From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH v2 0/2] i2c:dw: Add APM X-Gene ACPI I2C device support
Date: Wed, 23 Dec 2015 11:52:37 +0200
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To: Ken Xue <ken.xue@amd.com>
Cc: wsa@the-dreams.de, Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>, Loc Ho <lho@apm.com>, rjw@rjwysocki.net, lenb@kernel.org, linux-i2c@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, jcm@redhat.com, patches@apm.com, "Hurwitz, Sherry" <sherry.hurwitz@amd.com>, "Duran, Leo" <leo.duran@amd.com>, Hanjun Guo <hanjun.guo@linaro.org>, Al Stone <al.stone@linaro.org>, Ivan.Zheng@amd.com, Xiangliang.Yu@amd.com
List-Id: linux-acpi@vger.kernel.org

On Wed, Dec 23, 2015 at 05:34:01PM +0800, Ken Xue wrote:
> 1) Regarding
> https://msdn.microsoft.com/en-us/library/windows/hardware/dn919852(v=vs.85).aspx
> , Window I2C driver should pass MITT test. There are 5 I2C devices
> connect to one I2C bus for test. And those devices defined different
> "ConnectionSpeed" over the I2C bus by ACPI resource "I2CSerialBus".
> 
> During test, I2C bus should run in different "ConnectionSpeed" of
> device.
> 
> That means windows driver can modify I2C bus speed to match the
> "ConnectionSpeed" of device on-the-fly. Static value from SSCN and FMCN
> can not work for WITT test cases.

That is why there are *CNT methods for all supported I2C modes:

  - SSCN() - returns for standard mode (100kHz)
  - FMCN() - returns for fast mode (400kHz)
  - FPCN() - returns for fast mode+ (1MHz)
 
for High-speed mode I'm not sure what the method name is ;-)

Then the Windows driver switches between those based on what the
ConnectionSpeed is in the ACPI I2C connector.