linux-kernel - Re: [PATCH v10 5/6] pwm: bcm2835: Allow PWM driver to be used in atomic context

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Message-ID: <3tkfjp64hw42kzj4pex2ql6lyp7r6gm2u42nq6e3av736cinrq@ykylo7d2zs3i>
Date: Tue, 19 Dec 2023 17:58:05 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Sean Young <sean@...s.org>
Cc: linux-media@...r.kernel.org, linux-pwm@...r.kernel.org, 
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>, Thierry Reding <thierry.reding@...il.com>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, Ray Jui <rjui@...adcom.com>, 
	Scott Branden <sbranden@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, linux-rpi-kernel@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 5/6] pwm: bcm2835: Allow PWM driver to be used in
 atomic context

On Tue, Dec 19, 2023 at 04:30:28PM +0000, Sean Young wrote:
> clk_get_rate() may do a mutex lock. Fetch the clock rate once, and prevent
> rate changes using clk_rate_exclusive_get().
> 
> Signed-off-by: Sean Young <sean@...s.org>
> Reviewed-by: Florian Fainelli <florian.fainelli@...adcom.com>
> ---
>  drivers/pwm/pwm-bcm2835.c | 34 +++++++++++++++++++++++++---------
>  1 file changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
> index ab30667f4f95..d9ac50a5b04e 100644
> --- a/drivers/pwm/pwm-bcm2835.c
> +++ b/drivers/pwm/pwm-bcm2835.c
> @@ -28,6 +28,7 @@ struct bcm2835_pwm {
>  	struct device *dev;
>  	void __iomem *base;
>  	struct clk *clk;
> +	unsigned long rate;
>  };
>  
>  static inline struct bcm2835_pwm *to_bcm2835_pwm(struct pwm_chip *chip)
> @@ -63,17 +64,11 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  {
>  
>  	struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
> -	unsigned long rate = clk_get_rate(pc->clk);
>  	unsigned long long period_cycles;
>  	u64 max_period;
>  
>  	u32 val;
>  
> -	if (!rate) {
> -		dev_err(pc->dev, "failed to get clock rate\n");
> -		return -EINVAL;
> -	}
> -
>  	/*
>  	 * period_cycles must be a 32 bit value, so period * rate / NSEC_PER_SEC
>  	 * must be <= U32_MAX. As U32_MAX * NSEC_PER_SEC < U64_MAX the
> @@ -88,13 +83,13 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	 * <=> period < ((U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC/2) / rate
>  	 * <=> period <= ceil((U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC/2) / rate) - 1
>  	 */
> -	max_period = DIV_ROUND_UP_ULL((u64)U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC / 2, rate) - 1;
> +	max_period = DIV_ROUND_UP_ULL((u64)U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC / 2, pc->rate) - 1;
>  
>  	if (state->period > max_period)
>  		return -EINVAL;
>  
>  	/* set period */
> -	period_cycles = DIV_ROUND_CLOSEST_ULL(state->period * rate, NSEC_PER_SEC);
> +	period_cycles = DIV_ROUND_CLOSEST_ULL(state->period * pc->rate, NSEC_PER_SEC);
>  
>  	/* don't accept a period that is too small */
>  	if (period_cycles < PERIOD_MIN)
> @@ -103,7 +98,7 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	writel(period_cycles, pc->base + PERIOD(pwm->hwpwm));
>  
>  	/* set duty cycle */
> -	val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * rate, NSEC_PER_SEC);
> +	val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * pc->rate, NSEC_PER_SEC);
>  	writel(val, pc->base + DUTY(pwm->hwpwm));
>  
>  	/* set polarity */
> @@ -131,6 +126,13 @@ static const struct pwm_ops bcm2835_pwm_ops = {
>  	.apply = bcm2835_pwm_apply,
>  };
>  
> +static void devm_clk_rate_exclusive_put(void *data)
> +{
> +	struct clk *clk = data;
> +
> +	clk_rate_exclusive_put(clk);
> +}
> +
>  static int bcm2835_pwm_probe(struct platform_device *pdev)
>  {
>  	struct bcm2835_pwm *pc;
> @@ -151,8 +153,22 @@ static int bcm2835_pwm_probe(struct platform_device *pdev)
>  		return dev_err_probe(&pdev->dev, PTR_ERR(pc->clk),
>  				     "clock not found\n");
>  
> +	ret = clk_rate_exclusive_get(pc->clk);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret,
> +				     "fail to get exclusive rate\n");
> +
> +	devm_add_action_or_reset(&pdev->dev, devm_clk_rate_exclusive_put,
> +				 pc->clk);

Missing error checking.

Otherwise looks good now.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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