[PATCH v2 2/4] doc: dt: add documentation for lpc1850-cgu clk driver

Joachim Eastwood manabian at gmail.com
Thu May 21 15:21:10 PDT 2015

On 21 May 2015 at 23:17, Michael Turquette <mturquette at linaro.org> wrote:
> Quoting Joachim Eastwood (2015-05-13 00:57:18)
>> On 13 May 2015 at 00:12, Michael Turquette <mturquette at linaro.org> wrote:
>> >
>> > Why do you need to use clock-indices?
>> Since the CGU can have up to 27 clock lines, but in this device not
>> all are used. So I use clock-indices so I don't need to have empty
>> entries in the clock-output-names array. I thought this was the
>> intended usage(?)
>> > Why do you need to use clock-output-names? If all of your clock
>> > consumers have nodes in DT then you can skip this and name them on the
>> > consuming side. See a further explanation here:
>> > http://lkml.kernel.org/r/<20150416192014.19585.9663@quantum>
>> Most of the clocks from the CGU goes to a CCU, but the CCU isn't the
>> real consumer. It's more like a clock router with a bunch of gates.
>> If you take a close look at the CCU driver you will notice that it
>> doesn't do clk_get on any of the clocks. My reason for doing this is
>> to not increase the usage counter on the CGU clock so that if there
>> are no consumer after a CCU the entire clock line up to the CGU can be
>> disabled. So this is the reason that the CCU driver uses a "special"
>> way to grab the clock output names from the CGU.
> A call to clk_get will not enable/ungate the clock signal. It seems that
> there might be some confusion around that. It is always OK to get the
> clk. This will not increase the enable_count or prepare_count values.
> If the CCU is a separate IP block then it might make sense for it to
> call clk_get on the CGU clocks. On the other hand it might make more
> sense for the CCU clocks to simply use the CGU clocks as parent clock
> signal inputs.

v3, that was sent a couple of days ago, uses of_clk_get/clk_get_name
to set the CCU clock parents. See v3 cover letter for a short

> None of the points above have anything to do with my original comment.
> The use of the clock-output-names property is unnecessary if all of the
> consumer devices have DT nodes of their own. Please look at the thread I
> linked to and let me know what you think about getting rid of the
> clock-output-names property.

v3 removes the property. Please take a look at it when you get the time.

Joachim Eastwood

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