linux-kernel - Re: [PATCH v3 1/2] dt-bindings: clock: sophgo: add clock controller for SG2044

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Message-ID: <txuujicelz5kbcnn3qyihwaspqrdc42z4kmijpwftkxlbofg2w@jsqmwj4lz662>
Date: Fri, 14 Mar 2025 06:46:22 +0800
From: Inochi Amaoto <inochiama@...il.com>
To: Stephen Boyd <sboyd@...nel.org>, Chen Wang <unicorn_wang@...look.com>, 
	Conor Dooley <conor+dt@...nel.org>, Inochi Amaoto <inochiama@...il.com>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Michael Turquette <mturquette@...libre.com>, 
	Richard Cochran <richardcochran@...il.com>, Rob Herring <robh@...nel.org>
Cc: linux-clk@...r.kernel.org, devicetree@...r.kernel.org, 
	sophgo@...ts.linux.dev, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	Yixun Lan <dlan@...too.org>, Longbin Li <looong.bin@...il.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: clock: sophgo: add clock controller
 for SG2044

On Thu, Mar 13, 2025 at 01:22:28PM -0700, Stephen Boyd wrote:
> Quoting Inochi Amaoto (2025-03-12 18:08:11)
> > On Wed, Mar 12, 2025 at 04:43:51PM -0700, Stephen Boyd wrote:
> > > Quoting Inochi Amaoto (2025-03-12 16:29:43)
> > > > On Wed, Mar 12, 2025 at 04:14:37PM -0700, Stephen Boyd wrote:
> > > > > Quoting Inochi Amaoto (2025-03-11 16:31:29)
> > > > > > 
> > > > > > > or if that syscon node should just have the #clock-cells property as
> > > > > > > part of the node instead.
> > > > > > 
> > > > > > This is not match the hardware I think. The pll area is on the middle
> > > > > > of the syscon and is hard to be separated as a subdevice of the syscon
> > > > > > or just add  "#clock-cells" to the syscon device. It is better to handle
> > > > > > them in one device/driver. So let the clock device reference it.
> > > > > 
> > > > > This happens all the time. We don't need a syscon for that unless the
> > > > > registers for the pll are both inside the syscon and in the register
> > > > > space 0x50002000. Is that the case? 
> > > > 
> > > > Yes, the clock has two areas, one in the clk controller and one in
> > > > the syscon, the vendor said this design is a heritage from other SoC.
> > > 
> > > My question is more if the PLL clk_ops need to access both the syscon
> > > register range and the clk controller register range. What part of the
> > > PLL clk_ops needs to access the clk controller at 0x50002000?
> > > 
> > 
> > The PLL clk_ops does nothing, but there is an implicit dependency:
> > When the PLL change rate, the mux attached to it must switch to 
> > another source to keep the output clock stable. This is the only
> > thing it needed.
> 
> I haven't looked at the clk_ops in detail (surprise! :) but that sounds
> a lot like the parent of the mux is the PLL and there's some "safe"
> source that is needed temporarily while the PLL is reprogrammed for a
> new rate. Is that right? I recall the notifier is in the driver so this
> sounds like that sort of design.

You are right, this design is like what you say. And this design is 
the reason that I prefer to just reference the syscon node but not
setting the syscon with "#clock-cell".

Regards,
Inochi