[U-Boot] [PATCH 4/7] ARM: sun6i: Add clock support

[Chen-Yu Tsai]

On Mon, Sep 22, 2014 at 9:15 PM, Ian Campbell <ijc at hellion.org.uk> wrote:
> On Mon, 2014-09-22 at 20:47 +0800, Chen-Yu Tsai wrote:
>> On Mon, Sep 22, 2014 at 2:35 AM, Ian Campbell <ijc at hellion.org.uk> wrote:
>> > On Mon, 2014-09-08 at 21:28 +0800, Chen-Yu Tsai wrote:
>> >> +     /* Set PLL ldo voltage without this PLL6 does not work properly */
>> >
>> > Is "this" here the doing it 3 times bit? If that's deliberate then
>> > please say so explicitly. e.g. "Set PLL LDO voltage 3 times, without ...
>> > etc"), if it's not deliberate then please fix ;-)
>>
>> Hans, if you could enlighten us? :)
>>
>> > I'm assuming this is one of those "no docs, allwinner code did it but
>> > nobody knows why it works" scenarios. Of course if the reason is
>> > known/doc'd then please add a reference.
>>
>> I looked at the boot1 sources we recently got.
>>
>> First it sets PRCM_PLL_CTRL_LDO_KEY to enable write access to the other
>> values.
>>
>> Then it sets PRCM_PLL_CTRL_IN_PWR_HIGH (which is the default) and
>> PRCM_PLL_CTRL_LDO_OUT_L(1140) in one call.
>>
>> Then it busy loops for some time to wait for it to stabilize.
>
> My guess would be that 3 writes happens to cause enough time to pass
> that things have (often!) stabilised, which is certainly not as good as
> an explicit waiting busy loop. But as you say lets see what Hans says.

FYI I'm dropping this part from the patch, so this discussion is for
future reference. :)

>> >> +     writel(PRCM_PLL_CTRL_LDO_DIGITAL_EN | PRCM_PLL_CTRL_LDO_ANALOG_EN |
>> >> +             PRCM_PLL_CTRL_EXT_OSC_EN | PRCM_PLL_CTRL_LDO_OUT_L(1140) |
>> >> +             PRCM_PLL_CTRL_LDO_KEY, &prcm->pll_ctrl1);
>> >> +     writel(PRCM_PLL_CTRL_LDO_DIGITAL_EN | PRCM_PLL_CTRL_LDO_ANALOG_EN |
>> >> +             PRCM_PLL_CTRL_EXT_OSC_EN | PRCM_PLL_CTRL_LDO_OUT_L(1140) |
>> >> +             PRCM_PLL_CTRL_LDO_KEY, &prcm->pll_ctrl1);
>> >> +     writel(PRCM_PLL_CTRL_LDO_DIGITAL_EN | PRCM_PLL_CTRL_LDO_ANALOG_EN |
>> >> +             PRCM_PLL_CTRL_EXT_OSC_EN | PRCM_PLL_CTRL_LDO_OUT_L(1140),
>> >> +             &prcm->pll_ctrl1);
>> > [...]