Re: [PATCH v2] clk: rockchip: undo several noc and special clocks as critical on rk3288

[Doug Anderson]

Elaine,

On Fri, Apr 12, 2019 at 9:18 AM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> This is mostly a revert of commit 55bb6a633c33 ("clk: rockchip: mark
> noc and some special clk as critical on rk3288") except that we're
> keeping "pmu_hclk_otg0" as critical still.
>
> NOTE: turning these clocks off doesn't seem to do a whole lot in terms
> of power savings (checking the power on the logic rail).  It appears
> to save maybe 1-2mW.  ...but still it seems like we should turn the
> clocks off if they aren't needed.
>
> About "pmu_hclk_otg0" (the one clock from the original commit we're
> still keeping critical) from an email thread:
>
> > pmu ahb clock
> >
> > Function: Clock to pmu module when hibernation and/or ADP is
> > enabled. Must be greater than or equal to 30 MHz.
> >
> > If the SOC design does not support hibernation/ADP function, only have
> > hclk_otg, this clk can be switched according to the usage of otg.
> > If the SOC design support hibernation/ADP, has two clocks, hclk_otg and
> > pmu_hclk_otg0.
> > Hclk_otg belongs to the closed part of otg logic, which can be switched
> > according to the use of otg.
> >
> > pmu_hclk_otg0 belongs to the always on part.
> >
> > As for whether pmu_hclk_otg0 can be turned off when otg is not in use,
> > we have not tested. IC suggest make pmu_hclk_otg0 always on.
>
> For the rest of the clocks:
>
> atclk: No documentation about this clock other than that it goes to
> the CPU.  CPU functions fine without it on.  Maybe needed for JTAG?
>
> jtag: Presumably this clock is only needed if you're debugging with
> JTAG.  It doesn't seem like it makes sense to waste power for every
> rk3288 user.  In any case to do JTAG you'd need private patches to
> adjust the pinctrl the mux the JTAG out anyway.
>
> pclk_dbg, pclk_core_niu: On veyron Chromebooks we turn these two
> clocks on only during kernel panics in order to access some coresight
> registers.  Since nothing in the upstream kernel does this we should
> be able to leave them off safely.  Maybe also needed for JTAG?
>
> hsicphy12m_xin12m: There is no indication of why this clock would need
> to be turned on for boards that don't use HSIC.
>
> pclk_ddrupctl[0-1], pclk_publ0[0-1]: On veyron Chromebooks we turn
> these 4 clocks on only when doing DDR transitions and they are off
> otherwise.  I see no reason why they'd need to be on in the upstream
> kernel which doesn't support DDRFreq.
>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
>
> Changes in v2:
> - Now keep pmu_hclk_otg0 as critical.
> - Updated description since this isn't a clean revert.
> - PWM patches have landed, so just one patch in the series now.
>
>  drivers/clk/rockchip/clk-rk3288.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)

>From previous discussions I think you're all happy with this patch
now, right?  Care to give it an official Reviewed-by tag?

-Doug