On 03/21/2013 12:46 PM, Martin Fuzzey wrote:

On 21/03/13 17:11, Timur Tabi wrote:

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On Thu, Mar 21, 2013 at 3:39 AM, Martin Fuzzey mfuzzey@parkeon.com wrote:

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With this patch and that DT example the frequency of clock 162 will be _set_ to 20MHz

Does that mean that it ignores the ' clocks' parameter?

No, in this case the clocks parameter must contain the phandle of a clock whose rate is configurable.

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If clock-frequency is omitted the binding is still correct (hence the optional) but the frequency of clock 162 would not be modified.

In the documentation I wrote "If both a clock and clock-frequency are provided the clock's rate will be set. " maybe this is not clear enough? It's not clear what it will be set *to*.

It will be set to the frequency specified by the clock-frquency attribute.

Would "If both a clock and clock-frequency are provided clock must support the set_rate operation and its frequency will be set to the value specified by clock-frequency" be better?

Yes, that's much better.

The possible configurations and their use cases are:

1. only 'clocks' specified

clock points to a clock specified in the DT which already has an appropriate frequency and is configured by some other means external to the sgtl5000 driver (bootloader, board setup code, or just a fixed rate clock)

2. only 'clock-frequency' specified

The chip is assumed to be clocked by a signal having the given frequency, which may even be generated by a clock unknown to linux. This could actually be represented as a special case of 1) by defining a fixed-rate clock in the DT.

3. Both 'clocks' and 'clock-frequency' specified

The chip is assumed to be clocked by a rate programmable clock defined in the clock tree. clk_set_rate() will be called for this clock to set its rate to that specified by clock-frequency

This should all be in the binding document.

Cases 1 and 2 exist in the current code, this patch adds support for case 3.

Prior to commit 81e8e4926167ab32593bbb915b45a42024ca1020 "ASoC: fsl: add sgtl5000 clock support for imx-sgtl5000" only case 2 was supported This explains why 2 is not implemented as a special case of 1) plain 'clock-frequency' was supported before the driver learnt how to get a clock from the DT

And this should be in the patch description.