[PATCH v2 0/2] i2c:dw: Add APM X-Gene ACPI I2C device support

[Mika Westerberg]

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.