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Date: Wed, 14 Aug 2019 16:42:28 +0800
From: Baolin Wang <baolin.wang@...aro.org>
To: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
Cc: Thierry Reding <thierry.reding@...il.com>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Orson Zhai <orsonzhai@...il.com>,
Chunyan Zhang <zhang.lyra@...il.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
linux-pwm@...r.kernel.org, DTML <devicetree@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] pwm: sprd: Add Spreadtrum PWM support
Hi Uwe,
On Tue, 13 Aug 2019 at 23:16, Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>
> Hello,
>
> On Tue, Aug 13, 2019 at 09:46:41PM +0800, Baolin Wang wrote:
> > This patch adds the Spreadtrum PWM support, which provides maximum 4
> > channels.
> >
> > Signed-off-by: Neo Hou <neo.hou@...soc.com>
> > Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> > ---
> > Changes from v1:
> > - Add depending on HAS_IOMEM.
> > - Rename parameters' names.
> > - Implement .apply() instead of .config(), .enable() and .disable().
> > - Use NSEC_PER_SEC instead of 1000000000ULL.
> > - Add some comments to make code more readable.
> > - Remove some redundant operation.
> > - Use standard clock properties to set clock parent.
> > - Other coding style optimization.
> > ---
> > drivers/pwm/Kconfig | 11 ++
> > drivers/pwm/Makefile | 1 +
> > drivers/pwm/pwm-sprd.c | 307 ++++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 319 insertions(+)
> > create mode 100644 drivers/pwm/pwm-sprd.c
> >
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index a7e5751..31dfc88 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -423,6 +423,17 @@ config PWM_SPEAR
> > To compile this driver as a module, choose M here: the module
> > will be called pwm-spear.
> >
> > +config PWM_SPRD
> > + tristate "Spreadtrum PWM support"
> > + depends on ARCH_SPRD || COMPILE_TEST
> > + depends on HAS_IOMEM
> > + help
> > + Generic PWM framework driver for the PWM controller on
> > + Spreadtrum SoCs.
> > +
> > + To compile this driver as a module, choose M here: the module
> > + will be called pwm-sprd.
> > +
> > config PWM_STI
> > tristate "STiH4xx PWM support"
> > depends on ARCH_STI
> > diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> > index 76b555b..26326ad 100644
> > --- a/drivers/pwm/Makefile
> > +++ b/drivers/pwm/Makefile
> > @@ -41,6 +41,7 @@ obj-$(CONFIG_PWM_ROCKCHIP) += pwm-rockchip.o
> > obj-$(CONFIG_PWM_SAMSUNG) += pwm-samsung.o
> > obj-$(CONFIG_PWM_SIFIVE) += pwm-sifive.o
> > obj-$(CONFIG_PWM_SPEAR) += pwm-spear.o
> > +obj-$(CONFIG_PWM_SPRD) += pwm-sprd.o
> > obj-$(CONFIG_PWM_STI) += pwm-sti.o
> > obj-$(CONFIG_PWM_STM32) += pwm-stm32.o
> > obj-$(CONFIG_PWM_STM32_LP) += pwm-stm32-lp.o
> > diff --git a/drivers/pwm/pwm-sprd.c b/drivers/pwm/pwm-sprd.c
> > new file mode 100644
> > index 0000000..067e711
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-sprd.c
> > @@ -0,0 +1,307 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Spreadtrum Communications Inc.
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/math64.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/pwm.h>
> > +
> > +#define SPRD_PWM_PRESCALE 0x0
> > +#define SPRD_PWM_MOD 0x4
> > +#define SPRD_PWM_DUTY 0x8
> > +#define SPRD_PWM_ENABLE 0x18
> > +
> > +#define SPRD_PWM_MOD_MAX GENMASK(7, 0)
> > +#define SPRD_PWM_DUTY_MSK GENMASK(15, 0)
> > +#define SPRD_PWM_PRESCALE_MSK GENMASK(7, 0)
> > +#define SPRD_PWM_ENABLE_BIT BIT(0)
> > +
> > +#define SPRD_PWM_NUM 4
> > +#define SPRD_PWM_REGS_SHIFT 5
> > +#define SPRD_PWM_NUM_CLKS 2
> > +#define SPRD_PWM_OUTPUT_CLK 1
>
> These definitions could benefit from some explaining comments. Just from
> looking at the names it is for example not obvious what is the
> difference between SPRD_PWM_NUM and SPRD_PWM_NUM_CLKS is.
