Quoting James Liao (2016-01-13 21:55:17)
> Hi Mike,
>
> On Wed, 2016-01-13 at 18:26 -0800, Michael Turquette wrote:
> > Hi James,
> >
> > Quoting James Liao (2016-01-10 19:28:56)
> > > Some modules may need to change its clock rate before turn on it.
> > > So changing PLL's rate when it is off should be allowed.
> > > This patch removes PLL enabled check before set rate, so that
> > > PLLs can set new frequency even if they are off.
> > >
> > > On MT8173 for example, ARMPLL's enable bit can be controlled by
> > > other HW. That means ARMPLL may be turned on even if we (CPU / SW)
> > > set ARMPLL's enable bit as 0. In this case, SW may want and can
> > > still change ARMPLL's rate by changing its pcw and postdiv settings.
> > > But without this patch, new pcw setting will not be applied because
> > > its enable bit is 0.
> >
> > Must the clock signal be enabled to change the PLL rate? If so, does
> > ARMPLL set the CLK_SET_RATE_GATE flag?
>
> No. The controlling of PLL's rate and enable are independent. So we can
> change the PLL's rate when it's enabled or disabled.
Thanks for the clarification.
>
> > >
> > > Signed-off-by: James Liao <jamesjj.liao at mediatek.com>
> > > ---
> > > drivers/clk/mediatek/clk-pll.c | 9 ++-------
> > > 1 file changed, 2 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/clk/mediatek/clk-pll.c b/drivers/clk/mediatek/clk-pll.c
> > > index 966cab1..8e31fae 100644
> > > --- a/drivers/clk/mediatek/clk-pll.c
> > > +++ b/drivers/clk/mediatek/clk-pll.c
> > > @@ -91,9 +91,6 @@ static void mtk_pll_set_rate_regs(struct mtk_clk_pll *pll, u32 pcw,
> > > int postdiv)
> > > {
> > > u32 con1, val;
> > > - int pll_en;
> > > -
> > > - pll_en = readl(pll->base_addr + REG_CON0) & CON0_BASE_EN;
> > >
> > > /* set postdiv */
> > > val = readl(pll->pd_addr);
> > > @@ -114,15 +111,13 @@ static void mtk_pll_set_rate_regs(struct mtk_clk_pll *pll, u32 pcw,
> > >
> > > con1 = readl(pll->base_addr + REG_CON1);
> > >
> > > - if (pll_en)
> > > - con1 |= CON0_PCW_CHG;
> > > + con1 |= CON0_PCW_CHG;
> >
> > This unconditionally enables the PLL whenever clk_set_rate is called,
> > changing the previous behavior. The clk framework still tracks the
> > intent of ARMPLLs users with the enable_count. How about something like
> > the following:
>
> Not really. This patch will not enable or disable PLL when we change its
> rate. The PLL enable bit is bit[0], we didn't change bit[0] in
> mtk_pll_set_rate_regs(), so its state will not be changed.
>
> This patch set CON0_PCW_CHG (bit[31]) no matter the PLL is enabled or
> not. So we don't need to check the enable bit[0] nor PLL state in the
> framework before set bit[31].
Ah, I mistakenly thought that CON0_PCW_CHG was the enable bit, since
setting it was guarded by the pll_en conditional. Your explanation makes
perfect sense to me.
Acked-by: Michael Turquette <mturuqette at baylibre.com>
Regards,
Mike
>
> > bool pll_en = clk_hw_is_enabled(&pll->hw);
> >
> > if (pll_en)
> > con1 |= CON0_PCW_CHG;
> >
> > writel(con1, pll->base_addr + REG_CON1);
> > if (pll->tuner_addr)
> > writel(con1 + 1, pll->tuner_addr);
> >
> > if (pll_en)
> > udelay(20);
> >
> > This does not rely on the hardware to tell us the intent of the user,
> > but instead on our framework usecounting.
>
>
> Best regards,
>
> James
>
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