From: Guenter Roeck <linux@roeck-us.net>
To: Jean Delvare <jdelvare@suse.de>
Cc: Robert Rosengren <robert.rosengren@axis.com>,
lm-sensors@lm-sensors.org, Johan Adolfsson <johana@axis.com>,
linux-kernel@vger.kernel.org
Subject: Re: [lm-sensors] [PATCH] hwmon: (ads7828) Make sample interval configurable
Date: Tue, 27 Jan 2015 20:06:13 -0800 [thread overview]
Message-ID: <54C86035.9080605@roeck-us.net> (raw)
In-Reply-To: <20150127233455.0c62457e@endymion.delvare>
On 01/27/2015 02:34 PM, Jean Delvare wrote:
> On Tue, 27 Jan 2015 12:05:53 -0800, Guenter Roeck wrote:
>> On Tue, Jan 27, 2015 at 08:54:34PM +0100, Robert Rosengren wrote:
>>> Guenter and Jean,
>>>
>>> To sum up, my problems was related my kernel and hardware configuration, and it now works. Many thanks for your input!
>>>
>>> However, the values retrieved from hwmon sysfs is not the same as before the regmap patch. Guenter, the byte swap for the regval retrieved by regmap_read. In what order is the bits returned from that function, because it seems as if I disabled that code I get values as I expect (i.e. before the regmap patch).
>>>
>> Trying to understand. Are you saying everything works as expected
>> if you keep byte_swap set to false ?
>>
>> That might well be, though it might mean that regmap has a bug
>> in how it treats i2c word read operations. I'll have to look into it
>> some more.
>
> Remember that SMBus specifies that the LSB comes first (and i2c-core
> implement things that way) while real I2C devices typically send the MSB
> first. This has always caused confusion. This is why a lot of drivers
> need byte-swapping.
>
regmap specifies "normal" i2c accesses as MSB first. When SMBus accesses
are used, it specifies LSB first. I guess that means that regmap assumes
the more common case of MSB first, meaning the driver would not need a byte
swap since the chip reports data with MSB first.
I just hope I interpret it correctly this time.
There is also a configuration flag "val_format_endian" which can be set to
REGMAP_ENDIAN_BIG or REGMAP_ENDIAN_LITTLE. Maybe that can be used as well
if needed. Either case I'll wait for the samples before I send an updated
version of the patch.
Guenter
next prev parent reply other threads:[~2015-01-28 4:06 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-16 12:05 [PATCH] hwmon: (ads7828) Make sample interval configurable Robert Rosengren
2015-01-16 14:52 ` Guenter Roeck
2015-01-16 18:30 ` [lm-sensors] " Guenter Roeck
2015-01-19 11:14 ` SV: " Robert Rosengren
2015-01-27 7:59 ` Robert Rosengren
2015-01-27 10:37 ` Jean Delvare
2015-01-27 14:23 ` Guenter Roeck
2015-01-27 14:07 ` Guenter Roeck
2015-01-27 19:54 ` Robert Rosengren
2015-01-27 20:05 ` Guenter Roeck
2015-01-27 22:34 ` Jean Delvare
2015-01-28 4:06 ` Guenter Roeck [this message]
[not found] ` <54C87F3C.2020105@axis.com>
2015-01-28 6:28 ` Robert Rosengren
2015-01-28 14:50 ` Guenter Roeck
2015-01-29 7:00 ` Robert Rosengren
2015-01-29 7:05 ` Guenter Roeck
2015-01-29 12:07 ` Robert Rosengren
2015-01-29 14:10 ` Guenter Roeck
2015-01-29 19:30 ` Guenter Roeck
2015-01-31 20:11 ` Guenter Roeck
2015-02-02 8:12 ` Robert Rosengren
2015-02-02 16:21 ` Guenter Roeck
2015-01-27 14:26 ` Guenter Roeck
2015-01-27 16:37 ` Guenter Roeck
2015-01-16 20:30 ` Guenter Roeck
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