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

From: Dmitry Baryshkov
Date: Thu Jun 01 2023 - 10:44:22 EST


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.


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