Re: Heads up: new SD controller driver for Raspberry Pi in -current

[Harold Gutch <logix%foobar.franken.de@localhost>]

On Thu, Aug 17, 2017 at 07:20:06AM -0300, Jared McNeill wrote:
> On Thu, 17 Aug 2017, Jared McNeill wrote:
> 
> >On Thu, 17 Aug 2017, Harold Gutch wrote:
> >
> >>Oh, does that also apply to the Pi 3 and Zero W then?  I haven't yet
> >>felt the need to overclock any of my Raspberries but it would of
> >>course be good to know any such caveats.  From what I've read,
> >>force_turbo=1 will disable dynamic clocking and make the Raspberry
> >>always run on machdep.cpu.frequency.max (I guess) while force_turbo=0
> >>will allow it to also run at slower speeds (down to frequency.min?).
> >>At least that is how it apparently works in Linux...
> >
> >I think you're right -- I misunderstood the documentation for how 
> >force_turbo=0 applies to the core freq. I'm looking for something I can 
> >put in config.txt that will keep core freq at a fixed rate, is applicable 
> >to all boards, and doesn't set the warranty bit. Any suggestions?
> 
> I checked with the documentation and it jogged my memory: enable_uart=1 is 
> what causes core freq to stay consistent. I added force_turbo=0 (default 
> value anyway) to config.txt as an example for how to increase the core 
> clock speed. As long as enable_uart=1 is set, the core clock will be 
> consistent.
> 
> Hope this helps,

Ah, OK, this explains quite a bit.  A while back I also read about
problems with the UART if the core frequency is dynamic.
enable_uart=1 fixes the core frequency, either to core_freq_min (if
force_turbo=0) or to core_freq (if force_turbo=1).

And I think just setting force_turbo=1 does not yet set the warranty
bit, that is only set if you *additionally* set one of the
over_voltage_* variables (even setting "over_voltage" in addition to
force_turbo=1 does not yet set the warranty bit).

Thanks for clarifying, I already thought sdhost only worked with fixe
core frequencies, that surprised me a bit since I so far haven't read
anything of that kind in combination with Raspbian.


  Hrold