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From: Guenter Roeck <linux@roeck-us.net>
To: Melin Tomas <tomas.melin@vaisala.com>
Cc: "wim@linux-watchdog.org" <wim@linux-watchdog.org>,
	"linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>
Subject: Re: [PATCH v2 4/4] watchdog: cadence_wdt: Support all available prescaler values
Date: Mon, 8 Jul 2019 11:14:12 -0700
Message-ID: <20190708181412.GA14802@roeck-us.net> (raw)
In-Reply-To: <20190705114522.42565-5-tomas.melin@vaisala.com>

On Fri, Jul 05, 2019 at 11:46:04AM +0000, Melin Tomas wrote:
> Cadence watchdog HW supports prescaler values of
> 8, 64, 512 and 4096.
> 
> Add support to select prescaler values of 8 and 64 for lower
> input clock frequencies.
> 
> Prescaler value is selected to keep timeout resolution of 1 second.
> For clock frequencies below 32kHz, 1 second resolution does
> no longer hold, thereby returning an error.
> 
> Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
> ---
>  drivers/watchdog/cadence_wdt.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/watchdog/cadence_wdt.c b/drivers/watchdog/cadence_wdt.c
> index 4657800d9d8e..39109b5721c1 100644
> --- a/drivers/watchdog/cadence_wdt.c
> +++ b/drivers/watchdog/cadence_wdt.c
> @@ -33,16 +33,17 @@
>  #define CDNS_WDT_COUNTER_VALUE_DIVISOR 0x1000
>  
>  /* Clock prescaler value and selection */
> +#define CDNS_WDT_PRESCALE_8	8
>  #define CDNS_WDT_PRESCALE_64	64
>  #define CDNS_WDT_PRESCALE_512	512
>  #define CDNS_WDT_PRESCALE_4096	4096
> +#define CDNS_WDT_PRESCALE_SELECT_8	0
>  #define CDNS_WDT_PRESCALE_SELECT_64	1
>  #define CDNS_WDT_PRESCALE_SELECT_512	2
>  #define CDNS_WDT_PRESCALE_SELECT_4096	3
>  
> -/* Input clock frequency */
> -#define CDNS_WDT_CLK_10MHZ	10000000
> -#define CDNS_WDT_CLK_75MHZ	75000000
> +/* Base input clock frequency */
> +#define CDNS_WDT_CLK_32KHZ 32768
>  
>  /* Counter maximum value */
>  #define CDNS_WDT_COUNTER_MAX 0xFFF
> @@ -304,7 +305,16 @@ static int cdns_wdt_probe(struct platform_device *pdev)
>  	}
>  
>  	clock_f = clk_get_rate(wdt->clk);
> -	if (clock_f <= CDNS_WDT_CLK_75MHZ) {
> +	if (clock_f < CDNS_WDT_CLK_32KHZ) {
> +		dev_err(&pdev->dev, "cannot find suitable clock prescaler\n");
> +		return -ERANGE;

	/* Math result not representable */

is a bit misleading here. I understand there isn't a good option,
but using math errors isn't it. Just use -EINVAL if you don't have
a better idea. It might also make sense to display the returned
clock frequency.

> +	} else if (clock_f <= CDNS_WDT_CLK_32KHZ * CDNS_WDT_PRESCALE_8) {
> +		wdt->prescaler = CDNS_WDT_PRESCALE_8;
> +		wdt->ctrl_clksel = CDNS_WDT_PRESCALE_SELECT_8;
> +	} else if (clock_f <= CDNS_WDT_CLK_32KHZ * CDNS_WDT_PRESCALE_64) {
> +		wdt->prescaler = CDNS_WDT_PRESCALE_64;
> +		wdt->ctrl_clksel = CDNS_WDT_PRESCALE_SELECT_64;
> +	} else if (clock_f <= CDNS_WDT_CLK_32KHZ * CDNS_WDT_PRESCALE_512) {
>  		wdt->prescaler = CDNS_WDT_PRESCALE_512;
>  		wdt->ctrl_clksel = CDNS_WDT_PRESCALE_SELECT_512;
>  	} else {

      reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-05 11:46 [PATCH v2 0/4] " Melin Tomas
2019-07-05 11:46 ` [PATCH v2 1/4] watchdog: cadence_wdt: Move clock detection eariler in probe Melin Tomas
2019-07-08 18:03   ` Guenter Roeck
2019-07-05 11:46 ` [PATCH v2 2/4] watchdog: cadence_wdt: Calculate actual timeout limits Melin Tomas
2019-07-08 18:06   ` Guenter Roeck
2019-07-05 11:46 ` [PATCH v2 3/4] watchdog: cadence_wdt: Group struct member init statements Melin Tomas
2019-07-08 18:09   ` Guenter Roeck
2019-07-05 11:46 ` [PATCH v2 4/4] watchdog: cadence_wdt: Support all available prescaler values Melin Tomas
2019-07-08 18:14   ` Guenter Roeck [this message]

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