linux-kernel - Re: [PATCH v3 0/2] clk: improve handling of orphan clocks

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Message-ID: <20150501001901.GC32407@codeaurora.org>
Date:	Thu, 30 Apr 2015 17:19:01 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Heiko Stuebner <heiko@...ech.de>
Cc:	mturquette@...aro.org, dianders@...omium.org,
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Alex Elder <elder@...aro.org>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Max Filippov <jcmvbkbc@...il.com>, kernel@...gutronix.de,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Chao Xie <chao.xie@...vell.com>,
	Jason Cooper <jason@...edaemon.net>,
	Stefan Wahren <stefan.wahren@...e.com>,
	Andrew Bresticker <abrestic@...omium.org>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Georgi Djakov <georgi.djakov@...aro.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Barry Song <baohua@...nel.org>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	Viresh Kumar <viresh.linux@...il.com>,
	Gabriel FERNANDEZ <gabriel.fernandez@...com>,
	emilio@...pez.com.ar, Peter De Schrijver <pdeschrijver@...dia.com>,
	Tero Kristo <t-kristo@...com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH v3 0/2] clk: improve handling of orphan clocks

On 04/22, Heiko Stuebner wrote:
> Using orphan clocks can introduce strange behaviour as they don't have
> rate information at all and also of course don't track 
> 
> This v2/v3 takes into account suggestions from Stephen Boyd to not try to
> walk the clock tree at runtime but instead keep track of orphan states
> on clock tree changes and making it mandatory for everybody from the
> start as orphaned clocks should not be used at all.
> 
> 
> This fixes an issue on most rk3288 platforms, where some soc-clocks
> are supplied by a 32khz clock from an external i2c-chip which often
> is only probed later in the boot process and maybe even after the
> drivers using these soc-clocks like the tsadc temperature sensor.
> In this case the driver using the clock should of course defer probing
> until the clock is actually usable.
> 
> 
> As this changes the behaviour for orphan clocks, it would of course
> benefit from more testing than on my Rockchip boards. To keep the
> recipent-list reasonable and not spam to much I selected one (the topmost)
> from the get_maintainer output of each drivers/clk entry.
> Hopefully some will provide Tested-by-tags :-)
> 

<grumble> I don't see any Tested-by: tags yet </grumble>. I've
put these two patches on a separate branch "defer-orphans" and
pushed it to clk-next so we can give it some more exposure.

Unfortunately this doesn't solve the orphan problem for non-OF
providers. What if we did the orphan check in __clk_create_clk()
instead and returned an error pointer for orphans? I suspect that
will solve all cases, right?

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
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