From: Chris Packham <Chris.Packham@alliedtelesis.co.nz>
To: Guenter Roeck <linux@roeck-us.net>,
"jdelvare@suse.com" <jdelvare@suse.com>
Cc: "linux-hwmon@vger.kernel.org" <linux-hwmon@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: Errant readings on LM81 with T2080 SoC
Date: Tue, 9 Mar 2021 23:35:07 +0000 [thread overview]
Message-ID: <b1ba3f34-cbcc-4bbd-ea84-aad21f513682@alliedtelesis.co.nz> (raw)
In-Reply-To: <96d660bc-17ab-4e0e-9a94-bce1737a8da1@roeck-us.net>
On 8/03/21 1:31 pm, Guenter Roeck wrote:
> On 3/7/21 2:52 PM, Chris Packham wrote:
>> Fundamentally I think this is a problem with the fact that the LM81 is
>> an SMBus device but the T2080 (and other Freescale SoCs) uses i2c and we
>> emulate SMBus. I suspect the errant readings are when we don't get round
>> to completing the read within the timeout specified by the SMBus
>> specification. Depending on when that happens we either fail the
>> transfer or interpret the result as all-1s.
> That is quite unlikely. Many sensor chips are SMBus chips connected to
> i2c busses. It is much more likely that there is a bug in the T2080 i2c driver,
> that the chip doesn't like the bulk read command issued through regmap, that
> the chip has problems with the i2c bus speed, or that the i2c bus is noisy.
I have noticed that with the switch to regmap we end up using plain i2c
instead of SMBUS. There appears to be no way of saying use SMBUS
semantics if the i2c adapter reports I2C_FUNC_I2C.
next prev parent reply other threads:[~2021-03-09 23:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-07 22:52 Errant readings on LM81 with T2080 SoC Chris Packham
2021-03-08 0:31 ` Guenter Roeck
2021-03-08 2:27 ` Chris Packham
2021-03-08 4:37 ` Chris Packham
2021-03-08 4:59 ` Guenter Roeck
2021-03-08 20:27 ` Chris Packham
2021-03-08 22:39 ` Guenter Roeck
2021-03-10 2:19 ` Chris Packham
2021-03-10 5:06 ` Guenter Roeck
2021-03-10 21:48 ` Chris Packham
2021-03-11 7:41 ` Guenter Roeck
2021-03-11 8:18 ` Wolfram Sang
2021-03-11 15:19 ` Guenter Roeck
2021-03-11 21:17 ` Chris Packham
2021-03-11 21:34 ` Guenter Roeck
2021-03-11 23:47 ` Chris Packham
2021-03-12 0:07 ` Guenter Roeck
2021-03-12 0:19 ` Chris Packham
2021-03-12 9:25 ` David Laight
2021-03-14 21:26 ` Chris Packham
2021-03-15 9:46 ` David Laight
2021-03-18 5:44 ` Wolfram Sang
2021-03-18 3:46 ` Chris Packham
2021-03-18 4:02 ` Guenter Roeck
2021-03-18 5:39 ` Wolfram Sang
2021-03-08 22:10 ` Chris Packham
2021-03-09 4:36 ` Chris Packham
2021-03-09 5:24 ` Guenter Roeck
2021-03-09 23:35 ` Chris Packham [this message]
2021-03-10 3:29 ` Guenter Roeck
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