linux-kernel - Re: [v5] clk: add si5351 i2c common clock driver

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Date:	Mon, 8 Apr 2013 07:54:07 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	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>,
	Daniel Mack <zonque@...il.com>,
	Jean-Francois Moine <moinejf@...e.fr>,
	Lars-Peter Clausen <lars@...afoo.de>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [v5] clk: add si5351 i2c common clock driver

On Mon, Apr 08, 2013 at 08:11:38AM +0200, Sebastian Hesselbarth wrote:
> On 04/08/2013 02:17 AM, Guenter Roeck wrote:
> >On Mon, Apr 08, 2013 at 01:49:24AM +0200, Sebastian Hesselbarth wrote:
> >>On 04/08/2013 12:50 AM, Guenter Roeck wrote:
> >>>On Fri, Apr 05, 2013 at 05:23:35AM -0000, Sebastian Hesselbarth wrote:
> >>>>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>
> >>>>Tested-by: Daniel Mack<zonque@...il.com>
> >>>>
> >>>[ ... ]
> >>>
> >>>>+static inline void _si5351_msynth_set_pll_master(
> >>>>+	struct si5351_driver_data *drvdata, unsigned char num, int is_master)
> >>>>+{
> >>>>+	unsigned long flags;
> >>>>+
> >>>>+	if (num>   8 ||
> >>>>+	    (drvdata->variant == SI5351_VARIANT_A3&&   num>   3))
> >>>>+		return;
> >>>>+
> >>>>+	flags = __clk_get_flags(drvdata->msynth[num].hw.clk);
> >>>>+	if (is_master)
> >>>>+		flags |= CLK_SET_RATE_PARENT;
> >>>>+	else
> >>>>+		flags&= ~CLK_SET_RATE_PARENT;
> >>>>+	__clk_set_flags(drvdata->msynth[num].hw.clk, flags);
> >>>>+}
> >>>>+
> >>>Unless I am missing something, neither __clk_get_flags() nor the new
> >>>__clk_set_flags is exported.
> >>>
> >>>Did you try to build and load the driver as module ?
> >>
> >>Well, good catch. I didn't try to build v5 as a module, but I guess it
> >>will fail. But I consider this as something that has to be addressed in
> >>clk framework itself, not in this patch. There will be other
> >>clk-providers built as module in the future for sure.
> >>
> >Sure, but you provided the patch to make __clk_set_flags global. To avoid
> >build failures, I would suggest to either submit a patch to export the
> >missing functions, or to remove the ability to build the driver as module.
> 
> Actually, I knew that __clk_set_flags patch will not be accepted
> before posting it ;)
> 
Ah, but part of that is to get you to think about it again, and to defend it if
it is really needed. After all, "it can be abused" applies to pretty much every
API.

Key question is if you _really_ need run-time flag modifications, or if you can
live with initialization-time settings. If you really need it, you'll have to
explain the reasons.

> >On a side note, do you happen to know anyone working on drivers for Si5319 or
> >Si5368 ?
> 
> No.

Too bad ... I may have to write that code myself then.

Thanks,
Guenter
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