linux-kernel - Re: [PATCH v2 3/5] clk: mediatek: Fix asymmetrical PLL enable and disable control

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Message-ID: <1597127686.20627.8.camel@mtksdaap41>
Date:   Tue, 11 Aug 2020 14:34:46 +0800
From:   Weiyi Lu <weiyi.lu@...iatek.com>
To:     Nicolas Boichat <drinkcat@...omium.org>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
        James Liao <jamesjj.liao@...iatek.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>, <linux-clk@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Wendell Lin <wendell.lin@...iatek.com>
Subject: Re: [PATCH v2 3/5] clk: mediatek: Fix asymmetrical PLL enable and
 disable control

On Wed, 2020-07-29 at 19:02 +0800, Nicolas Boichat wrote:
> On Wed, Jul 29, 2020 at 6:51 PM Nicolas Boichat <drinkcat@...omium.org> wrote:
> >
> > On Wed, Jul 29, 2020 at 4:44 PM Weiyi Lu <weiyi.lu@...iatek.com> wrote:
> > >
> > > The en_mask actually is a combination of divider enable mask
> > > and pll enable bit(bit0).
> > > Before this patch, we enabled both divider mask and bit0 in prepare(),
> > > but only cleared the bit0 in unprepare().
> > > Now, setting the enable register(CON0) in 2 steps: first divider mask,
> > > then bit0 during prepare(), vice versa.
> > > Hence, en_mask will only be used as divider enable mask.
> > > Meanwhile, all the SoC PLL data are updated.
> >
> > I like this a lot better, most changes look fine, just a few nits.
> >
> > >
> > > Signed-off-by: Weiyi Lu <weiyi.lu@...iatek.com>
> > > ---
> > >  drivers/clk/mediatek/clk-mt2701.c | 26 ++++++++++++------------
> > >  drivers/clk/mediatek/clk-mt2712.c | 30 ++++++++++++++--------------
> > >  drivers/clk/mediatek/clk-mt6765.c | 20 +++++++++----------
> > >  drivers/clk/mediatek/clk-mt6779.c | 24 +++++++++++-----------
> > >  drivers/clk/mediatek/clk-mt6797.c | 20 +++++++++----------
> > >  drivers/clk/mediatek/clk-mt7622.c | 18 ++++++++---------
> > >  drivers/clk/mediatek/clk-mt7629.c | 12 +++++------
> > >  drivers/clk/mediatek/clk-mt8173.c | 42 ++++++++++++++++++++++++++-------------
> > >  drivers/clk/mediatek/clk-mt8183.c | 22 ++++++++++----------
> > >  drivers/clk/mediatek/clk-pll.c    | 10 ++++++++--
> > >  10 files changed, 122 insertions(+), 102 deletions(-)
> > >
> [snip]
> > > diff --git a/drivers/clk/mediatek/clk-pll.c b/drivers/clk/mediatek/clk-pll.c
> > > index f440f2cd..3c79e1a 100644
> > > --- a/drivers/clk/mediatek/clk-pll.c
> > > +++ b/drivers/clk/mediatek/clk-pll.c
> > > @@ -247,8 +247,10 @@ static int mtk_pll_prepare(struct clk_hw *hw)
> > >         writel(r, pll->pwr_addr);
> > >         udelay(1);
> > >
> > > -       r = readl(pll->base_addr + REG_CON0);
> > > -       r |= pll->data->en_mask;
> > > +       r = readl(pll->base_addr + REG_CON0) | CON0_BASE_EN;
> > > +       writel(r, pll->base_addr + REG_CON0);
> > > +
> > > +       r = readl(pll->base_addr + REG_CON0) | pll->data->en_mask;
> 
> One more question. I have the feeling that CON0_BASE_EN is what
> enables the clock for good (and pll->data->en_mask is just an
> additional setting/mask, since you could disable the clock by simply
> clearing CON0_BASE_EN). Shouldn't you set pll->data->en_mask _first_,
> then CON0_BASE_EN?
> 

Hi Nicolas,

Actually I had the same question when I first saw it.
But this is the recommended sequence in the PLL application notes.

preapre
{
    | CON0_BASE_EN;
    | pll->data->en_mask;
}

unprepare
{
    ~pll->data->en_mask;
    ~CON0_BASE_EN;
}

> > >         writel(r, pll->base_addr + REG_CON0);
> >
> > As a small optimization, you can do:
> >
> > if (pll->data->en_mask) {
> >    r = readl(pll->base_addr + REG_CON0) | pll->data->en_mask;
> >    writel(r, pll->base_addr + REG_CON0);
> > }
> >
> > >
> > >         __mtk_pll_tuner_enable(pll);
> > > @@ -278,6 +280,10 @@ static void mtk_pll_unprepare(struct clk_hw *hw)
> > >         __mtk_pll_tuner_disable(pll);
> > >
> > >         r = readl(pll->base_addr + REG_CON0);
> > > +       r &= ~pll->data->en_mask;
> >
> > Move this to one line? (so that the code looks symmetrical, too?)
> >
> > > +       writel(r, pll->base_addr + REG_CON0);
> > > +
> > > +       r = readl(pll->base_addr + REG_CON0);
> > >         r &= ~CON0_BASE_EN;
> 
> And ditto, ~CON0_BASE_EN then ~pll->data->en_mask?
> 
> >
> > ditto?
> >
> > >         writel(r, pll->base_addr + REG_CON0);
> > >
> > > --
> > > 1.8.1.1.dirty