Am Sonntag, 11. Oktober 2015, 12:41:09 schrieb Heiko St?bner:

Hi Stephen,

Am Donnerstag, 8. Oktober 2015, 14:58:40 schrieb Stephen Boyd:

quoted

On 10/02, Heiko St?bner wrote:

quoted

Hi,

any comment on these 3 patches?

Dong has a similar problem, but those patches conflate this with
enabling parent clocks during clk_disable_unused() which makes no
sense to me. So I'm ok with the requirement that we turn clocks
on to change rates, but I wonder if in this case we need to turn
on the clock that's changing rates itself, or if we just need to
turn on the parent and/or future parent of the clock during the
rate switch. Care to elaborate on that?

As you can see in the follow-up patches, the fractional dividers on Rockchip
SoCs are quite strange in that they even need to have their _downstream_
mux point to them to actually accept rate changes.

The register value always reflects the value set by the system, but hardware
really only accepts it if the clock is enabled and even the downstream mux
selects the fractional divider as parent (they call it a auto-gating
feature).

So in the worst (and current) case, you end up with the register showing the
right value, but the hardware can use completely different dividers from
the previous setting.

That strange behaviour got quite deeply investigated between Rockchip and
Google engineers who stumbled upon this in the first place, so I'm
reasonably sure this is the right solution for that clock type :-) .

Xing Zheng now also independently stumbled upon this issue with his rk3036 
work. And came to the same conclusion that the gate must be enabled as well as 
the downstream mux be set to the fractional divider for it to actually accept 
a new setting.