Re: [GIT PULL 4/8] clk: tegra: Changes for v4.2-rc1

[Stephen Boyd <sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 05/13, Thierry Reding wrote:
> Hi Mike, Stephen,
> 
> The following changes since commit b787f68c36d49bb1d9236f403813641efa74a031:
> 
>   Linux 4.1-rc1 (2015-04-26 17:59:10 -0700)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/tegra/linux.git tags/tegra-for-4.2-clk
> 
> for you to fetch changes up to 36b7be6d3ea8f434f1e0723f3fb0e85c3e00ebc2:
> 
>   clk: tegra: Fix hda2codec_2x clock name for Tegra30 (2015-05-13 15:17:14 +0200)
> 
> I've based this pull request on top of the tegra-for-4.2-ramcode pull
> request, so pulling only this one should be sufficient to resolve the
> dependency.
> 
> Thanks,
> Thierry
> 
> ----------------------------------------------------------------
> clk: tegra: Changes for v4.2-rc1
> 
> This contains the EMC clock driver that's been exhaustively reviewed and
> tested. It also includes a change to the clock core that allows a clock
> provider to perform low-level reparenting of clocks. This is required by
> the EMC clock driver because the reparenting needs to be done at a very
> specific point in time during the EMC frequency switch.

Can someone please describe why we need to do software
reparenting at a specific point in time during a frequency
switch? I must have missed out on the conversation somewhere and
looking at the commit that introduces the function, the argument
for why the API is exposed:

      To be used by clock implementations for switching to a new
      parent during rate change.

is lacking in any details about *why* we need it.

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