Re: [PATCH V2 3/6] clk: qcom: clk-alpha-pll: Remove explicit CAL_L configuration for EVO PLL

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

On 01/06/2023 17:33, Jagadeesh Kona wrote:
> Hi Dmitry, Konrad,
> 
> On 5/26/2023 9:23 PM, Dmitry Baryshkov wrote:
>> On 26/05/2023 12:33, Konrad Dybcio wrote:
>>>
>>>
>>> On 25.05.2023 19:21, Jagadeesh Kona wrote:
>>>> In lucid evo pll, the CAL_L field is part of L value register 
>>>> itself, and
>>>> the l value configuration passed from clock controller driver includes
>>>> CAL_L and L values as well. Hence remove explicit configuration of 
>>>> CAL_L
>>>> for evo pll.
>>>>
>>>> Fixes: 260e36606a03 ("clk: qcom: clk-alpha-pll: add Lucid EVO PLL 
>>>> configuration interfaces")
>>>> Signed-off-by: Taniya Das <quic_tdas@quicinc.com>
>>>> Signed-off-by: Jagadeesh Kona <quic_jkona@quicinc.com>
>>>> ---
>>> Oh that isn't obvious at first sight, nice find!
>>>
>>> I'd suggest a different solution though:
>>>
>>> #define LUCID_EVO_PLL_L_LVAL    GENMASK(..
>>> #define LUCID_EVO_PLL_L_CAL_L    GENMASK(..
>>>
>>> lval = FIELD_PREP(LUCID_EVO_PLL_L_LVAL, config->l) |
>>>         FIELD_PREP(LUCID_EVO_PLL_L_CAL_L, config->cal_l);
>>>
>>> This would make the separation between the two parts more explicit
>>>
>>> however
>>>
>>> config->l would then represent the L value and not the end value
>>> written to the L register
>>
>> Yes. I think there should be separate config->l and config->cal_l 
>> values (and probably ringosc_cal_l, basing on the comment in the source).
>> Thanks for your suggestions. In all recent chipsets, L & CAL_L fields 
> are encapsulated in the same register, so we feel it is better to 
> directly pass the combined configuration value in config->l itself and 
> program it directly into register without any additional handling 
> required in pll driver code.

My feeling is that it is better to split it, since these are the 
different fields. The value .l = 0x4444003e doesn't mean anything per se.

Three values are much more meaningful:
.l = 0x3e,
.cal_l = 0x44,
.ringosc_cal_l = 0x44,

Not to mention that this way you don't have to touch pll configuration 
for the existing Lucid EVO PLL. Not to mention that for the Lucid ole 
PLLs the cal_l and ringosc_cal_l values seem to be static (0x44), so 
there is no need to put them to the variable data.

> 
> Also the evo pll code is currently reused for both lucid evo and ole 
> pll's. Lucid ole PLL has an additional RINGOSC_CAL_L field along with L, 
> CAL_L fields in the same L register. By passing combined configuration 
> value in config->l itself, we feel we can avoid all the additional 
> handling required in PLL code.
> 
>> Just a question: is camcc-sm8550 using the same PLL type or is it some 
>> kind of subtype of lucid_evo PLL?
>>
> No, it is not the same lucid evo PLL. It uses lucid ole PLL.

Then please don't reuse the clk_lucid_evo_pll_configure() call.
You can add a new one, which will handle L/CAL_L/RINGOSC_CAL_L differences.

-- 
With best wishes
Dmitry