linux-kernel - Re: [PATCH 6/7] clk: scmi: Allocate CLK operations dynamically

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Message-ID: <ZeBXxjKiDMT2YPtP@pluto>
Date: Thu, 29 Feb 2024 10:09:10 +0000
From: Cristian Marussi <cristian.marussi@....com>
To: Stephen Boyd <sboyd@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	sudeep.holla@....com, james.quinlan@...adcom.com,
	f.fainelli@...il.com, vincent.guittot@...aro.org,
	peng.fan@....nxp.com, michal.simek@....com, quic_sibis@...cinc.com,
	quic_nkela@...cinc.com, souvik.chakravarty@....com,
	Michael Turquette <mturquette@...libre.com>,
	linux-clk@...r.kernel.org
Subject: Re: [PATCH 6/7] clk: scmi: Allocate CLK operations dynamically

On Wed, Feb 28, 2024 at 06:20:34PM -0800, Stephen Boyd wrote:
> Quoting Cristian Marussi (2024-02-22 00:28:41)
> > On Wed, Feb 21, 2024 at 09:44:14PM -0800, Stephen Boyd wrote:
> > > 
> > > It's not great to move these function pointer structs out of RO memory
> > > to RW. I'm also not convinced that it's any better to construct them at
> > > runtime. Isn't there a constant set of possible clk configurations? Or
> > > why can't we simply add some failures to the clk_ops functions instead?
> > 
> > Well, the real clock devices managed by the SCMI server can be a of
> 
> SCMI is a server!? :)
> 

..well the platform fw act as a server in the client-server SCMI
model...so...I know these days it's cooler to be "serverless" but..hey...
..at least is not a BO2k server :P

> > varying nature and so the minimum set of possible clk configurations
> > to cover will amount to all the possible combinations of supported ops
> > regarding the specific clock properties (i.e. .set_parent / .set_rate /
> > .enable / .get/set_duty_cycle / atomic_capability ... for now)...we
> > simply cannot know in advance what the backend SCMI server is handling.
> > 
> > These seemed to me too much in number (and growing) to be pre-allocated
> > in all possible combinations. (and mostly wasted since you dont really
> > probably use all combinations all the time)
> > 
> > Moreover, SCMI latest spec now exposes some clock properties (or not) to
> > be able avoid even sending an actual SCMI message that we know will be
> > denied all the time; one option is that we return an error,, as you said,
> > but what is the point (I thought) to provide at all a clk-callback that
> > we know upfront will fail to be executed every time ? (and some consumer
> > drivers have been reported by partners not to be happy with these errors)
> > 
> > What I think could be optimized here instead, and I will try in the next
> > respin, it is that now I am allocating one set of custom ops for each clock
> > at the end, even if exactly the same ops are provided since the clock
> > capabilities are the same; I could instead allocate dynamically and fill only
> > one single set of ops for each distinct set of combinations, so as to avoid
> > useless duplication and use only the miminum strict amount of RW memory
> > needed.
> > 
> 
> Yes please don't allocate a clk_op per clk. And, please add these
> answers to the commit text so that we know why it's not possible to know
> all combinations or fail clk_ops calls.

Sure I posted this series a couple of days ago about this rework:

	https://lore.kernel.org/linux-arm-kernel/20240227194812.1209532-1-cristian.marussi@arm.com/

with a bit of context in the cover-letter and in the commit...but I can
add more commenting of course if needed.

Thanks for the review,
Cristian