In order to implement clock switching for the CLKID_CPU_CLK and
CLKID_CPUB_CLK, notifiers are added on specific points of the
clock tree :
cpu_clk / cpub_clk
| \- cpu_clk_dyn
| | \- cpu_clk_premux0
| | |- cpu_clk_postmux0
| | | |- cpu_clk_dyn0_div
| | | \- xtal/fclk_div2/fclk_div3
| | \- xtal/fclk_div2/fclk_div3
| \- cpu_clk_premux1
| |- cpu_clk_postmux1
| | |- cpu_clk_dyn1_div
| | \- xtal/fclk_div2/fclk_div3
| \- xtal/fclk_div2/fclk_div3
\ sys_pll / sys1_pll
This for each cluster, a single one for G12A, two for G12B.
Each cpu_clk_premux1 tree is marked as read-only and CLK_SET_RATE_NO_REPARENT,
to be used as "parking" clock in a safe clock frequency.
A notifier is added on each cpu_clk_premux0 to detech when CCF want to
change the frequency of the cpu_clk_dyn tree.
In this notifier, the cpu_clk_premux1 tree is configured to use the xtal
clock and then the cpu_clk_dyn is switch to cpu_clk_premux1 while CCF
updates the cpu_clk_premux0 tree.
A notifier is added on each sys_pll/sys1_pll to detect when CCF wants to
change the PLL clock source of the cpu_clk.
In this notifier, the cpu_clk is switched to cpu_clk_dyn while CCF
updates the sys_pll/sys1_pll frequency.
A third small notifier is added on each cpu_clk / cpub_clk and cpu_clk_dyn,
add a small delay at PRE_RATE_CHANGE/POST_RATE_CHANGE to let the other
notofiers change propagate before changing the cpu_clk_premux0 and sys_pll
clock trees.
This notifier set permits switching the cpu_clk / cpub_clk without any
glitches and using a safe parking clock while switching between sub-GHz
clocks using the cpu_clk_dyn tree.
This setup has been tested and validated on the Amlogic G12A and G12B
SoCs running the arm64 cpuburn at [1] and cycling between all the possible
cpufreq translations of each cluster and checking the final frequency using
the clock-measurer, script at [2].
[1] https://github.com/ssvb/cpuburn-arm/blob/master/cpuburn-a53.S
[2] https://gist.github.com/superna9999/d4de964dbc0f84b7d527e1df2ddea25f
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
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