linux-kernel - Re: [PATCH v2 2/7] dt-bindings: clock: meson: a1: pll: introduce new syspll bindings

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Date: Mon, 13 May 2024 16:48:33 +0100
From: Conor Dooley <conor@...nel.org>
To: Dmitry Rokosov <ddrokosov@...utedevices.com>
Cc: neil.armstrong@...aro.org, jbrunet@...libre.com,
	mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org,
	krzysztof.kozlowski+dt@...aro.org, khilman@...libre.com,
	martin.blumenstingl@...glemail.com, jian.hu@...ogic.com,
	kernel@...rdevices.ru, rockosov@...il.com,
	linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/7] dt-bindings: clock: meson: a1: pll: introduce new
 syspll bindings

On Mon, May 13, 2024 at 12:18:02PM +0300, Dmitry Rokosov wrote:
> Hello Conor,
> 
> Thank you for quick review!
> 
> On Sat, May 11, 2024 at 02:08:03PM +0100, Conor Dooley wrote:
> > On Fri, May 10, 2024 at 12:08:54PM +0300, Dmitry Rokosov wrote:
> > > The 'syspll' PLL is a general-purpose PLL designed specifically for the
> > > CPU clock. It is capable of producing output frequencies within the
> > > range of 768MHz to 1536MHz.
> > > 
> > > The clock source sys_pll_div16, being one of the GEN clock parents,
> > > plays a crucial role and cannot be tagged as "optional". Unfortunately,
> > > it was not implemented earlier due to the cpu clock ctrl driver's
> > > pending status on the TODO list.
> > 
> > It's fine to not mark it optional in the binding, but it should be
> > optional in the driver as otherwise backwards compatibility will be
> > broken. Given this is an integral clock driver, sounds like it would
> > quite likely break booting on these devices if the driver doesn't treat
> > syspll_in as optional.
> > A lesson perhaps in describing the hardware entirely, even if the
> > drivers don't make use of all the information yet?
> 
> Yes, it's definitely the right lesson for me. However, without syspll or
> syspll_in, we cannot utilize CPU power management at all.

That's the status-quo, right? The incorrect dts would continue to not
support CPU power management and the new one with the correct description
would?

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