[PATCH v3 00/10] clk: implement clock rate protection mechanism

[sboyd@codeaurora.org (Stephen Boyd)]

On 06/21, Jerome Brunet wrote:
> 
> I managed to have a run on kci - based on v4.12-rc6:
> https://kernelci.org/boot/all/job/khilman/branch/to-build/kernel/v4.12-rc6-10-ge
> a373ddef830/
> 
> There was no build regression but kci did find one boot regression on qcom
> platforms:
> * qcom-apq8064-cm-qs600
> * qcom-apq8064-ifc6410
> 
> it seems the problem is coming from the clock used by the mmc driver
> (drivers/mmc/host/mmci.c)
> 
> the driver does following sequence:
> * get_clk
> * prepare_enable
> * get_rate
> * set_rate
> * ...
> 
> with clock SDCx_clk (qcom_apq8064.dtsi:1037). This clock has CLK_SET_RATE_PARENT
> flag so it will transmit the request to its parent.
> The parent of this clock is SDCx_src which has the CLK_SET_RATE_GATE flag.
> 
> This can't work with sequence above. The flag was clearly bypassed before, so I
> think it would be best to remove CLK_SET_RATE_GATE from the SDCx_src clocks
> 
> Stephen, would you agree ?
> 
> There was an issue with the chip board as well but this particular board has not
> been very reliable in this lab lately. It has failed on several other job.
> 

Yes the flag was never working before and we've been ignoring the
subtle problems that it causes to change the rate while the clk
is enabled. On these older SoCs, all the clks marked with
CLK_SET_RATE_GATE need to implement something to forcibly disable
all child clks across the rate change. That is the hardware
recommended procedure.

So something like

	get_clk
	prepare_enable
	get_rate
	set_rate
	 call ->set_rate() op
	 forcibly disable children of rcgs
	 actually change the rate of rcg
	 forcibly enable all children that were disabled

and have that happen under one big spinlock local to the qcom
driver I suppose so that enable/disable can't leak into the rate
change. Fun! I'll make an attempt at implementing the right
solution tomorrow/tonight. Of course, we can remove the flag from
qcom drivers if it's blocking this series.

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