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 21:30:12 +0300
From: Dmitry Rokosov <ddrokosov@...utedevices.com>
To: Conor Dooley <conor@...nel.org>
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 04:48:33PM +0100, Conor Dooley wrote:
> 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?

Hmmm, correct. Okay, I see, I will support sys_pll as optional
connection :)

-- 
Thank you,
Dmitry