linux-kernel - Re: [PATCH 0/3] Ensure Low period of SCL is correct

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Date:   Mon, 4 Apr 2022 10:01:03 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     tanure@...ux.com, Kevin Hilman <khilman@...libre.com>
Cc:     Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Vyacheslav Bocharov <adeep@...ina.in>
Subject: Re: [PATCH 0/3] Ensure Low period of SCL is correct

Hi,

On 29/03/2022 00:31, Lucas Tanure wrote:
> On Mon, 28 Mar 2022, 21:37 Kevin Hilman, <khilman@...libre.com> wrote:
>>
>> Hi Lucas,
>>
>> Lucas Tanure <tanure@...ux.com> writes:
>>
>>> The default duty cycle of 33% is less than the required
>>> by the I2C specs for the LOW period of the SCL clock.
>>>
>>> So, for 100Khz or less, use 50%H/50%L duty cycle, and
>>> for the clock above 100Khz, use 40%H/60%L duty cycle.
>>> That ensures the low period of SCL is always more than
>>> the minimum required by the specs at any given frequency.
>>
>> Thanks for the fixes!
>>
>> This is going to affect all SoCs, so ould you please summarize how your
>> changes were tested, and on which SoCs & boards?
>>
>> Thanks,
>>
>> Kevin
> 
> Hi,
> 
> I only tested against the vim3 board, measured the bus with a Saleae
> logic pro 16.
> The measurements were with 100k, 400k, and a few in-between frequencies.

Thanks, it's a great addition to have !

> 
> Is that enough?

A test on GXL/GXM (VIM1 or VIM2) & GXBB (Odroid-C2) devices is lacking before we
can merge this.

If I find some time, I'll have a try, but everyone is welcome testing this serie
and report if it still works fine for them.

Vyacheslav, do you think you can test on your JetHub devices ? it would validate GXL & AXG.

Neil

> 
> Thanks
> Lucas