[alsa-devel] [PATCH 15/27] ALSA: hda - Use timecounter_initialize interface

[Pierre-Louis Bossart]

On 1/2/18 12:21 PM, Richard Cochran wrote:
> On Tue, Jan 02, 2018 at 11:15:45AM -0600, Pierre-Louis Bossart wrote:
>> I wrote the code for HDaudio and I remember wasting time trying to figure
>> out the gory details of the cycle counter stuff when all I wanted was a
>> conversion from a 24MHz counter to ns values using a 125/3 operation in the
>> right order - as explained in the comments
> 
> Would using clocks_calc_mult_shift() work for you?

In theory yes, but I'd need to re-check what the results would be.
I remember applying the 1/3 factor separately to avoid wrap-around after 
4 hours [1], but I can't remember the details on the analysis. I can't 
figure out what the 'maxsec' argument should be either.

[1] 
http://elixir.free-electrons.com/linux/latest/source/sound/hda/hdac_stream.c#L486