Re: CLK_OF_DECLARE advice required

[Stefan Wahren]

Am 31.05.2017 um 17:27 schrieb Stephen Warren:
> On 05/30/2017 06:23 AM, Phil Elwell wrote:
>> Hi,
>>
>> I've run into a problem using the fixed-factor clock on Raspberry Pi
>> and I'd
>> like some advice before I submit a patch.
>>
>> Some context: the aim is to use a standard UART and some external
>> circuitry
>> as a MIDI interface. This would be straightforward except that Linux
>> doesn't
>> recognise the required 31.25KHz as a valid UART baud rate. Rhe
>> workaround is
>> to declare the UART clock such that the reported rate differs from
>> the actual
>> rate. If one sets the reported rate to be (actual*38400)/31250 then
>> requesting a 38400 baud rate will result in an actual 31250 baud signal.
>
> This sounds like the wrong approach. Forcing the port to use a
> different clock rate than the user requests would prevent anyone from
> using that port for its standard purpose; it'd turn what should be a
> runtime decision into a compile-time decision.
>
> Are you sure there's no way to simply select the correct baud rate on
> the port? I see plenty of references to configuring custom baud rates
> under Linux when I search Google, e.g.:
>
>> https://stackoverflow.com/questions/12646324/how-to-set-a-custom-baud-rate-on-linux
>>
> "How to set a custom baud rate on Linux?"
>
>> https://sourceware.org/ml/libc-help/2009-06/msg00016.html
> "Re: Terminal interface and non-standard baudrates"
>

I remember this gist from Peter Hurley:

https://gist.github.com/peterhurley/fbace59b55d87306a5b8