linux-kernel - Re: [PATCH 2/2] clk: qcom: gcc-sc8280xp: Don't keep display AHB clocks always-on

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Date:   Mon, 2 Oct 2023 10:34:02 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 2/2] clk: qcom: gcc-sc8280xp: Don't keep display AHB
 clocks always-on

On Sat, Sep 30, 2023 at 06:44:47PM +0200, Konrad Dybcio wrote:
> On 9/30/23 11:39, Johan Hovold wrote:
> > On Fri, Sep 29, 2023 at 03:38:53PM +0200, Konrad Dybcio wrote:
> >> These clocks are consumed by the dispcc[01] clock controllers, so there's
> >> no reason to keep them on from gcc probe. Remove that hack.
> > 
> > Eh, how did you test this patch?

> Oehh you're right, I didn't notice that I still had clk_ignore_unused :/

That doesn't matter since these clocks are never even registered with
the clock framework.

But you'd notice that if you try to verify the clock state by looking at
/sys/kernel/debug/clk/clk_summary for example.

> > The GCC_DISP_AHB_CLK clocks are not modelled by the clock driver
> > currently so nothing is guaranteeing them to be enabled if we were to
> > apply this patch. They just happen to be left on by the bootloader on
> > some machines currently (well at least one of them is on one machine).

> What fooled me is that despite not being modeled by the clock driver, it 
> is defined in bindings and referenced in the device tree.
> 
> Another thing I'll fix up!

Right, a number of Qualcomm SoCs apparently fail to register these
clocks. You should start by determining why that is as I assume (hope)
it was done for a reason.

Then the Qualcomm drivers use sloppy bulk clock look-up and enable so
that an integrator would never even notice when clocks are missing. Once
the clocks are registered, that could be tightened up as well.

Johan