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

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Message-ID: <CANMq1KAYg2+RQiF0w7-2FKZj1QwoPDsXtmak-DHfserRjX-TWA@mail.gmail.com>
Date:   Wed, 29 Jul 2020 19:02:52 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Weiyi Lu <weiyi.lu@...iatek.com>
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, 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?

> >         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