Re: [PATCH v2 1/3] pwm: jz4740: Use clocks from TCU driver

Paul Cercueil
2019-11-17T22:58:56Z

Hi Uwe,

Le dim., nov. 17, 2019 at 21:20, Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> a écrit :
> On Sat, Nov 16, 2019 at 06:36:11PM +0100, Paul Cercueil wrote:
>> The ingenic-timer "TCU" driver provides us with clocks, that can be
>> (un)gated, reparented or reclocked from devicetree, instead of
>> having
>> these settings hardcoded in this driver.
>>
>> While this driver is devicetree-compatible, it is never (as of now)
>> probed from devicetree, so this change does not introduce a ABI
>> problem
>> with current devicetree files.
>>
>> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>> Tested-by: Mathieu Malaterre <malat@debian.org>
>> Tested-by: Artur Rojek <contact@artur-rojek.eu>
>> ---
>>
>> Notes:
>> v2: This patch is now before the patch introducing regmap, so
>> the code
>> has changed a bit.
>>
>> drivers/pwm/Kconfig | 1 +
>> drivers/pwm/pwm-jz4740.c | 45
>> ++++++++++++++++++++++++++++------------
>> 2 files changed, 33 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> index e3a2518503ed..e998e5cb01b0 100644
>> --- a/drivers/pwm/Kconfig
>> +++ b/drivers/pwm/Kconfig
>> @@ -225,6 +225,7 @@ config PWM_IMX_TPM
>> config PWM_JZ4740
>> tristate "Ingenic JZ47xx PWM support"
>> depends on MACH_INGENIC
>> + depends on COMMON_CLK
>> help
>> Generic PWM framework driver for Ingenic JZ47xx based
>> machines.
>> diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
>> index 9d78cc21cb12..fd83644f9323 100644
>> --- a/drivers/pwm/pwm-jz4740.c
>> +++ b/drivers/pwm/pwm-jz4740.c
>> @@ -24,7 +24,6 @@
>>
>> struct jz4740_pwm_chip {
>> struct pwm_chip chip;
>> - struct clk *clk;
>
> What is the motivation to go away from this approach to store the
> clock?

It's actually not the same clock. Instead of obtaining "ext" clock from
the probe, we obtain "timerX" clocks (X being the PWM channel) from the
request callback.

>> };
>>
>> static inline struct jz4740_pwm_chip *to_jz4740(struct pwm_chip
>> *chip)
>> @@ -34,6 +33,11 @@ static inline struct jz4740_pwm_chip
>> *to_jz4740(struct pwm_chip *chip)
>>
>> static int jz4740_pwm_request(struct pwm_chip *chip, struct
>> pwm_device *pwm)
>> {
>> + struct jz4740_pwm_chip *jz = to_jz4740(chip);
>> + struct clk *clk;
>> + char clk_name[16];
>> + int ret;
>> +
>> /*
>> * Timers 0 and 1 are used for system tasks, so they are
>> unavailable
>> * for use as PWMs.
>> @@ -41,16 +45,31 @@ static int jz4740_pwm_request(struct pwm_chip
>> *chip, struct pwm_device *pwm)
>> if (pwm->hwpwm < 2)
>> return -EBUSY;
>>
>> - jz4740_timer_start(pwm->hwpwm);
>> + snprintf(clk_name, sizeof(clk_name), "timer%u", pwm->hwpwm);
>> +
>> + clk = clk_get(chip->dev, clk_name);
>> + if (IS_ERR(clk))
>
> if (PTR_ERR(clk) != -EPROBE_DEFER)
> dev_err(chip->dev, "Failed to get clock: %pe\n", clk);

Never heard about that %pe. Will do that.

>
>> + return PTR_ERR(clk);
>> +
>> + ret = clk_prepare_enable(clk);
>> + if (ret) {
>> + clk_put(clk);
>> + return ret;
>> + }
>> +
>> + pwm_set_chip_data(pwm, clk);
>>
>> return 0;
>> }
>>
>> static void jz4740_pwm_free(struct pwm_chip *chip, struct
>> pwm_device *pwm)
>> {
>> + struct clk *clk = pwm_get_chip_data(pwm);
>> +
>> jz4740_timer_set_ctrl(pwm->hwpwm, 0);
>
> What is the purpose of this call? I would have expected that all these
> would go away when converting to the clk stuff?!

Some go away in patch [1/3] as they are clock-related, this one will go
away in patch [2/3] when the driver is converted to use regmap.

>
>> - jz4740_timer_stop(pwm->hwpwm);
>> + clk_disable_unprepare(clk);
>> + clk_put(clk);
>> }
>>
>> static int jz4740_pwm_enable(struct pwm_chip *chip, struct
>> pwm_device *pwm)
>> @@ -91,17 +110,21 @@ static int jz4740_pwm_apply(struct pwm_chip
>> *chip, struct pwm_device *pwm,
>> const struct pwm_state *state)
>> {
>> struct jz4740_pwm_chip *jz4740 = to_jz4740(pwm->chip);
>> + struct clk *clk = pwm_get_chip_data(pwm),
>> + *parent_clk = clk_get_parent(clk);
>> + unsigned long rate, period, duty;
>> unsigned long long tmp;
>> - unsigned long period, duty;
>> unsigned int prescaler = 0;
>> uint16_t ctrl;
>>
>> - tmp = (unsigned long long)clk_get_rate(jz4740->clk) *
>> state->period;
>> + rate = clk_get_rate(parent_clk);
>
> Why is it the parent's rate that is relevant here?

We calculate the divider to be used for the "timerX" clock, so we need
to know the parent clock.

>> + tmp = (unsigned long long)rate * state->period;
>> do_div(tmp, 1000000000);
>> period = tmp;
>>
>> while (period > 0xffff && prescaler < 6) {
>> period >>= 2;
>> + rate >>= 2;
>> ++prescaler;
>> }
>>
>> @@ -117,14 +140,14 @@ static int jz4740_pwm_apply(struct pwm_chip
>> *chip, struct pwm_device *pwm,
>>
>> jz4740_pwm_disable(chip, pwm);
>>
>> + clk_set_rate(clk, rate);
>
> This function's return code must be checked.

In practice this will never fail, but OK, will do.

Cheers,
-Paul

>
>> jz4740_timer_set_count(pwm->hwpwm, 0);
>> jz4740_timer_set_duty(pwm->hwpwm, duty);
>> jz4740_timer_set_period(pwm->hwpwm, period);
>>
>> - ctrl = JZ_TIMER_CTRL_PRESCALER(prescaler) | JZ_TIMER_CTRL_SRC_EXT
>> |
>> - JZ_TIMER_CTRL_PWM_ABBRUPT_SHUTDOWN;
>> -
>> - jz4740_timer_set_ctrl(pwm->hwpwm, ctrl);
>> + ctrl = jz4740_timer_get_ctrl(pwm->hwpwm);
>> + ctrl |= JZ_TIMER_CTRL_PWM_ABBRUPT_SHUTDOWN;
>>
>> switch (state->polarity) {
>> case PWM_POLARITY_NORMAL:
>
> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König
> |
> Industrial Linux Solutions |
> https://www.pengutronix.de/ |