linux-kernel - Re: [PATCH v3 10/14] rtc: pcf2127: read and validate PCF2131 device signature

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Message-Id: <20230123123118.39f5a5aab207f5942972b061@hugovil.com>
Date:   Mon, 23 Jan 2023 12:31:18 -0500
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     a.zummo@...ertech.it, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-rtc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: Re: [PATCH v3 10/14] rtc: pcf2127: read and validate PCF2131 device
 signature

On Fri, 20 Jan 2023 18:01:35 +0100
Alexandre Belloni <alexandre.belloni@...tlin.com> wrote:

> On 15/12/2022 10:02:11-0500, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > 
> > Make sure the device we are probing is really the device we are
> > interested in.
> > 
> > Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > ---
> >  drivers/rtc/rtc-pcf2127.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/drivers/rtc/rtc-pcf2127.c b/drivers/rtc/rtc-pcf2127.c
> > index 241189ee4a05..e4b78b9c03f9 100644
> > --- a/drivers/rtc/rtc-pcf2127.c
> > +++ b/drivers/rtc/rtc-pcf2127.c
> > @@ -193,11 +193,13 @@ struct pcf21xx_config {
> >  	unsigned int has_nvmem:1;
> >  	unsigned int has_bit_wd_ctl_cd0:1;
> >  	unsigned int has_int_a_b:1; /* PCF2131 supports two interrupt outputs. */
> > +	unsigned int has_reset_reg:1; /* If variant has a reset register. */
> >  	u8 regs_td_base; /* Time/data base registers. */
> >  	u8 regs_alarm_base; /* Alarm function base registers. */
> >  	u8 reg_wd_ctl; /* Watchdog control register. */
> >  	u8 reg_wd_val; /* Watchdog value register. */
> >  	u8 reg_clkout; /* Clkout register. */
> > +	u8 reg_reset;  /* Reset register if available. */
> >  	unsigned int ts_count;
> >  	struct pcf21xx_ts_config ts[4];
> >  	struct attribute_group attribute_group;
> > @@ -882,6 +884,7 @@ static struct pcf21xx_config pcf21xx_cfg[] = {
> >  		.has_nvmem = 1,
> >  		.has_bit_wd_ctl_cd0 = 1,
> >  		.has_int_a_b = 0,
> > +		.has_reset_reg = 0,
> >  		.regs_td_base = PCF2127_REG_TIME_DATE_BASE,
> >  		.regs_alarm_base = PCF2127_REG_ALARM_BASE,
> >  		.reg_wd_ctl = PCF2127_REG_WD_CTL,
> > @@ -906,6 +909,7 @@ static struct pcf21xx_config pcf21xx_cfg[] = {
> >  		.has_nvmem = 0,
> >  		.has_bit_wd_ctl_cd0 = 0,
> >  		.has_int_a_b = 0,
> > +		.has_reset_reg = 0,
> >  		.regs_td_base = PCF2127_REG_TIME_DATE_BASE,
> >  		.regs_alarm_base = PCF2127_REG_ALARM_BASE,
> >  		.reg_wd_ctl = PCF2127_REG_WD_CTL,
> > @@ -930,11 +934,13 @@ static struct pcf21xx_config pcf21xx_cfg[] = {
> >  		.has_nvmem = 0,
> >  		.has_bit_wd_ctl_cd0 = 0,
> >  		.has_int_a_b = 1,
> > +		.has_reset_reg = 1,
> >  		.regs_td_base = PCF2131_REG_TIME_DATE_BASE,
> >  		.regs_alarm_base = PCF2131_REG_ALARM_BASE,
> >  		.reg_wd_ctl = PCF2131_REG_WD_CTL,
> >  		.reg_wd_val = PCF2131_REG_WD_VAL,
> >  		.reg_clkout = PCF2131_REG_CLKOUT,
> > +		.reg_reset  = PCF2131_REG_SR_RESET,
> >  		.ts_count = 4,
> >  		.ts[0] = {
> >  			.regs_base = PCF2131_REG_TS1_BASE,
> > @@ -1075,6 +1081,20 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
> >  	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, pcf2127->rtc->features);
> >  	clear_bit(RTC_FEATURE_ALARM, pcf2127->rtc->features);
> >  
> > +	/* Read device signature if available. */
> > +	if (pcf2127->cfg->has_reset_reg) {
> > +		ret = regmap_read(pcf2127->regmap, pcf2127->cfg->reg_reset, &val);
> > +		if (ret < 0) {
> > +			dev_err(dev, "reading RESET register failed\n");
> 
> This is too verbose, please cut down on the number of strings you are
> adding.

See comment below.

> 
> > +			return ret;
> > +		}
> > +
> > +		if (val != PCF2131_SR_RESET_READ_PATTERN) {
> > +			dev_err(dev, "invalid device signature: $%02X\n", (u8)val);
> 
> I'm also not convinced this is actually useful. This may have to be
> updated for the next rtc the driver will support and what if this
> contradicts what the device tree is claiming at this address?

I will drop that section.


> > +			return -ENODEV;
> > +		}
> > +	}
> > +
> >  	if (alarm_irq > 0) {
> >  		unsigned long flags;
> >  
> > -- 
> > 2.30.2
> > 
> 
> -- 
> Alexandre Belloni, co-owner and COO, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
> 


-- 
Hugo Villeneuve <hugo@...ovil.com>