linux-kernel - Re: [PATCH 2/2] iio: accel: kxcjk-1013: optimize i2c transfers in trigger handler

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Message-ID: <1424446063.2916.17.camel@spandruv-mobl2>
Date:	Fri, 20 Feb 2015 15:27:43 +0000
From:	"Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:	"pmeerw@...erw.net" <pmeerw@...erw.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"Tirdea, Irina" <irina.tirdea@...el.com>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"Reus, Adriana" <adriana.reus@...el.com>
Subject: Re: [PATCH 2/2] iio: accel: kxcjk-1013: optimize i2c transfers in
 trigger handler

On Fri, 2015-02-20 at 16:23 +0100, Peter Meerwald wrote:
> > > > > +
> > > > > +		values[i] = data & 0xFF;
> > > > > +		values[i+1] = data >> 8;
> > > > 
> > > > this is incorrect; it forces the data to be little endian, however, the
> > > > endianness (as specified in the driver's .scan_type) is IIO_CPU -- the
> > > > code breaks for big-endian CPUs
> > > > 
> > > > since _read_i2c_block_data() can't do endianness conversion (and the chip
> > > > does i2c endianness, i.e. little-endian), the .scan_type should become
> > > > IIO_LE and above code is correct again but still ugly :)
> > > > 
> > > > bottom line: change .scan_type to IIO_LE
> > > > 
> > > Good point. Changing the endianess to IIO_LE is correct for either kxcjk1013_read_block_data or i2c_smbus_read_i2c_block_data.
> > > Will fix this in the next version. Thanks for catching this!
> > > 
> > I don't think changing to IIO_LE is good idea as when i2c_read_bock..
> > then the scan type will be CPU. So better to fix endianness in this
> > function.
> 
> the chip has little-endian data registers; i2c_read_block() just transfers 
> the data (no endianness conversion), so the data will still be 
> little-endian
You are right.
> 
> p.
>