[PATCH 2/2] clk: bcm2835: expose current divider, parent and mash via debugfs

Eric Anholt eric at anholt.net
Mon Feb 29 15:13:00 PST 2016

Martin Sperl <kernel at martin.sperl.org> writes:

>> On 29.02.2016, at 21:43, Eric Anholt <eric at anholt.net> wrote:
>> kernel at martin.sperl.org writes:
>>> From: Martin Sperl <kernel at martin.sperl.org>
>>> For each clock expose the following values via debugfs:
>>> * current_parent - the currently selected parent
>>> * current_divi - the integer portion of the currently set divider
>>> * current_divf - the fractional portion of the currently set divider
>>> * current_frac - the current frac/mash settings for the divider
>> current_parent can already be found through /debug/clk/clk_summary quite
>> nicely I think.  If we wanted a per-clock parent file, that seems like
>> something the core ought to be doing.
>> current_frac is looking at a bit that doesn't exist for non-MASH clocks.
>> divi/divf are OK, I guess, but don't seem particularly useful given the
>> raw register output already.  A cooked floating point point divider
>> debugfs entry would be nice, but I don't know if we can do that.
> The reason I had those is because I wanted to allow people to
> see quickly what is the parent clock and what is the used 
> parent and divider…
> While discussing with the PCM/I2s people they were always concerned
> about those details - so I needed to provide them with a way to access
> those things easily. And explaining to them the register format was -
> for me - out of the question.
> Especially the mapping of “id” to real parent was a bit of a pain.
> What do you mean by cooked? Something like: "33+27/4096”?

I mean, given your "33+27/4096" example, "33.006591796875"
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