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Message-ID: <20191121073647.phutknyb3tzp44ye@pengutronix.de>
Date: Thu, 21 Nov 2019 08:36:47 +0100
From: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
To: Clément Péron <peron.clem@...il.com>
Cc: Thierry Reding <thierry.reding@...il.com>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Maxime Ripard <mripard@...nel.org>,
Chen-Yu Tsai <wens@...e.org>,
Philipp Zabel <pza@...gutronix.de>, linux-pwm@...r.kernel.org,
devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
Jernej Skrabec <jernej.skrabec@...l.net>, kernel@...gutronix.de
Subject: Re: [PATCH v7 5/8] pwm: sun4i: Add support to output source clock
directly
Hello Clément,
On Tue, Nov 19, 2019 at 06:53:16PM +0100, Clément Péron wrote:
> From: Jernej Skrabec <jernej.skrabec@...l.net>
>
> PWM core has an option to bypass whole logic and output unchanged source
> clock as PWM output. This is achieved by enabling bypass bit.
>
> Note that when bypass is enabled, no other setting has any meaning, not
> even enable bit.
>
> This mode of operation is needed to achieve high enough frequency to
> serve as clock source for AC200 chip which is integrated into same
> package as H6 SoC.
>
> Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> Signed-off-by: Clément Péron <peron.clem@...il.com>
> ---
> drivers/pwm/pwm-sun4i.c | 92 ++++++++++++++++++++++++++++-------------
> 1 file changed, 64 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> index ce83d479ba0e..a1d8851b18f0 100644
> --- a/drivers/pwm/pwm-sun4i.c
> +++ b/drivers/pwm/pwm-sun4i.c
> @@ -3,6 +3,10 @@
> * Driver for Allwinner sun4i Pulse Width Modulation Controller
> *
> * Copyright (C) 2014 Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> + *
> + * Limitations:
> + * - When outputing the source clock directly, the PWM logic will be bypassed
> + * and the currently running period is not guaranteed to be completed
> */
>
> #include <linux/bitops.h>
> @@ -73,6 +77,7 @@ static const u32 prescaler_table[] = {
>
> struct sun4i_pwm_data {
> bool has_prescaler_bypass;
> + bool has_direct_mod_clk_output;
> unsigned int npwm;
> };
>
> @@ -118,6 +123,20 @@ static void sun4i_pwm_get_state(struct pwm_chip *chip,
>
> val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
>
> + /*
> + * PWM chapter in H6 manual has a diagram which explains that if bypass
> + * bit is set, no other setting has any meaning. Even more, experiment
> + * proved that also enable bit is ignored in this case.
> + */
> + if ((val & BIT_CH(PWM_BYPASS, pwm->hwpwm)) &&
> + sun4i_pwm->data->has_direct_mod_clk_output) {
> + state->period = DIV_ROUND_UP_ULL(NSEC_PER_SEC, clk_rate);
> + state->duty_cycle = DIV_ROUND_UP_ULL(state->period, 2);
> + state->polarity = PWM_POLARITY_NORMAL;
> + state->enabled = true;
> + return;
> + }
> +
> if ((PWM_REG_PRESCAL(val, pwm->hwpwm) == PWM_PRESCAL_MASK) &&
> sun4i_pwm->data->has_prescaler_bypass)
> prescaler = 1;
> @@ -149,13 +168,23 @@ static void sun4i_pwm_get_state(struct pwm_chip *chip,
>
> static int sun4i_pwm_calculate(struct sun4i_pwm_chip *sun4i_pwm,
> const struct pwm_state *state,
> - u32 *dty, u32 *prd, unsigned int *prsclr)
> + u32 *dty, u32 *prd, unsigned int *prsclr,
> + bool *bypass)
> {
> u64 clk_rate, div = 0;
> unsigned int pval, prescaler = 0;
>
> clk_rate = clk_get_rate(sun4i_pwm->clk);
>
> + *bypass = state->enabled &&
> + (state->period * clk_rate >= NSEC_PER_SEC) &&
> + (state->period * clk_rate < 2 * NSEC_PER_SEC) &&
> + (state->duty_cycle * clk_rate * 2 >= NSEC_PER_SEC);
> +
> + /* Skip calculation of other parameters if we bypass them */
> + if (*bypass && sun4i_pwm->data->has_direct_mod_clk_output)
> + return 0;
> +
Hmm, so if my PWM doesn't support the bypass bit *bypass might still be
true on return of sun4i_pwm_calculate. It doesn't hurt because the value
is only used after another check of has_direct_mod_clk_output, but still
this is a bit confusing.
> if (sun4i_pwm->data->has_prescaler_bypass) {
> /* First, test without any prescaler when available */
> prescaler = PWM_PRESCAL_MASK;
> @@ -202,10 +231,11 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> {
> struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip);
> struct pwm_state cstate;
> - u32 ctrl;
> + u32 ctrl, period, duty, val;
> int ret;
> - unsigned int delay_us;
> + unsigned int delay_us, prescaler;
> unsigned long now;
> + bool bypass;
>
> pwm_get_state(pwm, &cstate);
>
> @@ -220,43 +250,48 @@ static int sun4i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> spin_lock(&sun4i_pwm->ctrl_lock);
> ctrl = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
>
> - if ((cstate.period != state->period) ||
> - (cstate.duty_cycle != state->duty_cycle)) {
> - u32 period, duty, val;
> - unsigned int prescaler;
> + ret = sun4i_pwm_calculate(sun4i_pwm, state, &duty, &period, &prescaler,
> + &bypass);
> + if (ret) {
> + dev_err(chip->dev, "period exceeds the maximum value\n");
> + spin_unlock(&sun4i_pwm->ctrl_lock);
> + if (!cstate.enabled)
> + clk_disable_unprepare(sun4i_pwm->clk);
> + return ret;
> + }
>
> - ret = sun4i_pwm_calculate(sun4i_pwm, state,
> - &duty, &period, &prescaler);
> - if (ret) {
> - dev_err(chip->dev, "period exceeds the maximum value\n");
> - spin_unlock(&sun4i_pwm->ctrl_lock);
> - if (!cstate.enabled)
> - clk_disable_unprepare(sun4i_pwm->clk);
> - return ret;
This would be a bit easier to review if this commit was split into two
patches. One that drops the check for cstate.period != state->period etc
(which otherwise is nearly empty when ignoring whitespace changes), and
a second that then adds bypass support.
> + if (sun4i_pwm->data->has_direct_mod_clk_output) {
> + if (bypass) {
> + ctrl |= BIT_CH(PWM_BYPASS, pwm->hwpwm);
> + /* We can skip apply of other parameters */
> + goto bypass_mode;
I would prefer to use goto only for error handling. Not sure if there is
a nice way to do that.
> + } else {
> + ctrl &= ~BIT_CH(PWM_BYPASS, pwm->hwpwm);
> }
> + }
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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