linux-kernel - Re: [PATCH v3 1/2] clk: qcom: dispcc-sc7180: Only park display clks at init

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Message-ID: <CAE-0n51Ag1wpj0uUPVtMvgZJE2FF_FZkw+j=bRiAq3vYk=Y_Fw@mail.gmail.com>
Date: Thu, 29 Aug 2024 09:34:05 -0700
From: Stephen Boyd <swboyd@...omium.org>
To: Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Stephen Boyd <sboyd@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	patches@...ts.linux.dev, linux-clk@...r.kernel.org, 
	Amit Pundir <amit.pundir@...aro.org>, Taniya Das <quic_tdas@...cinc.com>
Subject: Re: [PATCH v3 1/2] clk: qcom: dispcc-sc7180: Only park display clks
 at init

Quoting Neil Armstrong (2024-08-29 08:32:48)
>
>
> I've been testing this serie on SM8650, and with 01a0a6cc8cfd ("clk: qcom: Park shared RCGs upon registration")
> it fixes an issue we have that triggers:
> [   18.740736] ------------[ cut here ]------------
> [   18.745837] ufs_phy_gdsc status stuck at 'off'
> [   18.745929] WARNING: CPU: 1 PID: 197 at drivers/clk/qcom/gdsc.c:178 gdsc_toggle_logic+0x15c/0x164
> ...
> after waking up UFS from runtime suspend.

Oof that's not good.

>
> So I suspect we'll need to figure out which SM8650 GCC shared clocks would need
> to use clk_rcg2_shared_init_park_ops ?
>
> We also had random boot crash when initializing the display very late on multiple platforms,
> and so far "clk: qcom: Park shared RCGs upon registration" fixed that, but I also suppose Ill
> need to reflect the changes done to dispcc-sc7180.c to dispcc-sm8650.c and others.

It sounds like it's better to make the default always park at
registration time and special case the one or two places where that
isn't possible, i.e. USB because it has special rate requirements. So I
should just go back to v1 then and pile on the QUP patches.

In the long run we probably need to put the clk rate and enable control
into the pm_domains for the gdscs that require them and implement the
"parking" and "unparking" there instead of in the clk_ops layer. That
way we know that when the gdsc is turned on it will have a clk that
works, and when it is turned off it is always parked. We can also use
the gdsc on/off state at init time to increment the enable count on the
shared PLLs by using clk_hw_get_clk() and clk consumer APIs. This will
let us move the boot state into the kernel in a way that doesn't break
when a child clk sharing a PLL is turned off.