Re: [PATCH] arm64: dts: rockchip: Fix i2c6 clock-frequency on NanoPC-T6

["Diederik de Haas" <diederik@cknow-tech.com>]

On Sat Sep 12, 2026 at 2:41 PM CEST, Heiko Stuebner wrote:
> Am Freitag, 11. September 2026, 17:28:33 Mitteleuropäische Sommerzeit schrieb Diederik de Haas:
>> The i2c6 bus needs to run at 200kHz, because at the default frequency of
>> 100kHz it may fail to find the RTC resulting in warnings/errors like
>> 
>>   rtc-hym8563 6-0051: no valid clock/calendar values available
>>   rtc-hym8563 6-0051: hctosys: unable to read the hardware clock
>> 
>> But only sometimes. This should not happen when there is a battery backing
>> the RTC, yet it does ... sometimes.
>
> I'm confused, shouldn't a slower clock always work?
> Like I understand how a clock that is too fast can cause issues due
> to hardware limitations, but running the bus slower somehow shouldn't
> cause issues?

Impeccable timing ... as I was just about to retract this patch.

In all my testing I regularly got those error/warning on 100kHz and not
once with 200kHz ... until just now.
My reasoning was that it was too slow to respond making the system/driver
think it wasn't there and thus causing those error/warning.

In the downstream kernel it is set to 200kHz and in my testing the downstream
image (with that kernel), I have not once seen those error/warning.
So I figured that the 100kHz was the problem.

But that's all null and void as I now did get the error/warning with 200kHz.

So please ignore/drop this and sorry for the noise.

Diederik