From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joe Perches <joe@perches.com>
Subject: Re: [PATCH V1 1/1] iio: Added Capella cm3232 ambient light sensor
 driver.
Date: Mon, 05 Jan 2015 09:56:51 -0800
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To: Daniel Baluta <daniel.baluta@intel.com>
Cc: Kevin Tsai <ktsai@capellamicro.com>, Wolfram Sang <wsa@the-dreams.de>, Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>, Ian Campbell <ijc+devicetree@hellion.org.uk>, Kumar Gala <galak@codeaurora.org>, Jonathan Cameron <jic23@kernel.org>, Hartmut Knaack <knaack.h@gmx.de>, Lars-Peter Clausen <lars@metafoo.de>, Peter Meerwald <pmeerw@pmeerw.net>, Grant Likely <grant.likely@linaro.org>, Andrew Morton <akpm@linux-foundation.org>, "David S. Miller" <davem@davemloft.net>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Mauro Carvalho Chehab <mchehab@osg.samsung.com>, Antti Palosaari <crope@iki.fi>, Archana Patni <archana.patni@linux.intel.com>, linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, 2015-01-05 at 19:50 +0200, Daniel Baluta wrote:
> On Mon, Jan 5, 2015 at 6:42 PM, Joe Perches <joe@perches.com> wrote:
> > On Mon, 2015-01-05 at 16:20 +0200, Daniel Baluta wrote:
> >> On Mon, Jan 5, 2015 at 3:09 PM, Joe Perches <joe@perches.com> wrote:
> >> > On Mon, 2015-01-05 at 12:51 +0200, Daniel Baluta wrote:
> >> >> On Thu, Jan 1, 2015 at 2:10 AM, Kevin Tsai <ktsai@capellamicro.com> wrote:
> >> >> > CM3232 is an advanced ambient light sensor with I2C protocol interface.
> >> >> > The I2C slave address is internally hardwired as 0x10 (7-bit).  Writing
> >> >> > to configure register is byte mode, but reading ALS register requests to
> >> >> > use word mode for 16-bit resolution.
> > []
> >> >> You could directly return i2c_smbus_write_byte_data(..).
> >> >
> >> > Sometimes it's better to return a specific value
> >> > for the error instead of depending on correctness
> >> > of all the indirect functions in the call chain.
> >> >
> >> > In this case, all the smbus_xfer functions must
> >> > return 0 on success.  Do they?
> >>
> >> Yes.
> >>
> >> http://lxr.free-electrons.com/source/drivers/i2c/i2c-core.c#L2845
> >
> > This doesn't show that adapter->algo->smbus_xfer()
> > returns 0, you have to look at the code for that
> > indirectly called function.
> 
> I based my answer on the comment at the top of the function:
> 
> 2845  * This executes an SMBus protocol operation, and returns a negative
> 2846  * errno code else zero on success.

Sure, but comments and code often differ and the
implementation of any of those smbus_xfer functions
could return a positive value like the byte value or
the number of bytes written instead of 0.

For correctness, you'd have to inspect them all.

If some new future smbus_xfer function was written
incorrectly, the return value from this function could
now be positive.

cheers, Joe