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

Loc Ho
2015-12-15T19:20:03Z

Hi,

>>
>> 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,
> }

Can we not just add an AML method that will return the operation clock
frequency that the I2C driver can use? If the method doesn't existed,
we will just bail and do nothing or assume what ever default behavior?

-Loc