* Nishanth Menon <nm@xxxxxx> [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@xxxxxx> > 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@xxxxxxxxxxx: co-developed] > Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx> > Signed-off-by: Nishanth Menon <nm@xxxxxx> > --- > .../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@xxxxxxxxxxx> > + * > + * 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 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
