[PATCH v2] clk: mediatek: Allow changing PLL rate when it is off

[mturquette@baylibre.com (Michael Turquette)]

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@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@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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