[RFC][PATCH 1/2] ARM: OMAP4: clock: Add device tree support for AUXCLKs
Tony Lindgren
tony at atomide.com
Wed Apr 10 14:49:20 EDT 2013
* Nishanth Menon <nm at ti.com> [130410 10:44]:
> Details in the patch below (Tony, I have added you as collaborator for
> helping in getting this working-clk_add_alias was'nt needed in the
> internal patch discussion we had - I have taken a bit of freedom in
> adding your contributions to the patch below)
OK thanks. Noticed few minor things, see below.
> Folks, this does seem to be the best compromise we can achieve at this
> point in time. feedback on this approach is much appreciated - if folks
> are ok, I can post this as an formal patch series.
>
> From 130a41821bf57081ca45ef654029175d173135e6 Mon Sep 17 00:00:00 2001
> From: Nishanth Menon <nm at ti.com>
> Date: Tue, 9 Apr 2013 19:26:40 -0500
> Subject: [RFC PATCH] 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. There are many possible approaches to this
> problem as discussed in the following thread:
> http://marc.info/?t=136370325600009&r=1&w=2
It might be worth clarifying that this is especially for the board
specific clocks initially. The fixed clocks are currently found via
the clock aliases table.
> 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 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>, kernel updates 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 and warning.
>
> Even though we can 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: an 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.
>
> [tony at atomide.com: co-developed]
> Signed-off-by: Tony Lindgren <tony at atomide.com>
> Signed-off-by: Nishanth Menon <nm at ti.com>
> ---
> .../devicetree/bindings/clock/omap-clock.txt | 40 +++++++++
> drivers/clk/Makefile | 1 +
> drivers/clk/omap/Makefile | 1 +
> drivers/clk/omap/clk.c | 94 ++++++++++++++++++++
> 4 files changed, 136 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
>
> diff --git a/Documentation/devicetree/bindings/clock/omap-clock.txt b/Documentation/devicetree/bindings/clock/omap-clock.txt
> new file mode 100644
> index 0000000..07e3ff8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/omap-clock.txt
> @@ -0,0 +1,40 @@
> +Device Tree Clock bindings for Texas Instrument's OMAP compatible platforms
> +
> +This binding is a work-in-progress, and meant to be stage #1 of transitioning
> +OMAP clock data out of kernel image.
As it's using the common clock binding, this will be supported in the
long run too. So maybe replace work-in-progress with initial minimal
binding that can be enhanced later on.
> +This binding uses the common clock binding[1].
> +
> +[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
> +
> +Required properties:
> +- compatible : shall be "ti,omap-clock"
> +- #clock-cells : from common clock binding; shall be set to 0.
> +NOTE:
> +node name should map to clock database in arch/arm/mach-omap2/cclock<SoC>_data.c
> +Since all clocks are described with _ck, the node name is optimized to drop the
> +usage of _ck. For example, a clock called dpll1_ck will be defined as dpll1.
> +
> +Example #1: describing clock node for CPU on OMAP34xx platform:
> +Ref: arch/arm/mach-omap2/cclock3xxx_data.c
> +describes the CPU clock to be as follows
> + CLK(NULL, "dpll1_ck", &dpll1_ck, CK_3XXX),
> +Corresponding binding will be:
> + dpll1: dpll1 {
> + #clock-cells = <0>;
> + compatible = "ti,omap-clock";
> + };
> +And it's usage will be:
> + clocks = <&dpll1>;
> +
> +Example #2: describing clock node for auxilary clock #3 on OMAP443x platform:
> +Ref: arch/arm/mach-omap2/cclock44xx_data.c
> +describes the auxclk3 clock to be as follows:
> + CLK(NULL, "auxclk3_ck", &auxclk3_ck, CK_443X),
> +Corresponding binding will be:
> + auxclk3: auxclk3 {
> + #clock-cells = <1>;
> + compatible = "ti,omap-clock";
> + };
> +And it's usage will be:
> + clocks = <&auxclk3>;
The #clock-cells in the auxclk3 example should also be 0 instead of 1
AFAIK. We should only use #clock-cells = <1> when the same physical
clock provides multiple outputs. I believe the auxclocks are all separate,
but that needs to be verified.
> diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> index 300d477..a0209d7 100644
> --- a/drivers/clk/Makefile
> +++ b/drivers/clk/Makefile
> @@ -27,6 +27,7 @@ obj-$(CONFIG_ARCH_U8500) += ux500/
> obj-$(CONFIG_ARCH_VT8500) += clk-vt8500.o
> obj-$(CONFIG_ARCH_ZYNQ) += clk-zynq.o
> obj-$(CONFIG_ARCH_TEGRA) += tegra/
> +obj-$(CONFIG_ARCH_OMAP) += omap/
>
> obj-$(CONFIG_X86) += x86/
>
> diff --git a/drivers/clk/omap/Makefile b/drivers/clk/omap/Makefile
> new file mode 100644
> index 0000000..8195931
> --- /dev/null
> +++ b/drivers/clk/omap/Makefile
> @@ -0,0 +1 @@
> +obj-y += clk.o
> diff --git a/drivers/clk/omap/clk.c b/drivers/clk/omap/clk.c
> new file mode 100644
> index 0000000..63a4cce
> --- /dev/null
> +++ b/drivers/clk/omap/clk.c
> @@ -0,0 +1,94 @@
> +/*
> + * Texas Instruments OMAP Clock driver
> + *
> + * Copyright (C) 2013 Texas Instruments Incorporated - http://www.ti.com/
> + * Nishanth Menon
> + * Tony Lindgren <tony at atomide.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> + * kind, whether express or implied; without even the implied warranty
> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/clkdev.h>
> +#include <linux/clk-private.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/string.h>
> +
> +static const struct of_device_id omap_clk_of_match[] = {
> + {.compatible = "ti,omap-clock",},
> + {},
> +};
> +
> +MODULE_DEVICE_TABLE(of, omap_clk_of_match);
> +
> +/**
> + * omap_clk_probe() - create link from DT definition to clock data
> + * @pdev: device node
> + *
> + * REVISIT: We are now assuming the following:
> + * 1. omap clock names end with _ck
> + * 2. omap clocks don't get removed
> + */
> +static int omap_clk_probe(struct platform_device *pdev)
> +{
> + struct clk *clk;
> + int res;
> +
> + const struct of_device_id *match;
> + struct device_node *np = pdev->dev.of_node;
> + char clk_name[32];
> +
> + match = of_match_device(omap_clk_of_match, &pdev->dev);
> +
> + /* Set up things so consumer can call clk_get() with name */
> + snprintf(clk_name, 32, "%s_ck", np->name);
> + clk = clk_get(NULL, clk_name);
> + if (IS_ERR(clk)) {
> + res = PTR_ERR(clk);
> + dev_err(&pdev->dev, "could not get clock %s (%d)\n",
> + clk_name, res);
> + goto out;
> + }
It seems that at least for now we can assume the naming will stay
that way, then if we need other rules for finding clocks, we can
add omap_match_clock() function or something.
> + /* This allows the driver to of_clk_get() */
> + res = of_clk_add_provider(np, of_clk_src_simple_get, clk);
> + if (res)
> + dev_err(&pdev->dev, "could not add provider for %s (%d)\n",
> + clk_name, res);
> +
> + clk_put(clk);
> +out:
> + return res;
> +}
We can avoid the concern of storing the struct clk * and do the
look up lazily on consumer driver probe by setting a dummy struct
clk * here. Then replace of_clk_src_simple_get() with a custom
omap_clk_src_get() that does the lookup and replaces the struct
clk * with the real one.
> +MODULE_ALIAS("platform:omap_clk");
> +
> +/* We assume here that OMAP clocks will not be removed */
> +static struct platform_driver omap_clk_driver = {
> + .probe = omap_clk_probe,
> + .driver = {
> + .name = "omap_clk",
> + .owner = THIS_MODULE,
> + .of_match_table = of_match_ptr(omap_clk_of_match),
> + },
> +};
> +
> +static int __init omap_clk_init(void)
> +{
> + return platform_driver_register(&omap_clk_driver);
> +}
> +
> +arch_initcall(omap_clk_init);
>
> +MODULE_DESCRIPTION("OMAP Clock driver");
> +MODULE_AUTHOR("Texas Instruments Inc.");
> +MODULE_LICENSE("GPL v2");
Regards,
Tony
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