[linux-sunxi] Problem with Allwinner H3 clocks

Hi,

On 01-02-16 07:37, Maxime Ripard wrote:

Hi,

On Fri, Jan 29, 2016 at 07:25:51AM +0100, Hans de Goede wrote:

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Hi,

On 01/28/2016 08:29 PM, Maxime Ripard wrote:

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On Thu, Jan 28, 2016 at 05:59:18PM +0100, Jean-Francois Moine wrote:

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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).

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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).

Shouldn't we be opt-ing in then ? At least the mmc driver makes
clk_set_rate calls, it would be bad if that somehow ends up changing the
pll6 rate while other peripherals are using it.

Regards,

Hans