linux-kernel - Re: [PATCH] clk: mmp2: avoid disabling the SP clock when unused

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Date:   Wed, 16 Jan 2019 15:29:47 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Lubomir Rintel <lkundrak@...sk>,
        Michael Turquette <mturquette@...libre.com>
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] clk: mmp2: avoid disabling the SP clock when unused

Quoting Lubomir Rintel (2019-01-16 09:26:31)
> On Wed, 2019-01-16 at 08:37 -0800, Stephen Boyd wrote:
> > Quoting Lubomir Rintel (2019-01-16 01:35:05)
> > > There could be vital functionality running on the SP PJ1 core it can not be
> > > restarted just by turning the clock back on.
> > > 
> > > On the OLPC laptop, the keyboard controller code runs there. It
> > > wouldn't be possible to load the driver for it as a module if the clock
> > > is disabled on boot.
> > > 
> > > Cc: stable@...r.kernel.org # v4.18+
> > > Fixes: commit fc27c2394d96 ("clk: mmp2: add SP clock")
> > > Signed-off-by: Lubomir Rintel <lkundrak@...sk>
> > > ---
> > >  drivers/clk/mmp/clk-of-mmp2.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/clk/mmp/clk-of-mmp2.c b/drivers/clk/mmp/clk-of-mmp2.c
> > > index f2a1c9bbaa63..3e33f1295f59 100644
> > > --- a/drivers/clk/mmp/clk-of-mmp2.c
> > > +++ b/drivers/clk/mmp/clk-of-mmp2.c
> > > @@ -246,7 +246,7 @@ static struct mmp_param_gate_clk apmu_gate_clks[] = {
> > >         {MMP2_CLK_CCIC1, "ccic1_clk", "ccic1_mix_clk", CLK_SET_RATE_PARENT, APMU_CCIC1, 0x1b, 0x1b, 0x0, 0, &ccic1_lock},
> > >         {MMP2_CLK_CCIC1_PHY, "ccic1_phy_clk", "ccic1_mix_clk", CLK_SET_RATE_PARENT, APMU_CCIC1, 0x24, 0x24, 0x0, 0, &ccic1_lock},
> > >         {MMP2_CLK_CCIC1_SPHY, "ccic1_sphy_clk", "ccic1_sphy_div", CLK_SET_RATE_PARENT, APMU_CCIC1, 0x300, 0x300, 0x0, 0, &ccic1_lock},
> > > -       {MMP2_CLK_SP, "sp_clk", NULL, CLK_SET_RATE_PARENT, APMU_SP, 0x1b, 0x1b, 0x0, 0, &sp_lock},
> > > +       {MMP2_CLK_SP, "sp_clk", NULL, CLK_SET_RATE_PARENT | CLK_IGNORE_UNUSED, APMU_SP, 0x1b, 0x1b, 0x0, 0, &sp_lock},
> > 
> > Is it a critical clk that should never be turned off?
> 
> I don't think it is. It is entirely plausible to have no use for the
> "security processor", and in that case it's just okay to keep the clock
> disabled.

So does the firmware/bootloader leave the clk enabled out of boot and we
shouldn't really touch the on/off bits of the clk hardware from the
kernel? Or do we want to actively manage this clk from a driver
somewhere in the kernel?