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

[Mika Westerberg]

On Tue, Dec 15, 2015 at 08:52:19AM -0600, Suravee Suthikulpanit wrote:
> 
> 
> On 12/15/2015 07:27 AM, Mika Westerberg wrote:
> >On Mon, Dec 14, 2015 at 06:53:25PM -0600, Suravee Suthikulanit wrote:
> >>>I'm not sure if this has been discussed earlier. But after looking at the
> >>>the acpi_apd driver, all we need is just the platform-specific input clock
> >>>frequency value used by the drivers/i2c/busses/i2c-designware-core.c:
> >>>i2c_dw_init() to calculate the values to program into the DW_IC_SS_SCL_HCNT
> >>>and DW_IC_SS_SCL_LCNT registers.
> >There is a way to pass *CNT values already from ACPI to the driver -- It
> >looks for method called FMCN (or SSCN) and retrieves the values from
> >there if found.
> 
> Right, I also noticed this afterward. By the way, are FMCN and SSCN
> documented anywhere in the ACPI spec?  I am trying to figure out how to
> update the ACPI table to add this information for the AMD Seattle (ARM64)
> platform, and I will also submit a patch to add the new HID for this driver.

No, they are Intel inventions for the Windows I2C driver.

Here is what I know about it:
  SSCN - Standard Mode CNTs
  FMCN - Fast Mode CNTs

They both return a package:

  Package() {
    HCNT,
    LCNT,
    SDA_hold_time,
  }