linux-kernel - Re: [PATCH 1/4] rtc: mcp795: fix invalid month setting.

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Message-ID: <20161205221559.ixqsqsqnupgjtekk@piout.net>
Date:   Mon, 5 Dec 2016 23:15:59 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Emil Bartczak <emilbart@...il.com>
Cc:     a.zummo@...ertech.it, rtc-linux@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] rtc: mcp795: fix invalid month setting.

On 05/12/2016 at 23:03:52 +0100, Emil Bartczak wrote :
> > 
> > >  #define MCP795_WRITE	0x12
> > >  #define MCP795_UNLOCK	0x14
> > >  #define MCP795_IDWRITE	0x32
> > > @@ -39,6 +39,7 @@
> > >  
> > >  #define MCP795_ST_BIT	0x80
> > >  #define MCP795_24_BIT	0x40
> > > +#define MCP795_LP_BIT	0x20
> > >  
> > >  static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
> > >  {
> > > @@ -108,7 +109,8 @@ static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
> > >  	data[1] = (data[1] & 0x80) | ((tim->tm_min / 10) << 4) | (tim->tm_min % 10);
> > >  	data[2] = ((tim->tm_hour / 10) << 4) | (tim->tm_hour % 10);
> > >  	data[4] = ((tim->tm_mday / 10) << 4) | ((tim->tm_mday) % 10);
> > > -	data[5] = (data[5] & 0x10) | (tim->tm_mon / 10) | (tim->tm_mon % 10);
> > > +	data[5] = (data[5] & MCP795_LP_BIT) |
> > 
> > You changed 0x10 in MCP795_LP_BIT which you defined as 0x20, is that
> > right?
> Yes, it should be 0x20 (checked in datasheet).
> 
> > 
> > This is also an unrelated change.
> > 
> > > +			((tim->tm_mon / 10) << 4) | (tim->tm_mon % 10);
> What do you mean exactly? 
> That above line of code was moved to the new line? Or that I added
> shift left operation (tim->tm_mon / 10) << 4)?
> Changing 0x10 to 0x20 and adding shift right operation fixes the problem.
> 

I meant that I feel like changing 0x10 to 0x20 is a separate bugfix from
adding the shift. At least mention that in the commit message.

> > >  
> > >  	if (tim->tm_year > 100)
> > >  		tim->tm_year -= 100;
> > > @@ -137,11 +139,11 @@ static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
> > >  	if (ret)
> > >  		return ret;
> > >  
> > > -	tim->tm_sec		= ((data[0] & 0x70) >> 4) * 10 + (data[0] & 0x0f);
> > > -	tim->tm_min		= ((data[1] & 0x70) >> 4) * 10 + (data[1] & 0x0f);
> > > +	tim->tm_sec	= ((data[0] & 0x70) >> 4) * 10 + (data[0] & 0x0f);
> > > +	tim->tm_min	= ((data[1] & 0x70) >> 4) * 10 + (data[1] & 0x0f);
> > >  	tim->tm_hour	= ((data[2] & 0x30) >> 4) * 10 + (data[2] & 0x0f);
> > >  	tim->tm_mday	= ((data[4] & 0x30) >> 4) * 10 + (data[4] & 0x0f);
> > > -	tim->tm_mon		= ((data[5] & 0x10) >> 4) * 10 + (data[5] & 0x0f);
> > > +	tim->tm_mon	= ((data[5] & 0x10) >> 4) * 10 + (data[5] & 0x0f);
> > 
> > All those whitespace changes are actually confusing. Please do them in a
> > separate patch or in your last patch.
> Ok, I will have a separate patch for them.

Maybe switching to bcd2bin/bin2bcd first is better as it touches all
those lines anyway and also solves the shift in mcp795_rtcc_read()


-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com