From: emilio@elopez•com.ar (Emilio López)
To: linux-arm-kernel@lists•infradead.org
Subject: Common clock: function clock and bus clock
Date: Thu, 13 Mar 2014 00:16:35 -0300 [thread overview]
Message-ID: <53212313.9040305@elopez.com.ar> (raw)
In-Reply-To: <CADApbeh0zjd=qMguiqQGrn=0v+-SVqgnyL=Gk8D9MiQvHU2XGA@mail.gmail.com>
Hi,
El mi? 12 mar 2014 23:15:20 ART, Chao Xie escribi?:
> On Wed, Mar 12, 2014 at 6:14 PM, Grygorii Strashko
> <grygorii.strashko@ti•com> wrote:
>> On 03/12/2014 04:30 AM, Chao Xie wrote:
>>>
>>> On Tue, Mar 11, 2014 at 10:48 AM, Haojian Zhuang
>>> <haojian.zhuang@gmail•com> wrote:
>>>>
>>>> On Tue, Mar 11, 2014 at 10:06 AM, Chao Xie <xiechao.mail@gmail•com>
>>>> wrote:
>>>>>
>>>>> hi
>>>>>
>>>>> I can not find any examples for handling function clock and bus clock
>>>>> in drivers/clk/.
>>>>>
>>>>> For a device, it will have a function clock and bus clock. function
>>>>> clock will control the fucntionality of this device, while bus clock
>>>>> will control the communication part to the bus.
>>>>>
>>>>> For some SOCes, they do not export bus clock, so from the hardware it
>>>>> seems that function clock is combined with bus clock, while for some
>>>>> SOCes, they are not.
>>>>>
>>>>> For most of the device driver, they will enable/disable function clock
>>>>> and bus clock both. While for some devices, they may share bus clock,
>>>>> and have different function clocks.
You can define two normal clocks and use them like this
* If a device has both bus and module
clocks = <&abc ...>, <&xyz ...>;
clock-names = "bus", "module";
* If a device only has module clock
clocks = <&xyz ...>;
clock-names = "module";
Then on the driver to control this specific hardware you can do
something like
/* mandatory module clock */
mod = devm_clk_get(dev, "module");
if (!IS_ERR(mod))
clk_prepare_enable(mod)
else
goto fail;
/* optional bus clock */
bus = devm_clk_get(dev, "bus");
if (!IS_ERR(bus))
clk_prepare_enable(bus)
The framework keeps count of how many times clocks have been enabled, so
as long as a device needs the bus clock, it will remain operational.
You can find many examples of this pattern with
$ grep 'clock-names.*ahb' arch/arm/boot/dts/*dts*
Cheers,
Emilio
next prev parent reply other threads:[~2014-03-13 3:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-11 2:06 Common clock: function clock and bus clock Chao Xie
2014-03-11 2:48 ` Haojian Zhuang
2014-03-12 2:30 ` Chao Xie
2014-03-12 10:14 ` Grygorii Strashko
2014-03-13 2:15 ` Chao Xie
2014-03-13 3:16 ` Emilio López [this message]
2014-03-13 11:30 ` Grygorii Strashko
[not found] ` <20140319210428.31449.19420@quantum>
[not found] ` <CAPDyKFqg230Ob5Wxu0tvXqia+B3WG5+YdKTdxTQ0ySbZokb+7Q@mail.gmail.com>
2014-03-20 10:30 ` Grygorii Strashko
2014-03-20 11:42 ` Russell King - ARM Linux
2014-03-20 9:45 ` Ben Dooks
2014-03-20 11:35 ` Russell King - ARM Linux
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