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

Uwe Kleine-König
2019-11-18T07:15:46Z

Hello Paul,

On Sun, Nov 17, 2019 at 11:58:43PM +0100, Paul Cercueil wrote:
> 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.

Before you used driver data and container_of to get it, now you used
pwm_set_chip_data. I wondered why you changed the approach to store
data. That the actual data is different now is another thing (and
obviously ok).

> > > };
> > >
> > > 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.

Yeah, that's new and IMHO quite nice.

> > > + 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.

I'd like to understand what it does. Judging from the name I expect this
is somehow related to the clock stuff and so I wonder if the conversion
to the clk API is as complete as it should be.

> > > - 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.

Then the approach here is wrong. You should not assume anything about
the internal details of the clock, that's the task of the clock driver.
As a consumer of the clock just request a rate (or use clk_round_rate to
find a good setting first) and use that.

Best regards
Uwe

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