Question about fixed-clock

Question about fixed-clock

[Daniel Mack]

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?


Thanks for a pointer,
Daniel

Re: Question about fixed-clock

[Daniel Mack]

On Tue, Feb 19, 2013 at 12:55 AM, 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>;

Sorry - this is actually <0>.

Re: Question about fixed-clock

[Fabio Estevam]

Hi Daniel,

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.

Re: Question about fixed-clock

[Daniel Mack]

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.


Thanks,
Daniel

Re: Question about fixed-clock

[Daniel Mack]

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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


[-- Attachment #2: 0001-ARM-OMAP-generic-add-call-to-of_clk_init.patch --]
[-- Type: text/x-patch, Size: 1336 bytes --]

>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

Re: Question about fixed-clock

[Daniel Mack]

Hi eyerone,

On 19.02.2013 18:32, Daniel Mack wrote:
> 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
> 
> 
> 0001-ARM-OMAP-generic-add-call-to-of_clk_init.patch
> 
> 
> 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

Any opinion about this approach?


Thanks,
Daniel

Re: Question about fixed-clock

[Afzal Mohammed]

Hi Daniel,

On Tue, Feb 19, 2013 at 09:09:31AM +0530, Afzal Mohammed wrote:

> Hope invoking of_clk_init before clock generator driver helps

Mails coming from this id are in my personal capacity.

On Tue, Feb 19, 2013 at 10:53:18AM +0100, Daniel Mack wrote:
> On 19.02.2013 02:33, Fabio Estevam wrote:

> > Have you registered it with clk_register_fixed_rate() ?

> 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.

Initially didn't realize that it was for an am335x based one.

I feel that for a platform having it's clock tree in DT, of_clk_init
would take care of it, but if clock tree data is not in DT, clock
tree would have to be extended in a non-DT way.

Regards
Afzal

Re: Question about fixed-clock

[Daniel Mack]

Hi Afzal,

thanks for looking into this.

On 07.03.2013 19:42, Afzal Mohammed wrote:
> On Tue, Feb 19, 2013 at 09:09:31AM +0530, Afzal Mohammed wrote:
> 
>> Hope invoking of_clk_init before clock generator driver helps
> 
> Mails coming from this id are in my personal capacity.
> 
> On Tue, Feb 19, 2013 at 10:53:18AM +0100, Daniel Mack wrote:
>> On 19.02.2013 02:33, Fabio Estevam wrote:
> 
>>> Have you registered it with clk_register_fixed_rate() ?
> 
>> 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.
> 
> Initially didn't realize that it was for an am335x based one.
> 
> I feel that for a platform having it's clock tree in DT, of_clk_init
> would take care of it, but if clock tree data is not in DT, clock
> tree would have to be extended in a non-DT way.

Hmm, I don't follow. So for generic OMAP board in general which does
*not* have its SoC clocks in DT, the question is who's in charge of
registering out-of-SoC fixed clocks that are defined in DT.

Note that the clock I'm dealing with here is _outside_ of the SoC, and I
just need to have it in DT, so it can feed another clock chip's input pin.

Grep'ing through arch/arm, it seems that the imx arch does the same
thing my patch does, but I could also imagine that it should be done
somewhere from the DT core. I copied Grant, Rob and Mark for more comments.


Thanks,
Daniel

Re: Question about fixed-clock

[Mark Brown]

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On Thu, Mar 07, 2013 at 11:31:59PM +0100, Daniel Mack wrote:
> On 07.03.2013 19:42, Afzal Mohammed wrote:

> > I feel that for a platform having it's clock tree in DT, of_clk_init
> > would take care of it, but if clock tree data is not in DT, clock
> > tree would have to be extended in a non-DT way.

> Hmm, I don't follow. So for generic OMAP board in general which does
> *not* have its SoC clocks in DT, the question is who's in charge of
> registering out-of-SoC fixed clocks that are defined in DT.

> Note that the clock I'm dealing with here is _outside_ of the SoC, and I
> just need to have it in DT, so it can feed another clock chip's input pin.

> Grep'ing through arch/arm, it seems that the imx arch does the same
> thing my patch does, but I could also imagine that it should be done
> somewhere from the DT core. I copied Grant, Rob and Mark for more comments.

Wouldn't this just be set up by the DT in the same way that other
off-SoC hardware is?

