Message-ID: <20130211054632.11471.24295@quantum>
Date:	Sun, 10 Feb 2013 21:46:32 -0800
From:	Mike Turquette <mturquette@...aro.org>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	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>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rabeeh Khoury <rabeeh@...id-run.com>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clk: add si5351 i2c common clock driver

Quoting Sebastian Hesselbarth (2013-02-09 04:59:32)
> This patch adds a common clock driver for Silicon Labs Si5351a/b/c
> i2c programmable clock generators. Currently, the driver supports
> DT kernels only and VXCO feature of si5351b is not implemented. DT
> bindings selectively allow to overwrite stored Si5351 configuration
> which is very helpful for clock generators with empty eeprom
> configuration. Corresponding device tree binding documentation is
> also added.
> 
> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
> ---
> Notes:
> - During development I used a debugfs clock consumer that I can also
>   post if there is interest in it.

Please do.  I have a set of patches that implement a fake clock subtree
for testing the core framework.  I've been thinking of pushing this to
the list once it is more presentable and your work might fit into that
nicely.

> - With current (3.8-rc6) common clock framework there is two (minor)
>   issues:
>   * although clocks are registered with devm_clk_register they are not
>     removed from the clock tree on unloading. That makes reloading of
>     clk-si5351 as module impossible.

This is a known issue.  clk_unregister is a NOP and defining it has
always been deferred until the day that someone needed it.  Care to
take a crack at it?

>   * potentially there could be more than one different external si5351
>     generators but clocks are registered with names that do not refer
>     to e.g. the device name. Maybe common clock framework should
>     prepend the device name for each registered clock, i.e. 0-0060.clk0.
>     That would also avoid name collisions with same clock names from
>     different drivers (clk0 is likely to be used by others ;))

More unfinished work, just like clk_unregister above.  I'm sure you are
aware that clk_register takes struct device *dev as input, but does
nothing with it.  It wouldn't take much to concatenate the device name
and clock name if dev is present.  However a complication here is that
the registration code takes a parent string name to match parents up for
discrete subtrees; how could statically defined data know about the
device name ahead of time?

The above design decision took place before the big DT push we have
today and was short-sighted.  It would be better to change the framework
to rely less on string name lookups and DT is one way out of that.

3.8-rc7 is already out and I don't plan to take anything that hasn't
already been submitted for 3.9 now.  Can you resubmit this after 3.9-rc1
comes out?

Thanks,
Mike
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