Re: Question about fixed-clock

[Daniel Mack <zonque@gmail.com>]

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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


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>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