linux-kernel - Re: [PATCH 2/3] clk: meson: clk-pll: remove od parameters

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Date:   Sat, 21 Jul 2018 23:37:54 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     jbrunet@...libre.com
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, khilman@...libre.com
Subject: Re: [PATCH 2/3] clk: meson: clk-pll: remove od parameters

Hi Jerome,

On Sat, Jul 21, 2018 at 10:42 PM Jerome Brunet <jbrunet@...libre.com> wrote:
>
> On Sat, 2018-07-21 at 22:01 +0200, Martin Blumenstingl wrote:
> > > +static struct clk_regmap gxbb_hdmi_pll_od = {
> > > +       .data = &(struct clk_regmap_div_data){
> > > +               .offset = HHI_HDMI_PLL_CNTL2,
> > > +               .shift = 16,
> > > +               .width = 2,
> > > +               .flags = CLK_DIVIDER_POWER_OF_TWO,
> > > +       },
> > > +       .hw.init = &(struct clk_init_data){
> > > +               .name = "hdmi_pll_od",
> > > +               .ops = &clk_regmap_divider_ro_ops,
> > > +               .parent_names = (const char *[]){ "hdmi_pll_dco" },
> > > +               .num_parents = 1,
> > > +               .flags = CLK_GET_RATE_NOCACHE,
> >
> > why do we need CLK_GET_RATE_NOCACHE here?
> > also, shouldn't all _od clocks use CLK_SET_RATE_PARENT?
> > (this applies to all new _od clocks, not just this one)
>
> The goal was to retain the original behavior of the clock.
> The pll has CLK_GET_RATE_NOCACHE, which is why I put it again in the od
> dividers. Same goes for ro_ops
I missed that - thanks for the explanation!

> For the particular case of the HDMI PLL, the display driver still set the pll
> parameters m, n and ods directly which justify CLK_GET_RATE_NOCACHE for now.
> Of course, the goal is to remove this flag someday. I think there has been some
> good progress in the DRM driver to reach this goal.
>
> If we think the use CLK_GET_RATE_NOCACHE is not justified for some other plls, I
> would prefer if it was addressed in another patchset.
now that the reason is clear to me: I fully agree!

> Regarding SET_RATE_PARENT, with the pll set with ro_ops, it does not change
> anything but, I agree, it would be better to set flag for the future.
I see
adding SET_RATE_PARENT will probably save a bit of headache later on
when enabling the write operation of the PLL and then wondering why
the frequency is not changed


Regards
Martin