linux-kernel - Re: [PATCH v2] arm64/dts/qcom/sc7180: Add Display Port dt node

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Date:   Tue, 8 Jun 2021 17:26:23 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     khsieh@...eaurora.org, robdclark@...il.com, sean@...rly.run,
        vkoul@...nel.org, agross@...nel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, abhinavk@...eaurora.org,
        aravindh@...eaurora.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64/dts/qcom/sc7180: Add Display Port dt node

On Tue 08 Jun 17:15 CDT 2021, Stephen Boyd wrote:

> Quoting Bjorn Andersson (2021-06-07 16:31:47)
> > On Mon 07 Jun 12:48 CDT 2021, khsieh@...eaurora.org wrote:
> >
> > > On 2021-06-05 22:07, Bjorn Andersson wrote:
> > > > On Thu 03 Jun 16:56 CDT 2021, khsieh@...eaurora.org wrote:
> > > >
> > > > > On 2021-06-03 09:53, Bjorn Andersson wrote:
> > > > > > On Thu 03 Jun 11:09 CDT 2021, Kuogee Hsieh wrote:
> > > > [..]
> > > > > > > diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> > > > [..]
> > > > > > > +                             power-domains = <&rpmhpd SC7180_CX>;
> > > > > >
> > > > > > Just curious, but isn't the DP block in the MDSS_GDCS? Or do we need to
> > > > > > mention CX here in order for the opp framework to apply required-opps
> > > > > > of CX?
> > > > >
> > > > > yes,
> > > >
> > > > If you want me, or other maintainers, to spend any time reviewing or
> > > > applying your patches going forward then you need to actually bother
> > > > replying properly to the questions asked.
> > > >
> > > > Thanks,
> > > > Bjorn
> > >
> > > Sorry about the confusion. What I meant is that even though DP controller is
> > > in the MDSS_GDSC
> > > power domain, DP PHY/PLL sources out of CX. The DP link clocks have a direct
> > > impact
> > > on the CX voltage corners. Therefore, we need to mention the CX power domain
> > > here. And, since
> > > we can associate only one OPP table with one device, we picked the DP link
> > > clock over other
> > > clocks.
> >
> > Thank you, that's a much more useful answer.
> >
> > Naturally I would think it would make more sense for the PHY/PLL driver
> > to ensure that CX is appropriately voted for then, but I think that
> > would result in it being the clock driver performing such vote and I'm
> > unsure how the opp table for that would look.
> >
> > @Stephen, what do you say?
> >
> 
> Wouldn't the PHY be the one that sets some vote? So it wouldn't be the
> clk driver, and probably not from the clk ops, but instead come from the
> phy ops via phy_enable() and phy_configure().
> 

If I understand the logic correctly *_configure_dp_phy() will both
configure the vco clock and "request" the clock framework to change the
rate.

So I presume what you're suggesting is that that would be the place to
cast the CX corner vote?

> By the way, there's nothing wrong with a clk device doing power domain
> "stuff", except for that we haven't plumbed it into the clk framework
> properly and I'm fairly certain our usage of runtime PM in the clk
> framework today underneath the prepare_lock is getting us into trouble
> or will get us there soon.

On the bright side, it's wonderful that we're at a point where this is
not only a theoretical problem :)

Regards,
Bjorn