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Mon, 08 Jul 2019 11:14:13 -0700 (PDT) Date: Mon, 8 Jul 2019 11:14:12 -0700 From: Guenter Roeck To: Melin Tomas Cc: "wim@linux-watchdog.org" , "linux-watchdog@vger.kernel.org" Subject: Re: [PATCH v2 4/4] watchdog: cadence_wdt: Support all available prescaler values Message-ID: <20190708181412.GA14802@roeck-us.net> References: <20190705114522.42565-1-tomas.melin@vaisala.com> <20190705114522.42565-5-tomas.melin@vaisala.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190705114522.42565-5-tomas.melin@vaisala.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org 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 > --- > 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 {