Re: [PATCH 3/3] pwm: atmel: replace loop in prescale calculation by ad-hoc calculation

From: <Claudiu.Beznea@microchip.com>
To: <uwe@kleine-koenig.org>, <thierry.reding@gmail.com>
Cc: linux-pwm@vger.kernel.org, alexandre.belloni@bootlin.com,
	Ludovic.Desroches@microchip.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 3/3] pwm: atmel: replace loop in prescale calculation by ad-hoc calculation
Date: Mon, 19 Aug 2019 09:27:49 +0000	[thread overview]
Message-ID: <6bc48dde-e6ff-c2c5-1fd0-11a10862eb7a@microchip.com> (raw)
In-Reply-To: <20190815214133.11134-3-uwe@kleine-koenig.org>

On 16.08.2019 00:41, Uwe Kleine-König wrote:
> External E-Mail
> 
> 
> The calculated values are the same with the modified algorithm. The only
> difference is that the calculation is a bit more efficient.
> 
> Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>

Acked-by: Claudiu Beznea <claudiu.beznea@microchip.com>

Tested on SAMA5D2_Xplained.

> ---
>  drivers/pwm/pwm-atmel.c | 24 +++++++++++++++++-------
>  1 file changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index d7a6d32b5774..42fe7bc043a8 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -60,7 +60,7 @@ struct atmel_pwm_registers {
>  };
>  
>  struct atmel_pwm_config {
> -	u32 max_period;
> +	u32 period_bits;
>  };
>  
>  struct atmel_pwm_data {
> @@ -119,17 +119,27 @@ static int atmel_pwm_calculate_cprd_and_pres(struct pwm_chip *chip,
>  {
>  	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
>  	unsigned long long cycles = state->period;
> +	int shift;
>  
>  	/* Calculate the period cycles and prescale value */
>  	cycles *= clk_get_rate(atmel_pwm->clk);
>  	do_div(cycles, NSEC_PER_SEC);
>  
> -	for (*pres = 0; cycles > atmel_pwm->data->cfg.max_period; cycles >>= 1)
> -		(*pres)++;
> +	/*
> +	 * The register for the period length is cfg.period_bits bits wide.
> +	 * So for each bit the number of clock cycles is wider divide the input
> +	 * clock frequency by two using pres and shift cprd accordingly.
> +	 */
> +	shift = fls(cycles) - atmel_pwm->data->cfg.period_bits;
>  
> -	if (*pres > PWM_MAX_PRES) {
> +	if (shift > PWM_MAX_PRES) {
>  		dev_err(chip->dev, "pres exceeds the maximum value\n");
>  		return -EINVAL;
> +	} else if (shift > 0) {
> +		*pres = shift;
> +		cycles >>= *pres;
> +	} else {
> +		*pres = 0;
>  	}
>  
>  	*cprd = cycles;
> @@ -289,7 +299,7 @@ static const struct atmel_pwm_data atmel_sam9rl_pwm_data = {
>  	},
>  	.cfg = {
>  		/* 16 bits to keep period and duty. */
> -		.max_period	= 0xffff,
> +		.period_bits	= 16,
>  	},
>  };
>  
> @@ -302,7 +312,7 @@ static const struct atmel_pwm_data atmel_sama5_pwm_data = {
>  	},
>  	.cfg = {
>  		/* 16 bits to keep period and duty. */
> -		.max_period	= 0xffff,
> +		.period_bits	= 16,
>  	},
>  };
>  
> @@ -315,7 +325,7 @@ static const struct atmel_pwm_data mchp_sam9x60_pwm_data = {
>  	},
>  	.cfg = {
>  		/* 32 bits to keep period and duty. */
> -		.max_period	= 0xffffffff,
> +		.period_bits	= 32,
>  	},
>  };
>  
> 
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