Re: [PATCH V4 8/8] arm64: dts: qcom: sm4450: add camera, display and gpu clock controller

[Ajit Pandey]

On 7/16/2024 4:09 PM, Konrad Dybcio wrote:
> On 16.07.2024 10:39 AM, Taniya Das wrote:
> > On 7/12/2024 6:10 PM, Konrad Dybcio wrote:
> > > On 12.07.2024 2:31 PM, Ajit Pandey wrote:
> > > > On 7/12/2024 5:52 PM, Konrad Dybcio wrote:
> > > > > On 12.07.2024 11:53 AM, Ajit Pandey wrote:
> > > > > > On 7/11/2024 3:25 PM, Konrad Dybcio wrote:
> > > > > > > On 3.07.2024 11:16 AM, Ajit Pandey wrote:
> > > > > > > > On 6/13/2024 1:11 PM, Konrad Dybcio wrote:
> > > > > > > > > On 6/11/24 15:37, Ajit Pandey wrote:
> > > > > > > > > > Add device node for camera, display and graphics clock controller on
> > > > > > > > > > Qualcomm SM4450 platform.
> > > > > > > > > >
> > > > > > > > > > Signed-off-by: Ajit Pandey <quic_ajipan@xxxxxxxxxxx>
> > > > > > > > > > ---
> > > > > > > > >
> > > > > > > > > None of these nodes reference a power domain (which would usually be
> > > > > > > > > CX/MX/MMCX). This way, the RPMhPDs will never be scaled.
> > > > > > > > >
> > > > > > > > > The current upstream implementation only allows one power domain to be
> > > > > > > > > scaled, but that's better than none (see other DTs for recent SoCs).
> > > > > > > > >
> > > > > > > > > Konrad
> > > > > > > >
> > > > > > > > SM4450 doesn't support MMCX and CX/MX domains will remain active so
> > > > > > > > power-domains property is actually not required for SM4450 clock nodes.
> > > > > > >
> > > > > > > It's not only about them being active.. some PLLs require e.g. MX to be
> > > > > > > at a certain level, or the system will be unstable
> > > > > > >
> > > > > > > Konrad
> > > > > >
> > > > > > With active I mean CX/MX rails will be default running at minimum level required for clock controllers. Adding power-domains property for CX/MX rails is like a redundant code as that will also scale such rails at default specified minimum level only. Also we hadn't added such property for other targets DT nodes to scale up CX/MX at minimum level.
> > > > >
> > > > > What I mean here is that, the minimum level may not be enough. In such case
> > > > > you would also add a required-opps = <&handle_to_rpmhpd_opp_level>
> > > > >
> > > > > Konrad
> > > >
> > > > Apologies, but could you please elaborate the use-case where minimum level isn't enough ? I guess for clock controllers configuration min level of CX/MX would be suffice, client will anyhow scale such rails to higher levels depending on their use-case.
> > >
> > > The main issue here is with PLLs within the clock controllers. Nobody
> > > votes for them. It's an unsolved problem and we currently work around
> > > cases where it's necessary by requiring that (with runtime pm, so when
> > > there's active consumers of the clock controller) the attached power
> > > domain is at >= SOME_LEVEL
> > >
> > > Konrad
> >
> > Konrad, this target (SM4450) have all the PLLs connected to CX/MX(again this is not collapsible). At boot the RPMHPD driver would keep the rails at minimum level and which is good to operate for the clock controller. I do not see currently this requirement you pose here specifically for SM4450.
> >
> > As part of the PLL requirement within clock controller, this is definitely a requirement which we plan to RFC soon. There are discussions already in progress on how to handle this requirement.
>
> Ok, if it works, let's keep it as is until that RFC
>
> Konrad

Thanks Konrad, please provide your ack on this patch if it looks fine 
for now.
--
Regards
Ajit