linux-kernel - Re: [PATCH v7] clk: add si5351 i2c common clock driver

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Message-ID: <CABJ1b_S_Tz9WBuO1==7ZU-fuAnYRwRZUcLCM=Zq+6tLCZyEevw@mail.gmail.com>
Date:	Thu, 11 Apr 2013 10:22:48 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Michal Bachraty <michal.bachraty@...eamunlimited.com>
Cc:	Daniel Mack <zonque@...il.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Mike Turquette <mturquette@...aro.org>,
	Stephen Warren <swarren@...dia.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Dom Cobley <popcornmix@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rabeeh Khoury <rabeeh@...id-run.com>,
	Jean-Francois Moine <moinejf@...e.fr>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Guenter Roeck <linux@...ck-us.net>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7] clk: add si5351 i2c common clock driver

On Thu, Apr 11, 2013 at 9:44 AM, Michal Bachraty
<michal.bachraty@...eamunlimited.com> wrote:
> On Wednesday, April 10, 2013 19:27:25 Sebastian Hesselbarth wrote:
>> Hmm, is there any driver using the clock output? Does it
>> clk_prepare_enable() the clock? I tend not to mess with anything the
>> bootloader or eeprom config left disabled. It works for me, but here the
>> driver will prepare/enable the clock prior use.
>
> For my case, disabled clock outputs in bootloader are correct. I'm working on
> module board with lot of purposes. For one I need to tune frequncy, for other
> not. In some cases I can use  clk_prepare_enable. For now, I need to tune clk,
> so I can't use clk_prepare_enable. Si5351 chip has no problem with enabling
> clock output multiple times, when calling clk_set_rate. So if this feature
> will not be in driver, I need to stay with patch upon driver.

Michal,

after thinking about it, I will re-add the power-on on rate change.
Not because I
want to have a workaround for not using clk_prepare_enable() before
clk_set_rate(),
but clkout will remain disabled if you set clock-frequency by DT.
There will be no
superfluous writes to i2c resisters anyway, because clk-si5351 is
using regmap-i2c
that takes care of caching.

Sebastian
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