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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 v3 4/4] watchdog: cadence_wdt: Support all available prescaler values
Date: Wed, 10 Jul 2019 13:39:31 -0700
Message-ID: <20190710203931.GB6330@roeck-us.net> (raw)
In-Reply-To: <66ed7888-7ab9-0600-78d5-f9f2ebd4bf01@vaisala.com>

On Wed, Jul 10, 2019 at 07:20:59PM +0000, Melin Tomas wrote:
> 
> On 7/10/19 12:07 AM, Guenter Roeck wrote:
> > Ah, we are talking about the _smallest_ timeout and about resolution.
> > But that is no reason to declare the clock invalid. Just set the minimum
> > to the actual minimum.  There is no reason to reject slow clocks entirely,
> > even if the granularity is in the multi-second range. The only caveat,
> > if granularity is more than one second, is that the set_timeout function
> > must select and report the actual timeout.
> 
> I did consider supporting slower clocks but thought that the required
> 
> additional logic was perhaps not worth it. So instead just declared
> 
> those clock frequencies invalid.
> 

Hmm ... not sure I understand. What makes it so difficult ?

Guenter

> However, if that logic is required, sure I can try to implement it.
> 
> It might take some weeks before I have time to look at it properly.
> 
> 
> Thanks,
> 
> Tomas
> 
> >
> > Thanks,
> > Guenter
> >
> >> Thanks,
> >>
> >> Tomas
> >>
> >>>> Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
> >>>> ---
> >>>>    drivers/watchdog/cadence_wdt.c | 21 +++++++++++++++------
> >>>>    1 file changed, 15 insertions(+), 6 deletions(-)
> >>>>
> >>>> diff --git a/drivers/watchdog/cadence_wdt.c b/drivers/watchdog/cadence_wdt.c
> >>>> index 0bdb275d904a..037faf557f9d 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
> >>>                                ^ Please use a tab here
> >>>
> >>>>    
> >>>>    /* Counter maximum value */
> >>>>    #define CDNS_WDT_COUNTER_MAX 0xFFF
> >>>> @@ -318,10 +319,18 @@ static int cdns_wdt_probe(struct platform_device *pdev)
> >>>>    		return ret;
> >>>>    
> >>>>    	clock_f = clk_get_rate(wdt->clk);
> >>>> -	if (clock_f == 0) {
> >>>> -		dev_err(dev, "invalid clock frequency, (f=%lu)\n", clock_f);
> >>>> +	if (clock_f < CDNS_WDT_CLK_32KHZ) {
> >>>> +		dev_err(dev,
> >>>> +			"cannot find suitable clock prescaler, (f=%lu)\n",
> >>>> +			clock_f);
> >>>>    		return -EINVAL;
> >>>> -	} else if (clock_f <= CDNS_WDT_CLK_75MHZ) {
> >>>> +	} 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 {
> >>>> -- 
> >>>> 2.17.2
> >>>>

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-09 20:09 [PATCH v3 0/4] " Melin Tomas
2019-07-09 20:09 ` [PATCH v3 1/4] watchdog: cadence_wdt: Move clock detection earlier in probe Melin Tomas
2019-07-09 20:15   ` Guenter Roeck
2019-07-09 20:09 ` [PATCH v3 2/4] watchdog: cadence_wdt: Calculate actual timeout limits Melin Tomas
2019-07-09 20:14   ` Guenter Roeck
2019-07-09 20:09 ` [PATCH v3 4/4] watchdog: cadence_wdt: Support all available prescaler values Melin Tomas
2019-07-09 20:21   ` Guenter Roeck
2019-07-09 20:49     ` Melin Tomas
2019-07-09 21:07       ` Guenter Roeck
2019-07-10 19:20         ` Melin Tomas
2019-07-10 20:39           ` Guenter Roeck [this message]
2019-07-11 20:10             ` Melin Tomas
2019-07-09 20:09 ` [PATCH v3 3/4] watchdog: cadence_wdt: Group struct member init statements Melin Tomas
2019-07-09 20:16   ` Guenter Roeck

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