From: ml.lawnick@gmx.de (Michael Lawnick)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] i2c: omap: improve duty cycle on SCL
Date: Fri, 19 Jun 2015 07:41:49 +0200 [thread overview]
Message-ID: <5583AB9D.6090805@gmx.de> (raw)
In-Reply-To: <20150618172428.GB27790@saruman.tx.rr.com>
Am 18.06.2015 um 19:24 schrieb Felipe Balbi:
> On Thu, Jun 18, 2015 at 08:39:11AM +0200, Michael Lawnick wrote:
>> Am 17.06.2015 um 17:38 schrieb Felipe Balbi:
>>> Hi,
>>>
>>> On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote:
>>>> Am 16.06.2015 um 21:17 schrieb Felipe Balbi:
>>>>> With this patch we try to be as close to 50%
>>>>> duty cycle as possible. The reason for this
>>>>> is that some devices present an erratic behavior
>>>>> with certain duty cycles.
>>>>>
>>>>> One such example is TPS65218 PMIC which fails
>>>>> to change voltages when running @ 400kHz and
>>>>> duty cycle is lower than 34%.
>>>>>
>>>>> The idea of the patch is simple:
>>>>>
>>>>> calculate desired scl_period from requested scl
>>>>> and use 50% for tLow and 50% for tHigh.
>>>> ...
>>>> Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5?
>>>>
>>>>> PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT
>>>>> MIN. MAX. MIN. MAX.
>>>>> LOW period of the SCL clock tLOW 4.7 ? 1.3 ? ?s
>>>>> HIGH period of the SCL clock tHIGH 4.0 ? 0.6 ? ?s
>>>>
>>>> Your signal is in spec (0.85 ?s high, 1,65 low).
>>>> Maybe your TPS65218 is just buggy or signals are bad?
>>>
>>> yes, tps is buggy, it's written in the commit log itself.
>>>
>>
>> So I think it is unacceptable to change the adapters code violating
>> specification because some buggy device doesn't work properly.
>
> read the other thread and you'll see that it's not violating jack
>
>> This change for your device has chance to blow up many correctly
>> working ones.
>
> How ?
>
The answer is so obvious that I'm a bit irritated.
Your patch description tells: 'and use 50% for tLow and 50% for tHigh'
For 400kHz this means 1.25 us for high and low. This clearly violates
the specification for minimum low period and will not work with any
device that relies on it.
In the other thread it is discussed that your patch does effectively not
do what you describe but this is something completely independent.
--
KR
Michael
WARNING: multiple messages have this Message-ID (diff)
From: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
To: balbi-l0cyMroinI0@public.gmane.org
Cc: wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org,
Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>,
Nishanth Menon <nm-l0cyMroinI0@public.gmane.org>,
Dave Gerlach <d-gerlach-l0cyMroinI0@public.gmane.org>,
linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Linux OMAP Mailing List
<linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux ARM Kernel Mailing List
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH] i2c: omap: improve duty cycle on SCL
Date: Fri, 19 Jun 2015 07:41:49 +0200 [thread overview]
Message-ID: <5583AB9D.6090805@gmx.de> (raw)
In-Reply-To: <20150618172428.GB27790-HgARHv6XitJaoMGHk7MhZQC/G2K4zDHf@public.gmane.org>
Am 18.06.2015 um 19:24 schrieb Felipe Balbi:
> On Thu, Jun 18, 2015 at 08:39:11AM +0200, Michael Lawnick wrote:
>> Am 17.06.2015 um 17:38 schrieb Felipe Balbi:
>>> Hi,
>>>
>>> On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote:
>>>> Am 16.06.2015 um 21:17 schrieb Felipe Balbi:
>>>>> With this patch we try to be as close to 50%
>>>>> duty cycle as possible. The reason for this
>>>>> is that some devices present an erratic behavior
>>>>> with certain duty cycles.
>>>>>
>>>>> One such example is TPS65218 PMIC which fails
>>>>> to change voltages when running @ 400kHz and
>>>>> duty cycle is lower than 34%.
>>>>>
>>>>> The idea of the patch is simple:
>>>>>
>>>>> calculate desired scl_period from requested scl
>>>>> and use 50% for tLow and 50% for tHigh.
>>>> ...
>>>> Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5?
>>>>
>>>>> PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT
>>>>> MIN. MAX. MIN. MAX.
>>>>> LOW period of the SCL clock tLOW 4.7 – 1.3 – µs
>>>>> HIGH period of the SCL clock tHIGH 4.0 – 0.6 – µs
>>>>
>>>> Your signal is in spec (0.85 µs high, 1,65 low).
>>>> Maybe your TPS65218 is just buggy or signals are bad?
>>>
>>> yes, tps is buggy, it's written in the commit log itself.
>>>
>>
>> So I think it is unacceptable to change the adapters code violating
>> specification because some buggy device doesn't work properly.
>
> read the other thread and you'll see that it's not violating jack
>
>> This change for your device has chance to blow up many correctly
>> working ones.
>
> How ?
>
The answer is so obvious that I'm a bit irritated.
Your patch description tells: 'and use 50% for tLow and 50% for tHigh'
For 400kHz this means 1.25 us for high and low. This clearly violates
the specification for minimum low period and will not work with any
device that relies on it.
In the other thread it is discussed that your patch does effectively not
do what you describe but this is something completely independent.
--
KR
Michael
next prev parent reply other threads:[~2015-06-19 5:41 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 19:17 [PATCH] i2c: omap: improve duty cycle on SCL Felipe Balbi
2015-06-16 19:17 ` Felipe Balbi
2015-06-16 19:19 ` Felipe Balbi
2015-06-16 19:19 ` Felipe Balbi
2015-06-17 11:09 ` Michael Lawnick
2015-06-17 11:09 ` Michael Lawnick
2015-06-17 15:38 ` Felipe Balbi
2015-06-17 15:38 ` Felipe Balbi
2015-06-18 6:39 ` Michael Lawnick
2015-06-18 6:39 ` Michael Lawnick
2015-06-18 17:24 ` Felipe Balbi
2015-06-18 17:24 ` Felipe Balbi
2015-06-19 5:41 ` Michael Lawnick [this message]
2015-06-19 5:41 ` Michael Lawnick
2015-06-19 15:30 ` Felipe Balbi
2015-06-19 15:30 ` Felipe Balbi
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