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

[Jagadeesh Kona]

Hi Dmitry,

Thanks for your review!

On 6/1/2023 8:13 PM, Dmitry Baryshkov wrote:
> 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@xxxxxxxxxxx>
> > > > > Signed-off-by: Jagadeesh Kona <quic_jkona@xxxxxxxxxxx>
> > > > > ---
> > > > 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.

Sure, will keep the existing code as is and will remove this patch in 
the next series.

> > 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.

The only difference between evo and ole pll configure is extra 
RINGOSC_CAL_L programming needed only for ole pll. We can achieve the 
same with clk_lucid_evo_pll_configure() itself by directly including 
RINGOSC_CAL_L field in L configuration for OLE PLL's.

Thanks & Regards,
Jagadeesh