +}
> +#endif
> +
> +static SIMPLE_DEV_PM_OPS(brcmstb_pwm_pm_ops,
> + brcmstb_pwm_suspend, brcmstb_pwm_resume);
> +
> +static struct platform_driver brcmstb_pwm_driver = {
> + .probe = brcmstb_pwm_probe,
> + .remove = brcmstb_pwm_remove,
> + .driver = {
> + .name = "pwm-brcmstb",
> + .of_match_table = brcmstb_pwm_of_match,
> + .pm = &brcmstb_pwm_pm_ops,
> + },
> +};
> +module_platform_driver(brcmstb_pwm_driver);
> +
> +MODULE_AUTHOR("Florian Fainelli <f.fainelli@xxxxxxxxx>");
> +MODULE_DESCRIPTION("Broadcom STB PWM driver");
> +MODULE_ALIAS("platform:pwm-brcmstb");
> +MODULE_LICENSE("GPL");
>

--
Ariel D'Alessandro, VanguardiaSur
www.vanguardiasur.com.ar
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Next message: Jonathan Corbet: "[PATCH] locking/static_keys: fix a silly typo"
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