Messages in this thread | | | Subject | Re: [PATCH v2 1/2] rtc: pcf2127: Disable Power-On Reset Override | From | Philipp Rosenberger <> | Date | Thu, 14 Jan 2021 12:11:59 +0100 |
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On 14.01.21 11:53, Alexandre Belloni wrote: > On 14/01/2021 11:43:22+0100, Philipp Rosenberger wrote: >> On 14.01.21 10:33, Alexandre Belloni wrote: >>> Hi, >>> >>> On 14/01/2021 10:10:32+0100, Philipp Rosenberger wrote: >>>> >>>> >>>> On 14.01.21 09:05, Uwe Kleine-König wrote: >>>>> On Wed, Jan 13, 2021 at 12:27:41PM +0100, Philipp Rosenberger wrote: >>>>>> To resume normal operation after a total power loss (no or empty >>>>>> battery) the "Power-On Reset Override (PORO)" facility needs to be >>>>>> disabled. >>>>>> >>>>>> As the oscillator may take a long time (200 ms to 2 s) to resume normal >>>>>> operation. The default behaviour is to use the PORO facility. >>>>> >>>>> I'd write instead: The register reset value sets PORO enabled and the >>>>> data sheet recommends setting it to disabled for normal operation. >>>> >>>> Sounds good, I will rephrase it. >>>> >>>>> In my eyes having a reset default value that is unsuitable for >>>>> production use is just another bad design choice of this chip. At least >>>>> now this is known and can be somewhat fixed in software. :-\ >>>> >>>> Yes, had my fair share of WTF moments with this chip. >>>> >>>>>> But with the PORO active no interrupts are generated on the interrupt >>>>>> pin (INT). >>>>> >>>>> This sentence about no interrupts is your observation, or does this base >>>>> on some authoritative source (datasheet, FAE or similar)? >>>>> >>>> >>>> Yes this is only may observation. I tested this with the OM13513 demoboard >>>> with PCF2127 and pcf2129. So I should rephrase it to something like this: >>>> >>>> Some testes suggests that no interrupts are generated on the interrupt pin >>>> if the PORP is active. >>>> >>>>>> Signed-off-by: Philipp Rosenberger <p.rosenberger@kunbus.com> >>>>>> --- >>>>>> drivers/rtc/rtc-pcf2127.c | 18 ++++++++++++++++++ >>>>>> 1 file changed, 18 insertions(+) >>>>>> >>>>>> diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c >>>>>> index 39a7b5116aa4..378b1ce812d6 100644 >>>>>> --- a/drivers/rtc/rtc-pcf2127.c >>>>>> +++ b/drivers/rtc/rtc-pcf2127.c >>>>>> @@ -26,6 +26,7 @@ >>>>>> /* Control register 1 */ >>>>>> #define PCF2127_REG_CTRL1 0x00 >>>>>> +#define PCF2127_BIT_CTRL1_POR_OVRD BIT(3) >>>>>> #define PCF2127_BIT_CTRL1_TSF1 BIT(4) >>>>>> /* Control register 2 */ >>>>>> #define PCF2127_REG_CTRL2 0x01 >>>>>> @@ -612,6 +613,23 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap, >>>>>> ret = devm_rtc_nvmem_register(pcf2127->rtc, &nvmem_cfg); >>>>>> } >>>>>> + /* >>>>>> + * The "Power-On Reset Override" facility prevents the RTC to do a reset >>>>>> + * after power on. For normal operation the PORO must be disabled. >>>>>> + */ >>>>>> + regmap_clear_bits(pcf2127->regmap, PCF2127_REG_CTRL1, >>>>>> + PCF2127_BIT_CTRL1_POR_OVRD); >>>>>> + /* >>>>>> + * If the PORO can't be disabled, just move on. The RTC should >>>>>> + * work fine, but functions like watchdog and alarm interrupts might >>>>>> + * not work. There will be no interrupt generated on the interrupt pin. >>>>>> + */ >>>>>> + ret = regmap_test_bits(pcf2127->regmap, PCF2127_REG_CTRL1, PCF2127_BIT_CTRL1_POR_OVRD); >>>>>> + if (ret <= 0) { >>>>>> + dev_err(dev, "%s: can't disable PORO (ctrl1).\n", __func__); >>>>>> + dev_warn(dev, "Watchdog and alarm functions might not work properly\n"); >>>>> >>>>> I would not emit two messages here. Also including __func__ isn't so >>>>> nice IMHO. (Great for debugging, but not in production code IMHO.) >>>> >>>> Yes, I dislike the style of the messages in this module. I just thought to >>>> keep it consistent. >>> >>> No one will ever read the message, the whole test is useless. >> >> Sorry, if I bother you with may questions. I'm unsure of why do you think >> the test is useless. Is it because it is unlikely to happen? Or that it is >> not relevant to report this? > > It is not relevant because no action will be taken by the user following > this message.
I can't really agree on that. As I consider myself a user. And I spend some time on debugging the watchdog of this chip as I didn't get any error or warning. It is your subsystem, so you make the rules. But I don't like the idea of a watchdog which silently fails. But if you insist on removing this test I will do so.
Best Regards, Philipp
>> >>>> >>>> I'm thinking of rewriting this driver as MFD driver. We use the CLKOUT for >>>> some products. So maybe a RTC, watchdog and clock driver on top of an MFD. >>>> But I'm not sure if it is really a good idea. The behavior of the chip to >>>> disable the watchdog when reading ctrl2 (i think it was) giving me a >>>> headache. >>> >>> Don't, this is not an MFD. There is no issue with having the RTC driver >>> being a clock provider. >> >> OK, this is a clear statement. >> >> Best Regards, >> Philipp >
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