[linux-sunxi] Problem with Allwinner H3 clocks

[maxime.ripard@free-electrons.com (Maxime Ripard)]

Hi,

On Fri, Jan 29, 2016 at 07:25:51AM +0100, Hans de Goede wrote:
> Hi,
> 
> On 01/28/2016 08:29 PM, Maxime Ripard wrote:
> >On Thu, Jan 28, 2016 at 05:59:18PM +0100, Jean-Francois Moine wrote:
> 
> <snip>
> 
> >>The A23/A33/H3 (and surely some other SoCs) documentations about
> >>the peripheral/periph/periph0/periph1 PLLs say:
> >>
> >>	Note: The PLL Output should be fixed to 600MHz, it is not
> >>	recommended to vary this value arbitrarily.
> >
> >I don't know if it's worth it at this point. The pll6 seems to work
> >fine at other rates. Have you experienced any breakage when running at
> >another frequency?
> 
> Hmm, are we actually changing the freq of pll6 on any SoCs? I know we've
> the code to it, but given that it is shared between many pheripherals,
> I assume we end up never changing it.

We don't, but it works. Back when I was debugging the A31 DMA
controller, I tried to do just that and nothing broke (at least as
long as you don't switch halfway through during the boot, but at the
time the clock is registered).

> I assume / hope that the clock framework protects against reclocking
> a clock with multiple users ...

There is, but it's opt-in, and we're not using it yet for anything but
the hstimers (and in that case, we don't prevent the reclocking, we
just take it into account).

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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