Re: [PATCH 09/13] clk: qcom: cpu-8996: fix PLL configuration sequence

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 12/01/2023 16:32, Konrad Dybcio wrote:
> 
> 
> On 11.01.2023 23:05, Dmitry Baryshkov wrote:
>> On 11/01/2023 23:08, Konrad Dybcio wrote:
>>>
>>>
>>> On 11.01.2023 20:20, Dmitry Baryshkov wrote:
>>>> Switch both power and performance clocks to the GPLL0/2 (sys_apcs_aux)
>>>> before PLL configuration. Switch them to the ACD afterwards.
>>>>
>>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>>>> ---
>>>>    drivers/clk/qcom/clk-cpu-8996.c | 14 ++++++++++++++
>>>>    1 file changed, 14 insertions(+)
>>>>
>>>> diff --git a/drivers/clk/qcom/clk-cpu-8996.c b/drivers/clk/qcom/clk-cpu-8996.c
>>>> index 571ed52b3026..47c58bb5f21a 100644
>>>> --- a/drivers/clk/qcom/clk-cpu-8996.c
>>>> +++ b/drivers/clk/qcom/clk-cpu-8996.c
>>>> @@ -432,13 +432,27 @@ static int qcom_cpu_clk_msm8996_register_clks(struct device *dev,
>>>>    {
>>>>        int i, ret;
>>>>    +    /* Select GPLL0 for 300MHz for the both clusters */
>>> superfluous 'the'
>>>
>>>> +    regmap_write(regmap, PERFCL_REG_OFFSET + MUX_OFFSET, 0xc);
>>>> +    regmap_write(regmap, PWRCL_REG_OFFSET + MUX_OFFSET, 0xc);
>>>> +
>>>> +    /* Ensure write goes through before PLLs are reconfigured */
>>>> +    udelay(5);
>>> Is this value based on n clock cycles, or 'good enough'?
>>
>> Don't know, this is based on downstream direclty.
> Right, I see it now.
> 
>>
>>>
>>>> +
>>>>        clk_alpha_pll_configure(&pwrcl_pll, regmap, &hfpll_config);
>>>>        clk_alpha_pll_configure(&perfcl_pll, regmap, &hfpll_config);
>>>>        clk_alpha_pll_configure(&pwrcl_alt_pll, regmap, &altpll_config);
>>>>        clk_alpha_pll_configure(&perfcl_alt_pll, regmap, &altpll_config);
>>>>    +    /* Wait for PLL(s) to lock */
>>>> +        udelay(50);
>>> Weird indentation

Fixing for v2.

>>>
>>> Maybe wait_for_pll_enable_lock() to be super sure?
>>
>> Does it work for HWFSM PLLs?
> Not sure, but wait_for_pll_update_ack_clear() should, since it's
> called by

I'd prefer to keep it as is. First, this seems to be the difference 
between normal and hwfsm PLLs, see clk_alpha_pll_is_enabled() vs 
clk_alpha_pll_hwfsm_is_enabled(). And second, the wait_for_pll() 
function is not exported from the clk-alpha-pll.c. Note, that downstream 
also does sleep instead of waiting.

> 
> clk_alpha_pll_hwfsm_set_rate() ->
>    __clk_alpha_pll_set_rate() ->
>      clk_alpha_pll_update_latch() ->
>        __clk_alpha_pll_update_latch()
> 
> Konrad
>>
>>>
>>>> +
>>>>        qcom_cpu_clk_msm8996_acd_init(regmap);
>>>>    +    /* Switch clusters to use the ACD leg */
>>>> +    regmap_write(regmap, PWRCL_REG_OFFSET + MUX_OFFSET, 0x2);
>>>> +    regmap_write(regmap, PERFCL_REG_OFFSET + MUX_OFFSET, 0x2);
>>>> +
>>> No delays here?
>>
>> No. Probably it isn't required since there is no additional PLL locking, etc.
>>
>>>
>>> Konrad
>>>>        for (i = 0; i < ARRAY_SIZE(cpu_msm8996_hw_clks); i++) {
>>>>            ret = devm_clk_hw_register(dev, cpu_msm8996_hw_clks[i]);
>>>>            if (ret)
>>

-- 
With best wishes
Dmitry