linux-kernel - RE: [PATCH] iio: max5487: Add support for Maxim digital potentiometers

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Message-ID: <6b5caa6c47c34d5eaa302dccf8dd89aa@EMAIL.axentia.se>
Date:	Fri, 25 Mar 2016 10:20:34 +0000
From:	Peter Rosin <peda@...ntia.se>
To:	Cristina Moraru <cristina.moraru09@...il.com>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"knaack.h@....de" <knaack.h@....de>,
	"lars@...afoo.de" <lars@...afoo.de>,
	"pmeerw@...erw.net" <pmeerw@...erw.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"daniel.baluta@...el.com" <daniel.baluta@...el.com>,
	"octavian.purdila@...el.com" <octavian.purdila@...el.com>
Subject: RE: [PATCH] iio: max5487: Add support for Maxim digital
 potentiometers

Hi again,

Cristina Moraru wrote:
> Add implementation for Maxim MAX5487, MAX5488, MAX5489
> digital potentiometers.
> 
> Signed-off-by: Cristina Moraru <cristina.moraru09@...il.com>
> CC: Daniel Baluta <daniel.baluta@...el.com>

Some more comments, the mcp4531 chips have n**2 + 1 positions,
therefore .max_pos in that driver isn't the number of wiper positions, it's
the actual maximum value. So, in this driver, the corrent number for
.max_pos would be 255, otherwise the reported scale is wrong (and then
you also need to adjust the EINVAL check in max5487_write_raw to use >
instead of >=).

Further comparison with the mcp4531 driver reveals that this driver does
not support IIO_CHAN_INFO_RAW in max5487_read_raw. I assume the SPI
interface does not support reading back the current value?

Cheers,
Peter