Sure, I will optimize the macros' names to make them understandable.
>
> > +struct sprd_pwm_chn {
> > + struct clk_bulk_data clks[SPRD_PWM_NUM_CLKS];
> > + u32 clk_rate;
> > +};
> > +
> > +struct sprd_pwm_chip {
> > + void __iomem *base;
> > + struct device *dev;
> > + struct pwm_chip chip;
> > + int num_pwms;
> > + struct sprd_pwm_chn chn[SPRD_PWM_NUM];
> > +};
> > +
> > +/*
> > + * The list of clocks required by PWM channels, and each channel has 2 clocks:
> > + * enable clock and pwm clock.
> > + */
> > +static const char * const sprd_pwm_clks[] = {
> > + "enable0", "pwm0",
> > + "enable1", "pwm1",
> > + "enable2", "pwm2",
> > + "enable3", "pwm3",
> > +};
> > +
> > +static u32 sprd_pwm_read(struct sprd_pwm_chip *spc, u32 hwid, u32 reg)
> > +{
> > + u32 offset = reg + (hwid << SPRD_PWM_REGS_SHIFT);
> > +
> > + return readl_relaxed(spc->base + offset);
> > +}
> > +
> > +static void sprd_pwm_write(struct sprd_pwm_chip *spc, u32 hwid,
> > + u32 reg, u32 val)
> > +{
> > + u32 offset = reg + (hwid << SPRD_PWM_REGS_SHIFT);
> > +
> > + writel_relaxed(val, spc->base + offset);
> > +}
> > +
> > +static void sprd_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct sprd_pwm_chip *spc =
> > + container_of(chip, struct sprd_pwm_chip, chip);
> > + struct sprd_pwm_chn *chn = &spc->chn[pwm->hwpwm];
> > + u32 val, duty, prescale;
> > + u64 tmp;
> > + int ret;
> > +
> > + /*
> > + * The clocks to PWM channel has to be enabled first before
> > + * reading to the registers.
> > + */
> > + ret = clk_bulk_prepare_enable(SPRD_PWM_NUM_CLKS, chn->clks);
> > + if (ret) {
> > + dev_err(spc->dev, "failed to enable pwm%u clocks\n",
> > + pwm->hwpwm);
> > + return;
> > + }
> > +
> > + val = sprd_pwm_read(spc, pwm->hwpwm, SPRD_PWM_ENABLE);
> > + if (val & SPRD_PWM_ENABLE_BIT)
> > + state->enabled = true;
> > + else
> > + state->enabled = false;
> > +
> > + /*
> > + * The hardware provides a counter that is feed by the source clock.
> > + * The period length is (PRESCALE + 1) * MOD counter steps.
> > + * The duty cycle length is (PRESCALE + 1) * DUTY counter steps.
> > + * Thus the period_ns and duty_ns calculation formula should be:
> > + * period_ns = NSEC_PER_SEC * (prescale + 1) * mod / clk_rate
> > + * duty_ns = NSEC_PER_SEC * (prescale + 1) * duty / clk_rate
> > + */
> > + val = sprd_pwm_read(spc, pwm->hwpwm, SPRD_PWM_PRESCALE);
> > + prescale = val & SPRD_PWM_PRESCALE_MSK;
> > + tmp = (prescale + 1) * NSEC_PER_SEC * SPRD_PWM_MOD_MAX;
> > + state->period = DIV_ROUND_CLOSEST_ULL(tmp, chn->clk_rate);
> > +
> > + val = sprd_pwm_read(spc, pwm->hwpwm, SPRD_PWM_DUTY);
> > + duty = val & SPRD_PWM_DUTY_MSK;
> > + tmp = (prescale + 1) * NSEC_PER_SEC * duty;
> > + state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, chn->clk_rate);
> > +
> > + /* Disable PWM clocks if the PWM channel is not in enable state. */
> > + if (!state->enabled)
> > + clk_bulk_disable_unprepare(SPRD_PWM_NUM_CLKS, chn->clks);
> > +}
> > +
> > +static int sprd_pwm_config(struct sprd_pwm_chip *spc, struct pwm_device *pwm,
> > + int duty_ns, int period_ns)
> > +{
> > + struct sprd_pwm_chn *chn = &spc->chn[pwm->hwpwm];
> > + u64 div, tmp;
> > + u32 prescale, duty;
> > +
> > + /*
> > + * The hardware provides a counter that is feed by the source clock.
