linux-kernel - Re: [PATCH v5 0/2] Add notifier for PLL0 clock and set it 1.5GHz on

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Date: Tue, 14 May 2024 19:07:58 +0100
From: Conor Dooley <conor@...nel.org>
To: Xingyu Wu <xingyu.wu@...rfivetech.com>
Cc: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Emil Renner Berthing <emil.renner.berthing@...onical.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Hal Feng <hal.feng@...rfivetech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
	"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 0/2] Add notifier for PLL0 clock and set it 1.5GHz on

On Tue, May 14, 2024 at 07:40:02AM +0000, Xingyu Wu wrote:
> On 11/05/2024 20:19, Conor Dooley wrote:
> > 
> > On Sat, May 11, 2024 at 03:02:56AM +0000, Xingyu Wu wrote:
> > > On 11/05/2024 05:05, Conor Dooley wrote:
> > > >
> > > > On Tue, May 07, 2024 at 02:53:17PM +0800, Xingyu Wu wrote:
> > > > > This patch is to add the notifier for PLL0 clock and set the PLL0
> > > > > rate to 1.5GHz to fix the lower rate of CPUfreq on the JH7110 SoC.
> > > > >
> > > > > The first patch is to add the notifier for PLL0 clock. Setting the
> > > > > PLL0 rate need the son clock (cpu_root) to switch its parent clock
> > > > > to OSC clock and switch it back after setting PLL0 rate. It need
> > > > > to use the cpu_root clock from SYSCRG and register the notifier in
> > > > > the SYSCRG driver.
> > > > >
> > > > > The second patch is to set cpu_core rate to 500MHz and PLL0 rate
> > > > > to 1.5GHz to fix the problem about the lower rate of CPUfreq on
> > > > > the visionfive board. The cpu_core clock rate is set to 500MHz
> > > > > first to ensure that the cpu frequency will not suddenly become
> > > > > high and the cpu voltage is not enough to cause a crash when the PLL0 is set
> > to 1.5GHz.
> > > > > The cpu voltage and frequency are then adjusted together by CPUfreq.
> > > >
> > > > Hmm, how does sequencing work here? If we split the patches between
> > > > trees it sounds like without the dts patch, the clock tree would (or
> > > > could) crash, or mainline if the clock changes there before the dts
> > > > ones do. Am I misunderstanding that?
> > >
> > > Oh, I think you misunderstood it. Patch 1 (clock driver patch) does
> > > not cause the clock tree crash without the patch 2 (dts patch), and it
> > > just provides the correct flow of how to change the PLL0 rate. The
> > > patch 2 is to set the clock rate of cpu_core and PLL0 rate, which
> > > causes the crash without patch 1. Setting cpu_core rate is to avoid crashes by
> > insufficient cpu voltage when setting PLL0 rate.
> > 
> > So is the problem in the other direction then? My dts tree will crash if I apply the
> > dts change without the clock patch?
> 
> Sorry, I tested it and it could not crash using only dts patch. It can separate the
> patches and use it individually.
> 
> > Additionally, what about U-Boot? Will it have problems if the dts is imported
> > there without changes to its clock driver?
> > 
> 
> It is not apply to U-Boot. In the U-Boot, the PLL0 rate should be 1GHz to for GMAC
> and PMIC to work. But now the PLL0 rate should be 1.5GHz in the Linux.

There's a push in U-Boot to move devicestrees to use "OF_UPSTREAM",
which means importing devicetrees directly from Linux and using them in
U-Boot. I don't really want to merge a patch that would present U-Boot
with a problem if the VisionFive 2 moved to that model there.

Cheers,
Conor.

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