Messages in this thread Patch in this message | | | Date | Tue, 19 Feb 2013 18:32:09 +0100 | From | Daniel Mack <> | Subject | Re: Question about fixed-clock |
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On 19.02.2013 18:22, Mike Turquette wrote: > Quoting Daniel Mack (2013-02-19 01:53:18) >> Hi Fabio, >> Hi Afzal, >> >> On 19.02.2013 02:33, Fabio Estevam wrote: >>> On Mon, Feb 18, 2013 at 8:55 PM, Daniel Mack <zonque@gmail.com> wrote: >>>> Hi, >>>> >>>> This might be a stupid question, but I'm somehow stuck here. I'm using a >>>> driver with the following DTS sub-node: >>>> >>>> ref25: ref25M { >>>> compatible = "fixed-clock"; >>>> #clock-cells = <0>; >>>> clock-frequency = <25000000>; >>>> }; >>>> >>>> clock-generator@0 { >>>> /* ... */ >>>> #clock-cells = <1>; >>>> clocks = <&ref25>; >>>> } >>>> >>>> The device driver for clock-generator uses something like the following >>>> call to get its clock: >>>> >>>> clk = of_clk_get(np, 0); >>>> >>>> but the return value is ERR_PTR(-ENOENT) and I also can't find this >>>> clock in the clk debugfs tree. >>>> >>>> This is on a OMAP/AM33xx device with kernel 3.8-rc7 plus the -next tips >>>> of arm-soc and omap, but with no other special clock options selected in >>>> the config. Is there anything I'm missing to correctly instantiate the >>>> dummy clock? >>> >>> Have you registered it with clk_register_fixed_rate() ? >>> >>> In imx we use imx_clk_fixed, which in turns call clk_register_fixed_rate(). >>> >>> Take a look at arch/arm/mach-imx/clk-imx51-imx53.c for a reference. >> >> Hmm no, I didn't do anything else than adding it to the DT in the first >> place, hoping that a driver will pick it up and add the clock for me. >> But it turns out that of_clk_init() is not called at all on my platform. >> >> I'm doing this now from omap_generic_init() and it works. If that's an >> appropriate place to call it, I can provide a patch. >> > > You can provide a patch, but your example above is for a dummy clock, > correct?
No, it's a real clock with a fixed frequency on the board, which feeds another clock chip. I thought this is what fixed-clock is for, just like what a fixed-regulator does? Or how would you describe such a thing in DT, in order to use it as input to another device?
> It would be best to post your patch along with a real-world > use for calling of_clk_init().
Not sure what you mean exactly, but the patch is attached. However, I still think I lack some understanding here - the fact that compatible strings have to be passed explicitly from generic code feels wrong.
Thanks, Daniel
From 850120371830ffb5e2146aeb2d21c724d6ded09e Mon Sep 17 00:00:00 2001 From: Daniel Mack <zonque@gmail.com> Date: Tue, 19 Feb 2013 12:05:25 +0100 Subject: [PATCH] ARM: OMAP: generic: add call to of_clk_init()
This is needed to instanciate fixed clocks in the DT.
Signed-off-by: Daniel Mack <zonque@gmail.com> --- arch/arm/mach-omap2/board-generic.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/arch/arm/mach-omap2/board-generic.c b/arch/arm/mach-omap2/board-generic.c index 0274ff7..3580f16 100644 --- a/arch/arm/mach-omap2/board-generic.c +++ b/arch/arm/mach-omap2/board-generic.c @@ -15,6 +15,7 @@ #include <linux/of_irq.h> #include <linux/of_platform.h> #include <linux/irqdomain.h> +#include <linux/clk-provider.h> #include <asm/mach/arch.h> @@ -35,6 +36,11 @@ static struct of_device_id omap_dt_match_table[] __initdata = { { } }; +static const __initconst struct of_device_id clk_match[] = { + { .compatible = "fixed-clock", .data = of_fixed_clk_setup, }, + {} +}; + static void __init omap_generic_init(void) { omap_sdrc_init(NULL, NULL); @@ -49,6 +55,7 @@ static void __init omap_generic_init(void) omap4_panda_display_init_of(); else if (of_machine_is_compatible("ti,omap4-sdp")) omap_4430sdp_display_init_of(); + of_clk_init(clk_match); } #ifdef CONFIG_SOC_OMAP2420 -- 1.8.1.2
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