> > + * The period length is (PRESCALE + 1) * MOD counter steps.
> > + * The duty cycle length is (PRESCALE + 1) * DUTY counter steps.
> > + *
> > + * To keep the maths simple we're always using MOD = SPRD_PWM_MOD_MAX.
> > + * The value for PRESCALE is selected such that the resulting period
> > + * gets the maximal length not bigger than the requested one with the
> > + * given settings (MOD = SPRD_PWM_MOD_MAX and input clock).
> > + */
> > + duty = duty_ns * SPRD_PWM_MOD_MAX / period_ns;
> > +
> > + tmp = (u64)chn->clk_rate * period_ns;
> > + div = NSEC_PER_SEC * SPRD_PWM_MOD_MAX;
> > + prescale = div64_u64(tmp, div) - 1;
> > + if (prescale > SPRD_PWM_PRESCALE_MSK)
> > + prescale = SPRD_PWM_PRESCALE_MSK;
>
> This isn't the inverse of .get_state(). Consider:
>
> clk_rate = 3333333
> SPRD_PWM_PRESCALE = 15
>
> then you calculate in .get_state():
>
> period = 1224000
>
> If you then call apply with this value you calulate:
>
> prescale = 14
OK. I will optimize the logics to fix this issue in next version.
> > +
> > + /*
> > + * Note: The MOD must be configured before DUTY, and the hardware can
> > + * ensure current running period is completed before changing a new
> > + * configuration to avoid mixed settings.
>
> You write "the hardware can ensure ..". Does that actually means "The
> hardware ensures that ..." or is there some additional condition? Maybe
Yes, will update the comments.
> you mean:
>
> /*
> * Writing DUTY triggers the hardware to actually apply the
> * values written to MOD and DUTY to the output. So write DUTY
> * last.
> */
Not really, our hardware's method is, when you changed a new
configuration (MOD or duty is changed) , the hardware will wait for a
while to complete current period, then change to the new period.
>
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_MOD, SPRD_PWM_MOD_MAX);
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_DUTY, duty);
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_PRESCALE, prescale);
>
> If writing DUTY triggers the hardware to sample DUTY and MOD, what about
> PRESCALE?
See above comments.
>
> > + return 0;
> > +}
> > +
> > +static int sprd_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > + struct pwm_state *state)
> > +{
> > + struct sprd_pwm_chip *spc =
> > + container_of(chip, struct sprd_pwm_chip, chip);
> > + struct sprd_pwm_chn *chn = &spc->chn[pwm->hwpwm];
> > + struct pwm_state cstate;
> > + int ret;
> > +
> > + pwm_get_state(pwm, &cstate);
>
> I don't like it when pwm drivers call pwm_get_state(). If ever
> pwm_get_state would take a lock, this would deadlock as the lock is
> probably already taken when your .apply() callback is running. Moreover
> the (expensive) calculations are not used appropriately. See below.
I do not think so, see:
static inline void pwm_get_state(const struct pwm_device *pwm, struct
pwm_state *state)
{
*state = pwm->state;
}
>
> > + if (state->enabled) {
> > + if (!cstate.enabled) {
>
> To just know the value of cstate.enabled you only need to read the
> register with the ENABLE flag. That is cheaper than calling get_state.
>
> > + /*
> > + * The clocks to PWM channel has to be enabled first
> > + * before writing to the registers.
> > + */
> > + ret = clk_bulk_prepare_enable(SPRD_PWM_NUM_CLKS,
> > + chn->clks);
> > + if (ret) {
> > + dev_err(spc->dev,
> > + "failed to enable pwm%u clocks\n",
> > + pwm->hwpwm);
> > + return ret;
> > + }
> > + }
> > +
> > + if (state->period != cstate.period ||
> > + state->duty_cycle != cstate.duty_cycle) {
>
> This is a coarse check. If state->period and cstate.period only differ
> by one calling sprd_pwm_config(spc, pwm, state->duty_cycle,
> state->period) probably results in a noop. So you're doing an expensive
> division to get an unreliable check. It would be better to calculate the
> register values from the requested state and compare the register
> values. The costs are more or less the same than calling .get_state and
> the check is reliable. And you don't need to spend another division to
> calculate the new register values.
Same as above comment.
