From: Guenter Roeck <linux@roeck-us.net>
To: Chris Packham <Chris.Packham@alliedtelesis.co.nz>,
Wolfram Sang <wsa@kernel.org>
Cc: "jdelvare@suse.com" <jdelvare@suse.com>,
"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: Wed, 17 Mar 2021 21:02:00 -0700 [thread overview]
Message-ID: <8e516ef6-340e-a873-68a9-71a10008f32c@roeck-us.net> (raw)
In-Reply-To: <9c912424-2cc9-8753-1352-1a5c27722cd2@alliedtelesis.co.nz>
On 3/17/21 8:46 PM, Chris Packham wrote:
>
> On 12/03/21 10:34 am, Guenter Roeck wrote:
>> On 3/11/21 1:17 PM, Chris Packham wrote:
>>> On 11/03/21 9:18 pm, Wolfram Sang wrote:
>>>>> Bummer. What is really weird is that you see clock stretching under
>>>>> CPU load. Normally clock stretching is triggered by the device, not
>>>>> by the host.
>>>> One example: Some hosts need an interrupt per byte to know if they
>>>> should send ACK or NACK. If that interrupt is delayed, they stretch the
>>>> clock.
>>>>
>>> It feels like something like that is happening. Looking at the T2080
>>> Reference manual there is an interesting timing diagram (Figure 14-2 if
>>> someone feels like looking it up). It shows SCL low between the ACK for
>>> the address and the data byte. I think if we're delayed in sending the
>>> next byte we could violate Ttimeout or Tlow:mext from the SMBUS spec.
>>>
>> I think that really leaves you only two options that I can see:
>> Rework the driver to handle critical actions (such as setting TXAK,
>> and everything else that might result in clock stretching) in the
>> interrupt handler, or rework the driver to handle everything in
>> a high priority kernel thread.
> I've made some reasonable progress on making i2c-mpc more interrupt
> driven. Assuming it works out for my use-case is there an opinion on
> making interrupt support mandatory? Looking at all the in-tree dts files
> that use one of the compatible strings from i2c-mpc.c they all have
> interrupt properties so in theory nothing is using the polling mode. But
> there may be some out-of-tree boards or boards using an old dtb that
> would be affected?
>
The polling code is from pre-git times. Like 2005 and earlier.
I'd say it is about time to get rid of it. Any out-of-tree users
had more than 15 years to upstream their code, after all.
Guenter
next prev parent reply other threads:[~2021-03-18 4:02 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 [this message]
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
2021-03-10 3:29 ` Guenter Roeck
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