Re: [PATCH 0/3] Add support to reconfigure PLL

[Taniya Das]

On 2/4/2025 3:38 PM, Johan Hovold wrote:
> On Mon, Jan 13, 2025 at 10:57:03PM +0530, Taniya Das wrote:
> > During boot-up, there is a possibility that the PLL configuration might
> > be missed even after invoking pll_configure() from the clock controller
> > probe. This is often due to the PLL being connected to rail or rails
> > that are in an OFF state and current clock controller also cannot vote
> > on multiple rails. As a result, the PLL may be enabled with suboptimal
> > settings, leading to functional issues.
> >
> > The PLL configuration, now part of clk_alpha_pll, can be reused to
> > reconfigure the PLL to a known good state before scaling for frequency.
> > The 'clk_alpha_pll_reconfigure()' can be updated to support more PLLs
> > in future.
>
> This sounds like a hack. You already describe the underlying problem (and
> indirectly its solution) in the first paragraph above, namely that the
> video clock controller has not enabled the power domain needed to
> configure the PLL.

This is not a hack, but another alternative way to ensure the PLL is 
configured to the right configuration before being used.

> I believe support for clock controllers that need to enable multiple
> power domains is on its way into 6.15:
>
> 	https://lore.kernel.org/lkml/20250117-b4-linux-next-24-11-18-clock-multiple-power-domains-v10-0-13f2bb656dad@xxxxxxxxxx/
>
> Perhaps that's what you need to fix this properly.

Yes, this is just to add a dependency on clock controller to put the 
rail vote, but this series does not fully solve the clock controller's 
PLL requirement problems.

> > The IRIS driver support added
> > https://lore.kernel.org/all/20241212-qcom-video-iris-v9-0-e8c2c6bd4041@xxxxxxxxxxx/
> > observes the pll latch warning during boot up due to the dependency of
> > the PLL not in good state, thus add config support for SM8550 Video
> > clock controller PLLs.
>
> > Taniya Das (3):
> >        clk: qcom: clk-alpha-pll: Integrate PLL configuration into PLL structure
> >        clk: qcom: clk-alpha-pll: Add support to reconfigure PLL
> >        clk: qcom: videocc-sm8550: Update the pll config for Video PLLs
>
> Johan

--
Thanks & Regards,
Taniya Das.