[V4,1/6] clk: OMAP: introduce device tree binding to kernel clock data

From: Nishanth Menon <nm@ti.com>

On 10:22-20130413, Tony Lindgren wrote:
> * Nishanth Menon <nm@ti.com> [130412 16:43]:
> > Thanks for checking up. Fixed all of them below, will post part of
> > series again, only if I need to address further comments in other
> > patches..
> 
> Thanks it seems that the other ones are ready to go, just one
> more comment below.
> 
[...]
> > +static struct clk *omap_clk_src_get(struct of_phandle_args *clkspec, void *data)
> > +{
> > +	struct clk *clk;
> > +	char clk_name[32];
> > +	struct device_node *np = clkspec->np;
> > +
> > +	snprintf(clk_name, 32, "%s_ck", np->name);
> > +	clk = clk_get(NULL, clk_name);
> > +	if (IS_ERR(clk)) {
> > +		pr_err("%s: could not get clock %s(%ld)\n", __func__,
> > +		       clk_name, PTR_ERR(clk));
> > +		goto out;
> > +	}
> > +	clk_put(clk);
> 
> It seems that clk_put() is actually wrong here. That's because
> of_clk_get() should boild down to just the look up of the clock 
> and then clk_get() on it, so no double clk_get() is done in this
> case. Once the consumer driver is done, it will just call clk_put()
> on it.
Yep - updated version below.
From d0bf3fce235cff46feac7f5ef1a40e2fa0f2aa12 Mon Sep 17 00:00:00 2001
From: Nishanth Menon <nm@ti.com>
Date: Tue, 9 Apr 2013 19:26:40 -0500
Subject: [PATCH V5.1 1/6] clk: OMAP: introduce device tree binding to kernel clock
 data

OMAP clock data is located in arch/arm/mach-omap2/cclockXYZ_data.c.
However, this presents an obstacle for using these clock nodes in
Device Tree definitions. This is especially true for board specific
clocks initially. The fixed clocks are currently found via clock
aliases table. There are many possible approaches to this problem as
discussed in the following thread:
http://marc.info/?t=136370325600009&r=1&w=2.
Highlights of the options:
a) device specific clk_add_alias:
   cons: driver handling required
b) using an generic clk node and indexing to reach the clock required.
   This is similar in approach taken by tegra and few other platforms.
   Example usage: clock = <&clk 5>;
   cons: potential to have mismatches in indexed table and associated
   dtb data. In addition, managing continued documentation in bindings
   as clock indexing increases. Even though readability angle could be
   improved by using preprocessing of DT using macros, indexed
   approach is inherently risky from cases like the following:
   clk indexes in kernel:
   1 - mpu_dpll
   2 - aux_clk1
   3 - core_clk
   DT entry for peripheral X uses <&clk 2> to reach aux_clk1. Now, let's
   say kernel updates indices to:
   1 - mpu_dpll
   2 - per_dpll
   3 - aux_clk1
   4 - core_clk
   using the old dtb(or dts missing an update), on new kernel which
   has updated indices will result in per_dpll now controlled for
   peripheral X without warning or any potential error detection.

   Even though we could claim this is user error, such errors are hard
   to track down and fix.

An alternate approach introduced here is to introduce device tree
bindings corresponding to the clock nodes required in DT definition
for SoC which automatically maps back to the definitions in
cclockXYZ_data.c.

The driver introduced here to do this mapping will eventually be the
place where the clock handling will migrate to. We need to consider
this angle as well so that the solution will be an valid transition
point for moving the clock data out of kernel image (into device tree
or firmware load etc..).

Overall strategy introduced here is simple: a clock node described in
device tree blob is used to identify the exact clock provided in the
SoC specific data. This is then linked back using of_clk_add_provider
to the device node to be accessible by of_clk_get.

Based on discussion contributions from Roger Quadros, Grygorii Strashko
and others.

Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Paul Walmsley <paul@pwsan.com>
[tony@atomide.com: co-developed]
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
---
 .../devicetree/bindings/clock/omap-clock.txt       |   40 +++++++++
 drivers/clk/Makefile                               |    1 +
 drivers/clk/omap/Makefile                          |    1 +
 drivers/clk/omap/clk.c                             |   91 ++++++++++++++++++++
 4 files changed, 133 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/omap-clock.txt
 create mode 100644 drivers/clk/omap/Makefile
 create mode 100644 drivers/clk/omap/clk.c

[V4,1/6] clk: OMAP: introduce device tree binding to kernel clock data

Commit Message

Comments

Patch