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

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Date:   Tue, 8 Jun 2021 17:34:01 -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 17:29 CDT 2021, Stephen Boyd wrote:

> Quoting Bjorn Andersson (2021-06-08 15:26:23)
> > 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:
> > > >
> > > > > 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?
> 
> Yes that would be a place to make the CX vote. The problem is then I
> don't know where to drop the vote. Is that when the phy is disabled?

We do pass qcom_qmp_phy_power_off() and power down the DP part as DP
output is being disabled. So that sounds like a reasonable place to drop
the vote for the lowest performance state.

Regards,
Bjorn