Message-ID: <51666AE8.9060602@ti.com>
Date:	Thu, 11 Apr 2013 10:48:56 +0300
From:	Roger Quadros <rogerq@...com>
To:	Nishanth Menon <nm@...com>
CC:	Mike Turquette <mturquette@...aro.org>,
	Tony Lindgren <tony@...mide.com>, <linux-usb@...r.kernel.org>,
	<linux@....linux.org.uk>, <devicetree-discuss@...ts.ozlabs.org>,
	<linux-kernel@...r.kernel.org>, <balbi@...com>,
	<grygorii.strashko@...com>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC][PATCH 1/2] ARM: OMAP4: clock: Add device tree support for
 AUXCLKs

On 04/10/2013 08:39 PM, Nishanth Menon wrote:
> On 13:55-20130410, Roger Quadros wrote:
>> On 04/10/2013 11:06 AM, Mike Turquette wrote:
>>> Quoting Nishanth Menon (2013-04-09 13:49:00)
>>>> On 10:43-20130409, Tony Lindgren wrote:
>>>>> * Tony Lindgren <tony@...mide.com> [130409 09:54]:
>>>>>> * Roger Quadros <rogerq@...com> [130409 03:00]:
>>>>>>> On 04/05/2013 06:58 PM, Tony Lindgren wrote:
>>>>>>>>
>>>>>>>> Can't you just use the clock name there to get it?
>>>>>>>
>>>>>>> In device tree we don't pass around clock names. You can either get
>>>>>>> a phandle or an index to the clock.
>>>>>>>
>>>>>>> e.g. Documentation/devicetree/bindings/clock/imx31-clock.txt
>>>>>>
>>>>>> Yes I understand that. But the driver/clock/omap driver can just
>>>>>> remap the DT device initially so the board specific clock is
>>>>>> found from the clock alias table. Basically initially a passthrough
>>>>>> driver that can be enhanced to parse DT clock bindings and load
>>>>>> data from /lib/firmware.
>>>>>
>>>>> Actually probably the driver/clock/omap can even do even less
>>>>> initially. There probably even no need to remap clocks there.
>>>>>
>>>>> As long as the DT clock driver understands that a board specific
>>>>> auxclk is specified in the DT it can just call clk_add_alias() so
>>>>> the driver will get the right auxclk from cclock44xx_data.c.
>>>>>
>>>>> Then other features can be added later on like to allocate a
>>>>> clock entirely based on the binding etc.
>>>> I did try to have an implementation for cpufreq using clock nodes.
>>>> unfortunately, device tree wont let me have arguments of strings :(
>>>> So, I am unable to do clock = <&clk mpu_dpll>;
>>>> instead, I am forced to do clock = <&clk 249>;
>>>>
>>>
>>> See http://article.gmane.org/gmane.linux.ports.arm.kernel/229034
>>>
>>
>> Awesome. Thanks for pointing this out Mike.
>>
>> Now all we need to do is create a named define for each clock index in the
>> header file.
> Approach #3: Thanks to Tony for collaborating on this:
> Works for cpufreq-cpu0 - additional patches:
> http://pastebin.com/GHnTRVJf, http://pastebin.com/FZS89J6L (tested on
> beagleXM)
> Work for USB - http://pastebin.com/aJpDnXci - thanks Roger for testing
> this.
> 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)
> 
> 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.

This looks fine to me. Minor comments below.

> 
> From 130a41821bf57081ca45ef654029175d173135e6 Mon Sep 17 00:00:00 2001
> From: Nishanth Menon <nm@...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
> 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

typo: "an"->"a"

> 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@...mide.com: co-developed]
> Signed-off-by: Tony Lindgren <tony@...mide.com>
> Signed-off-by: Nishanth Menon <nm@...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.
> +
> +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>;
> 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

missing e-mail id.

> + *	Tony Lindgren <tony@...mide.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);
> +
Is this driver ever going to be a loadable module? If not then you don't need this.

> +/**
> + * 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;
> +	}
> +
> +	/* 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;
> +}
> +
> +MODULE_ALIAS("platform:omap_clk");

ditto.

> +
> +/* 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,

same here.

> +		   .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");
> 

cheers,
-roger
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