[PATCH 1/2] clk: rename clk_core_get_boundaries() to clk_hw_get_boundaries() and expose
Alexander Kochetkov
al.kochet at gmail.com
Thu Dec 28 04:41:20 PST 2017
Initial thread here:
https://www.spinics.net/lists/linux-clk/msg21682.html
> 27 дек. 2017 г., в 4:06, Stephen Boyd <sboyd at codeaurora.org> написал(а):
>
> Are these limits the min/max limits that the parent clk can
> output at? Or the min/max limits that software has constrained on
> the clk?
>
Don’t know how to answer. For example, parent can output 768MHz,
but some IP work unstable with that parent rate. This issues was observed by
me and I didn’t get official confirmation from rockchip. So, I limit
such clock to 192MHz using clk_set_max_rate(). May be I have to limit clk rate
using another approach.
Anybody from rockchip can confirm that? Or may be contact me clarifying details?
> I haven't looked in detail at this
> rockchip_fractional_approximation() code, but it shouldn't be
> doing the work of both the child rate determination and the
> parent rate determination in one place. It should work with the
> parent to figure out the rate the parent can provide and then
> figure out how to achieve the desired rate from there.
Here is clock tree:
clock rate
----- ----
xin24m 24000000
pll_gpll 768000000
gpll 768000000
i2s_src 768000000
i2s0_pre 192000000
i2s0_frac 16384000
sclk_i2s0 16384000
I limit i2s0_pre rate to 192MHz in order to I2S IP work properly.
rockchip_fractional_approximation() get called for i2s0_frac.
if i2s0_pre rate is 20x times less than i2s0_frac, than rockchip_fractional_approximation()
tries to set i2s0_pre rate to i2s_src rate. It tries to increase it’s parent rate in order
to maximise relation between nominator and denominator.
If I convert rockchip_fractional_approximation() to rockchip_determine_rate(), than I get
min=0, max=192MHz limits inside rockchip_determine_rate(). May be there should be
new logic inside clk framework based on some new clk flags, that will provide max=768MHz
for rockchip_determine_rate().
Also found, that rockchip_fractional_approximation() increase parents rate unconditionally
without taking into account CLK_SET_RATE_PARENT flag.
Stephen, thanks a lot for deep description of determine_rate() background. I’ll taking some
time thinking about possible solutions.
Regards,
Alexander.
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