[linux-sunxi] Problem with Allwinner H3 clocks

[Chen-Yu Tsai]

Hi,

On Mon, Feb 1, 2016 at 10:26 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> 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:
>>>
>>> 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).
>
>
> 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.

The mod clocks do not have CLK_SET_RATE_PARENT set, which prevents the
CCF from propagating clk_set_rate to its parent. As is for the other
child clocks of PLL6. The only exception is the SATA clock in PLL6.

Regards
ChenYu