linux-kernel - Re: [PATCH v2 3/5] clk: renesas: rzv2h-cpg: Add support for enabling PLLs

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Message-ID: <CAMuHMdXkwUXn0tVVg6BzUbtnSzENGokSY7oXPQW2fuX9QiZz0w@mail.gmail.com>
Date: Fri, 14 Mar 2025 14:04:38 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v2 3/5] clk: renesas: rzv2h-cpg: Add support for enabling PLLs

Hi Prabhakar,

On Mon, 10 Mar 2025 at 19:22, Lad, Prabhakar <prabhakar.csengg@...il.com> wrote:
> On Sun, Mar 9, 2025 at 9:14 PM Prabhakar <prabhakar.csengg@...il.com> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Some RZ/V2H(P) SoC variants do not have a GPU, resulting in PLLGPU being
> > disabled by default in TF-A. Add support for enabling PLL clocks in the
> > RZ/V2H(P) CPG driver to manage this.
> >
> > Introduce `is_enabled` and `enable` callbacks to handle PLL state
> > transitions. With the `enable` callback, PLLGPU will be turned ON only
> > when the GPU node is enabled; otherwise, it will remain off. Define new
> > macros for PLL standby and monitor registers to facilitate this process.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > ---
> > v1->v2
> > - Updated macros to get PLL offsets
> > - Switched to readl_poll_timeout_atomic() and updated the timeout

Thanks for the update!

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

> > --- a/drivers/clk/renesas/rzv2h-cpg.c
> > +++ b/drivers/clk/renesas/rzv2h-cpg.c

> > +static int rzv2h_cpg_pll_clk_enable(struct clk_hw *hw)
> > +{
> > +       struct pll_clk *pll_clk = to_pll(hw);
> > +       struct rzv2h_cpg_priv *priv = pll_clk->priv;
> > +       struct pll pll = pll_clk->pll;
> > +       u32 stby_offset;
> > +       u32 mon_offset;
> > +       u32 val;
> > +       int ret;
> > +
> > +       if (rzv2h_cpg_pll_clk_is_enabled(hw))
> > +               return 0;
> > +
> > +       stby_offset = CPG_PLL_STBY(pll.offset);
> > +       mon_offset = CPG_PLL_MON(pll.offset);
> > +
> > +       writel(CPG_PLL_STBY_RESETB_WEN | CPG_PLL_STBY_RESETB,
> > +              priv->base + stby_offset);
> > +
> > +       /* ensure PLL is in normal mode */
> > +       ret = readl_poll_timeout_atomic(priv->base + mon_offset, val,
> > +                                       (val & (CPG_PLL_MON_RESETB | CPG_PLL_MON_LOCK)) ==
> > +                                       (CPG_PLL_MON_RESETB | CPG_PLL_MON_LOCK), 10, 100);
> This timeout didnt work when I power cycled after a complete shutdown overnight.
>
> I will update the timeout as below, this Ive made sure the below delay
> works OK after complete shutdown.
>
> /*
> * Ensure PLL enters into normal mode
> *
> * Note: There is no HW information about the worst case latency.
> *
> * Since this value might be dependent on external xtal rate, pll
> * rate or even the other emulation clocks rate, use 2000 as a
> * "super" safe value.
> */
> ret = readl_poll_timeout_atomic(priv->base + mon_offset, val,
>                                                     (val &
> (CPG_PLL_MON_RESETB | CPG_PLL_MON_LOCK)) ==
>
> (CPG_PLL_MON_RESETB | CPG_PLL_MON_LOCK), 200, 2000);
>
> Please let me know shall I send v3 with this change or wait for your review.

I can incorporate this fix while queuing in renesas-clk for v6.16.
But, please explain what is "the other emulation clocks rate"?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds