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@xxxxxxxxxxx>
> ---
> 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 {
