Re: [PATCH v3 11/14] rtc: pcf2127: adapt time/date registers write sequence for PCF2131

[Hugo Villeneuve]

On Fri, 20 Jan 2023 18:09:41 +0100
Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> wrote:

> On 15/12/2022 10:02:12-0500, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
> > 
> > The sequence for updating the time/date registers is slightly
> > different between PCF2127/29 and PCF2131.
> > 
> > For PCF2127/29, during write operations, the time counting
> > circuits (memory locations 03h through 09h) are automatically blocked.
> > 
> > For PCF2131, time/date registers write access requires setting the
> > STOP bit and sending the clear prescaler instruction (CPR). STOP then
> > needs to be released once write operation is completed.
> > 
> > Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
> > ---
> >  drivers/rtc/rtc-pcf2127.c | 38 +++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 37 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
> > index e4b78b9c03f9..11fbdab6bf01 100644
> > --- a/drivers/rtc/rtc-pcf2127.c
> > +++ b/drivers/rtc/rtc-pcf2127.c
> > @@ -39,6 +39,7 @@
> >  #define PCF2127_REG_CTRL1		0x00
> >  #define PCF2127_BIT_CTRL1_POR_OVRD		BIT(3)
> >  #define PCF2127_BIT_CTRL1_TSF1			BIT(4)
> > +#define PCF2127_BIT_CTRL1_STOP			BIT(5)
> >  /* Control register 2 */
> >  #define PCF2127_REG_CTRL2		0x01
> >  #define PCF2127_BIT_CTRL2_AIE			BIT(1)
> > @@ -70,6 +71,7 @@
> >  #define PCF2131_REG_SR_RESET		0x05
> >  #define PCF2131_SR_RESET_READ_PATTERN	0b00100100 /* Fixed pattern. */
> >  #define PCF2131_SR_RESET_RESET_CMD	0x2C /* SR is bit 3. */
> > +#define PCF2131_SR_RESET_CPR_CMD	0xA4 /* CPR is bit 7. */
> >  /* Time and date registers */
> >  #define PCF2127_REG_TIME_DATE_BASE	0x03
> >  #define PCF2131_REG_TIME_DATE_BASE	0x07 /* Register 0x06 is 100th seconds,
> > @@ -307,7 +309,31 @@ static int pcf2127_rtc_set_time(struct device *dev, struct rtc_time *tm)
> >  	/* year */
> >  	buf[i++] = bin2bcd(tm->tm_year - 100);
> >  
> > -	/* write register's data */
> > +	/* Write access to time registers:
> > +	 * PCF2127/29: no special action required.
> > +	 * PCF2131:    requires setting the STOP bit. STOP bit needs to
> > +	 *             be cleared after time registers are updated.
> > +	 *             It is also recommended to set CPR bit, although
> > +	 *             write access will work without it.
> > +	 */
> > +	if (pcf2127->cfg->has_reset_reg) {
> 
> This should probably be tied to the actual rtc model rather than the
> presence of the reset register.
> You MUST clear CPR to be able to set the time precisely.

In fact you must actually SET the CPR bit to clear the prescaler, confusing!

I was already setting the CPR bit (clearing prescaler), so I modified the confusing comment.

The CPR bit is only present IF the reset register is also present, that is why I simply used the presence of the reset register to take the correct action. This avoids to define a new bit or matching on a device model for that functionality (adding newer models could potentially mean modifying the model match).

But if you absolutely want to match on the model, I would like to know how you would like to practically do it (maybe an example)?



> 
> > +		err = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
> > +					 PCF2127_BIT_CTRL1_STOP,
> > +					 PCF2127_BIT_CTRL1_STOP);
> > +		if (err) {
> > +			dev_err(dev, "setting STOP bit failed\n");
> 
> This really needs to be less verbose. There is nothing a user can really
> do after having seen this message. Having an error in userspace will
> anyway prompt the user to retry the operation which is the only action
> it can do.

I converted the dev_err messages to dev_dbg.

In the original driver and in the same function, there is also a dev_err to handle regmap_bulk_write() failure. Do you suggest that we also make it less verbose:

err = regmap_bulk_write(pcf2127->regmap, pcf2127->cfg->reg_time_base, buf, i);
 	if (err) {
 		dev_err(dev,

???


> > +			return err;
> > +		}
> > +
> > +		err = regmap_write(pcf2127->regmap, pcf2127->cfg->reg_reset,
> > +				   PCF2131_SR_RESET_CPR_CMD);
> > +		if (err) {
> > +			dev_err(dev, "sending CPR cmd failed\n");
> > +			return err;
> > +		}
> > +	}
> > +
> > +	/* write time register's data */
> >  	err = regmap_bulk_write(pcf2127->regmap, pcf2127->cfg->regs_td_base, buf, i);
> >  	if (err) {
> >  		dev_err(dev,
> > @@ -315,6 +341,16 @@ static int pcf2127_rtc_set_time(struct device *dev, struct rtc_time *tm)
> >  		return err;
> >  	}
> >  
> > +	if (pcf2127->cfg->has_reset_reg) {
> > +		/* Clear STOP bit (PCF2131 only) after write is completed. */
> > +		err = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
> > +					 PCF2127_BIT_CTRL1_STOP, 0);
> > +		if (err) {
> > +			dev_err(dev, "clearing STOP bit failed\n");
> > +			return err;
> > +		}
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > -- 
> > 2.30.2
> > 
> 
> -- 
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
> 


-- 
Hugo Villeneuve <hugo@xxxxxxxxxxx>