>
> > + ret = sprd_pwm_config(spc, pwm, state->duty_cycle,
> > + state->period);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_ENABLE, 1);
> > + } else if (cstate.enabled) {
> > + sprd_pwm_write(spc, pwm->hwpwm, SPRD_PWM_ENABLE, 0);
> > +
> > + clk_bulk_disable_unprepare(SPRD_PWM_NUM_CLKS, chn->clks);
>
> Assuming writing SPRD_PWM_ENABLE = 0 to the hardware completes the
> currently running period and the write doesn't block that long: Does
> disabling the clocks interfere with completing the period?
Writing SPRD_PWM_ENABLE = 0 will stop the PWM immediately, will not
waiting for completing the currently period.
>
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static const struct pwm_ops sprd_pwm_ops = {
> > + .apply = sprd_pwm_apply,
> > + .get_state = sprd_pwm_get_state,
> > + .owner = THIS_MODULE,
> > +};
> > +
> > +static int sprd_pwm_clk_init(struct sprd_pwm_chip *spc)
> > +{
> > + struct clk *clk_pwm;
> > + int ret, i, clk_index = 0;
> > +
> > + for (i = 0; i < SPRD_PWM_NUM; i++) {
> > + struct sprd_pwm_chn *chn = &spc->chn[i];
> > + int j;
> > +
> > + for (j = 0; j < SPRD_PWM_NUM_CLKS; ++j)
> > + chn->clks[j].id = sprd_pwm_clks[clk_index++];
>
> I think this would be more understandable when written as:
>
> for (j = 0; j < SPRD_PWM_NUM_CLKS; ++j)
> chn->clks[j].id = sprd_pwm_clks[i * SPRD_PWM_NUM_CLKS + j];
>
> but I'm not sure I'm objective here.
Sure.
>
> > +
> > + ret = devm_clk_bulk_get(spc->dev, SPRD_PWM_NUM_CLKS, chn->clks);
> > + if (ret) {
> > + if (ret == -ENOENT)
> > + break;
> > +
> > + dev_err(spc->dev, "failed to get channel clocks\n");
>
> if ret == -EPROBE_DEFER you shouldn't issue an error message.
Yes.
>
> > + return ret;
> > + }
> > +
> > + clk_pwm = chn->clks[SPRD_PWM_OUTPUT_CLK].clk;
> > + chn->clk_rate = clk_get_rate(clk_pwm);
> > + }
> > +
> > + if (!i) {
> > + dev_err(spc->dev, "no available PWM channels\n");
> > + return -EINVAL;
>
> ENODEV?
Yes
>
> > + }
> > +
> > + spc->num_pwms = i;
> > +
> > + return 0;
> > +}
> > +
> > +static int sprd_pwm_probe(struct platform_device *pdev)
> > +{
> > + struct sprd_pwm_chip *spc;
> > + int ret;
> > +
> > + spc = devm_kzalloc(&pdev->dev, sizeof(*spc), GFP_KERNEL);
> > + if (!spc)
> > + return -ENOMEM;
> > +
> > + spc->base = devm_platform_ioremap_resource(pdev, 0);
> > + if (IS_ERR(spc->base))
> > + return PTR_ERR(spc->base);
> > +
> > + spc->dev = &pdev->dev;
> > + platform_set_drvdata(pdev, spc);
> > +
> > + ret = sprd_pwm_clk_init(spc);
> > + if (ret)
> > + return ret;
> > +
> > + spc->chip.dev = &pdev->dev;
> > + spc->chip.ops = &sprd_pwm_ops;
> > + spc->chip.base = -1;
> > + spc->chip.npwm = spc->num_pwms;
> > +
> > + ret = pwmchip_add(&spc->chip);
> > + if (ret)
> > + dev_err(&pdev->dev, "failed to add PWM chip\n");
> > +
> > + return ret;
> > +}
> > +
> > +static int sprd_pwm_remove(struct platform_device *pdev)
> > +{
> > + struct sprd_pwm_chip *spc = platform_get_drvdata(pdev);
> > + int ret, i;
> > +
> > + ret = pwmchip_remove(&spc->chip);
> > +
> > + for (i = 0; i < spc->num_pwms; i++) {
> > + struct sprd_pwm_chn *chn = &spc->chn[i];
> > +
> > + clk_bulk_disable_unprepare(SPRD_PWM_NUM_CLKS, chn->clks);
>
> If a PWM was still running you're effectively stopping it here, right?
> Are you sure you don't disable once more than you enabled?
Yes, you are right. I should check current enable status of the PWM channel.
Thanks for your comments.
--
Baolin Wang
Best Regards
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