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Re: Question about fixed-clock

[Daniel Mack]

On 08.03.2013 03:15, Mark Brown wrote:
> On Thu, Mar 07, 2013 at 11:31:59PM +0100, Daniel Mack wrote:
>> On 07.03.2013 19:42, Afzal Mohammed wrote:
> 
>>> I feel that for a platform having it's clock tree in DT, of_clk_init
>>> would take care of it, but if clock tree data is not in DT, clock
>>> tree would have to be extended in a non-DT way.
> 
>> Hmm, I don't follow. So for generic OMAP board in general which does
>> *not* have its SoC clocks in DT, the question is who's in charge of
>> registering out-of-SoC fixed clocks that are defined in DT.
> 
>> Note that the clock I'm dealing with here is _outside_ of the SoC, and I
>> just need to have it in DT, so it can feed another clock chip's input pin.
> 
>> Grep'ing through arch/arm, it seems that the imx arch does the same
>> thing my patch does, but I could also imagine that it should be done
>> somewhere from the DT core. I copied Grant, Rob and Mark for more comments.
> 
> Wouldn't this just be set up by the DT in the same way that other
> off-SoC hardware is?

Well,  I thought so too. To repeat, in my DT, I have:

	ref25: ref25M {
		compatible = "fixed-clock";
		#clock-cells = <0>;
		clock-frequency = <25000000>;
	};

to represent an osciallator on the board. I need to specify it here so I
can pass a reference to another chip:

	si5351a: clock-generator@60 {
		compatible = "silabs,si5351a";
		clocks = <&ref25>;
	};

I would have expected that "fixed-clock" is matched by a driver lurking
around for DT boards, just like what the "fixed-regulator" driver does
for instance. But the clock device isn't initialized unless board code
explicitly calls of_clk_init() with a table mentioning "fixed-clock", as
in my patch.

I don't know the clock framework well enough, but it seems that either
all DT boards are supposed to do the same in their generic bits (which
sounds like a lot of code duplication), or the fixed-clock driver should
behave like any other driver wrt its probing from DT. I'm open to
suggestions :)


Daniel

Re: Question about fixed-clock

[Sebastian Hesselbarth]

On 03/08/2013 02:30 PM, Daniel Mack wrote:
> On 08.03.2013 03:15, Mark Brown wrote:
>> On Thu, Mar 07, 2013 at 11:31:59PM +0100, Daniel Mack wrote:
>>> On 07.03.2013 19:42, Afzal Mohammed wrote:
>>> Grep'ing through arch/arm, it seems that the imx arch does the same
>>> thing my patch does, but I could also imagine that it should be done
>>> somewhere from the DT core. I copied Grant, Rob and Mark for more comments.
>>
>> Wouldn't this just be set up by the DT in the same way that other
>> off-SoC hardware is?
 >
 > [...]
>
> I don't know the clock framework well enough, but it seems that either
> all DT boards are supposed to do the same in their generic bits (which
> sounds like a lot of code duplication), or the fixed-clock driver should
> behave like any other driver wrt its probing from DT. I'm open to
> suggestions :)

Daniel,

the current common clock framework does not register any of its "core"
clocks, i.e. fixed-clock, et.al. I haven't had a look at the way regulator
api registers them. But if you find the way reasonable, why not propose
a patch for ccf that registers at least a set of the core clocks itself?

Sebastian

Re: Question about fixed-clock

[Mark Brown]

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On Fri, Mar 08, 2013 at 02:30:27PM +0100, Daniel Mack wrote:
> On 08.03.2013 03:15, Mark Brown wrote:

> > Wouldn't this just be set up by the DT in the same way that other
> > off-SoC hardware is?

> Well,  I thought so too. To repeat, in my DT, I have:

OK, I got CCed in part way through the thread.

> I would have expected that "fixed-clock" is matched by a driver lurking
> around for DT boards, just like what the "fixed-regulator" driver does
> for instance. But the clock device isn't initialized unless board code
> explicitly calls of_clk_init() with a table mentioning "fixed-clock", as
> in my patch.

> I don't know the clock framework well enough, but it seems that either
> all DT boards are supposed to do the same in their generic bits (which
> sounds like a lot of code duplication), or the fixed-clock driver should
> behave like any other driver wrt its probing from DT. I'm open to
> suggestions :)

Your expectation sounds like what I'd expect too...

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Re: Question about fixed-clock

[Afzal Mohammed]

Hi Daniel,

On Tue, Feb 19, 2013 at 12:55:52AM +0100, Daniel Mack wrote:

> 	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.

Hope invoking of_clk_init before clock generator driver helps

Regards
Afzal