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From:   Chris Chiu <chiu@endlessm.com>
Date:   Tue, 15 May 2018 11:22:54 +0800
Message-ID: <CAB4CAwe6kjJ10s0KtVJrPMSC8UA+YLCiqbnkZ_-oFTKTFPTwCw@mail.gmail.com>
Subject: Re: [BUG] i2c-hid: ELAN Touchpad does not work on ASUS X580GD
To:     Jarkko Nikula <jarkko.nikula@linux.intel.com>
Cc:     Daniel Drake <drake@endlessm.com>,
        Jian-Hong Pan <jian-hong@endlessm.com>,
        Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        Jani Nikula <jani.nikula@intel.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Adrian Salido <salidoa@google.com>,
        Jason Gerecke <killertofu@gmail.com>,
        linux-input <linux-input@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Wolfram Sang <wsa@the-dreams.de>, linux-i2c@vger.kernel.org,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Linux Upstreaming Team <linux@endlessm.com>
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On Mon, May 14, 2018 at 10:20 PM, Jarkko Nikula
<jarkko.nikula@linux.intel.com> wrote:
> On 05/10/2018 03:03 PM, Chris Chiu wrote:
>>
>> Report from guys who can access scope. If i2c-sda-falling-time-ns=400ns
>> , HCNT increase to 117, the SCL high duration is 576ns as follows
>> https://pasteboard.co/HkwERvP.png
>>
>> The original SCL high duration (HCNT = 105, 120MHz) is as follows
>> https://pasteboard.co/HkwFxgY.png
>>
>> So the HCNT does affect but per this HCNT/LCNT value, just not 400kHz
>> as expected. Any suggestion?
>>
> Thanks for measurements. I was sidetracked last week so I don't have yet
> explanation why signals run faster than expected :-(
>
> Using 120 MHz SPT I2C clocks in commit b418bbff36dd ("mfd: intel-lpss: Add
> Intel Cannonlake PCI IDs") is clearly wrong but before going to 133 MHz
> (which work for you but still runs too fast) I would like to find
> explanation why it appears to be much higher.
>
> --
> Jarkko

What if I change the 120MHz to 180MHz and then make sure that the I2C operates
in target FS mode frequency 400kHz via scope? Would there be any side effect?
Maybe some other busses frequency could be also affected and causing some other
component malfunction?

Chris