linux-kernel - Re: [PATCH] I2C: busses: Do not print error message in syslog if no ACK received

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Date:	Wed, 13 Nov 2013 20:24:06 +0100
From:	Marek Vasut <marex@...x.de>
To:	Andreas Werner <wernerandy@....de>
Cc:	wsa@...-dreams.de, jacmet@...site.dk, baohua.song@....com,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] I2C: busses: Do not print error message in syslog if no ACK received

Dear Andreas Werner,

> On Tue, Nov 12, 2013 at 07:33:40PM +0100, Marek Vasut wrote:
> > Dear Andreas Werner,
> > 
> > > On Tue, Nov 12, 2013 at 07:00:59PM +0100, Marek Vasut wrote:
> > > > Dear Andreas Werner,
> > > > 
> > > > > Using the i2c-eg20t driver and call i2cdetect or probe on the bus,
> > > > > the driver will print a lot of error messages if there was no ACK
> > > > > received.
> > > > > 
> > > > > i2cdetect normally print a table with all the available devices. If
> > > > > there is no device on the address, the table will be empty.
> > > > > Currently with the i2c-eg20t driver, the table is not visible
> > > > > because the error messages destroy the table.
> > > > > 
> > > > > Error message: pch_i2c_getack return -71
> > > > > 
> > > > > This patch prevent the driver to print the messages to syslog if
> > > > > debug is not set.
> > > > > 
> > > > > Tested on Intel Atom E6xx and Eg20t Chipset.
> > > > > 
> > > > > Signed-off-by: Andreas Werner <wernerandy@....de>
> > > > > ---
> > > > > 
> > > > >  drivers/i2c/busses/i2c-eg20t.c | 2 +-
> > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/i2c/busses/i2c-eg20t.c
> > > > > b/drivers/i2c/busses/i2c-eg20t.c index 0f37529..b10c651 100644
> > > > > --- a/drivers/i2c/busses/i2c-eg20t.c
> > > > > +++ b/drivers/i2c/busses/i2c-eg20t.c
> > > > > @@ -322,7 +322,7 @@ static s32 pch_i2c_getack(struct
> > > > > i2c_algo_pch_data *adap) reg_val = ioread32(p + PCH_I2CSR) &
> > > > > PCH_GETACK;
> > > > > 
> > > > >  	if (reg_val != 0) {
> > > > > 
> > > > > -		pch_err(adap, "return%d\n", -EPROTO);
> > > > > +		pch_dbg(adap, "return%d\n", -EPROTO);
> > > > > 
> > > > >  		return -EPROTO;
> > > > >  	
> > > > >  	}
> > > > 
> > > > I'd just kill the pch_err() line altogether:
> > >   But why? I think there a few pch_err message which are interesting to
> > > 
> > > have in syslog, without building the dbg driver.
> > 
> > See below for explanation why this one particular pch_err() line can go.
> > Sorry if I was not clear enough, I meant only this one particular
> > pch_err() line, NOT all of them.
> > 
> > > > if (reg_val)
> > > > 
> > > > 	return -EPROTO;
> > > > 
> > > > That is because if you look at the only caller of this function,
> > > > which is pch_i2c_wait_for_check_xfer(), you will see that at the
> > > > only place where pch_i2c_getack() is called there is already
> > > > pch_dbg():
> > > > 
> > > > 369         if (pch_i2c_getack(adap)) {
> > > > 370                 pch_dbg(adap, "Receive NACK for slave address"
> > > > 371                         "setting\n");
> > > > 372                 return -EIO;
> > > > 373         }
> 
> Sorry i misunderstood that. You are absolutly right, thats the best
> solution for that. Remove the pch_err at getack so that only the pch_dbg
> get printed where getack is called. This should be enough information.

No problem ;-)
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