Re: [PATCH v3 4/4] watchdog: cadence_wdt: Support all available prescaler values

[Melin Tomas <tomas.melin@vaisala.com>]

On 7/10/19 11:39 PM, Guenter Roeck wrote:

> 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 ?

Not necessarily difficult, just additional logic for

the set_timeout caveat.


Thanks,

Tomas



>
> 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
>>>>>>