linux-kernel - Re: [PATCH] rtc: pcf2127: add error message if writing to CLKOUT register fails

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Date:   Fri, 21 Jan 2022 18:06:29 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Hugo Villeneuve <hugo@...ovil.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Hugo Villeneuve <hvilleneuve@...onoff.com>,
        linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: pcf2127: add error message if writing to CLKOUT
 register fails

On 20/01/2022 18:35:48-0500, Hugo Villeneuve wrote:
> On Wed, 19 Jan 2022 20:10:20 +0100
> Alexandre Belloni <alexandre.belloni@...tlin.com> wrote:
> 
> > On 19/01/2022 13:08:45-0500, Hugo Villeneuve wrote:
> > > On Wed, 19 Jan 2022 18:37:40 +0100
> > > Alexandre Belloni <alexandre.belloni@...tlin.com> wrote:
> > > 
> > > > On 19/01/2022 12:27:39-0500, Hugo Villeneuve wrote:
> > > > > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > > > > 
> > > > > If writing to CLKOUT register fails, the probe operation will be aborted
> > > > > without a meaningful error message.
> > > > > 
> > > > 
> > > > The current trend is to remove debug messages, please do not add more :)
> > > 
> > > Hi,
> > > If the read operation fails, the probe function will exit silently, and our RTC chip will not work. In that case, if we parse the dmesg logs, I think we  should have an indication that something went wrong.
> > > 
> > 
> > This is not true, it doesn't fail silently, you'd get:
> > rtc-pcf2127: probe of 1-0051 failed with error -121
> 
> Well this is certainly true for me because I am not seing the same error message as you :)
> 
> Just for context, I have defined a dummy pcf2127 on I2C bus 0 in my device tree (no actual hardware is present). I also added some debug messages to investigate (rtc-pcf2127.c and dd.c files), and here is the dmesg log after issuing "modprobe rtc-pcf2127":
> 
> [Thu Jan 20 23:22:20 2022] rtc-pcf2127-i2c 0-0051: pcf2127_i2c_probe
> [Thu Jan 20 23:22:20 2022] rtc-pcf2127-i2c 0-0051: pcf2127_probe
> [Thu Jan 20 23:22:20 2022] rtc-pcf2127-i2c 0-0051: PORO disabling failed with error -6
> [Thu Jan 20 23:22:20 2022] rtc-pcf2127-i2c 0-0051: call_driver_probe probe error: -6
> 
> Error code -6 is -ENXIO, and looking at the call_driver_probe() function in dd.c, I now understand why I didn't see the error message (line 531):
> 
> 	case -ENXIO:
> 		pr_debug("%s: probe of %s rejects match %d\n",
> 			 drv->name, dev_name(dev), ret);
> 
> So it seems that the return code is different than what you got?
> 

Probably because we don't have the same i2c controller and the driver
for mine is returning -EREMOTEIO when the device is not present.


-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com