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

Suravee Suthikulpanit
2015-12-15T14:52:19Z

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.

> The driver could be modified not to require clock if it already knows
> *CNT values.
>

Sounds good.

Thanks,
Suravee