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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Biju Das <biju.das.jz@bp.renesas.com>
Cc: Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	Chris Paterson <Chris.Paterson2@renesas.com>,
	Biju Das <biju.das@bp.renesas.com>,
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>
Subject: Re: [PATCH v2 3/4] drivers: clk: renesas: rzg2l-cpg: Add support to handle coupled clocks
Date: Fri, 13 Aug 2021 14:46:27 +0200	[thread overview]
Message-ID: <CAMuHMdW6xKWp-KKv0exfx-JBb_GXjhvM3hczFSE77j4iORaM3A@mail.gmail.com> (raw)
In-Reply-To: <OS0PR01MB5922495A19B0CDDD50D525D486FA9@OS0PR01MB5922.jpnprd01.prod.outlook.com>

Hi Biju,

On Fri, Aug 13, 2021 at 2:17 PM Biju Das <biju.das.jz@bp.renesas.com> wrote:
> > Subject: Re: [PATCH v2 3/4] drivers: clk: renesas: rzg2l-cpg: Add support
> > to handle coupled clocks
> > On Thu, Aug 12, 2021 at 9:00 AM Biju Das <biju.das.jz@bp.renesas.com>
> > wrote:
> > > > Subject: Re: [PATCH v2 3/4] drivers: clk: renesas: rzg2l-cpg: Add
> > > > support to handle coupled clocks On Tue, Jul 27, 2021 at 4:18 PM
> > > > Biju Das <biju.das.jz@bp.renesas.com>
> > > > wrote:
> > > > > The AXI and CHI clocks use the same register bit for controlling
> > > > > clock output. Add a new clock type for coupled clocks, which sets
> > > > > the CPG_CLKON_ETH.CLK[01]_ON bit when at least one clock is
> > > > > enabled, and clears the bit only when both clocks are disabled.
> > > > >
> > > > > Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > > > Reviewed-by: Lad Prabhakar
> > > > > <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > > >
> > > > Thanks for your patch!
> > > >
> > > > > --- a/drivers/clk/renesas/rzg2l-cpg.c
> > > > > +++ b/drivers/clk/renesas/rzg2l-cpg.c
> > > > > @@ -333,12 +333,16 @@ rzg2l_cpg_register_core_clk(const struct
> > > > cpg_core_clk *core,
> > > > >   * @hw: handle between common and hardware-specific interfaces
> > > > >   * @off: register offset
> > > > >   * @bit: ON/MON bit
> > > > > + * @is_coupled: flag to indicate coupled clock
> > > > > + * @on_cnt: ON count for coupled clocks
> > > > >   * @priv: CPG/MSTP private data
> > > > >   */
> > > > >  struct mstp_clock {
> > > > >         struct clk_hw hw;
> > > > >         u16 off;
> > > > >         u8 bit;
> > > > > +       bool is_coupled;
> > > > > +       u8 on_cnt;
> > > >
> > > > While u8 is probably sufficient, you may want to use unsigned int,
> > > > as there will be a gap anyway due to alignment rules.
> > > >
> > > > >         struct rzg2l_cpg_priv *priv;  };
> > > > >
> > > > > @@ -392,11 +396,37 @@ static int rzg2l_mod_clock_endisable(struct
> > > > > clk_hw *hw, bool enable)
> > > > >
> > > > >  static int rzg2l_mod_clock_enable(struct clk_hw *hw)  {
> > > > > +       struct mstp_clock *clock = to_mod_clock(hw);
> > > > > +       struct rzg2l_cpg_priv *priv = clock->priv;
> > > > > +       unsigned long flags;
> > > > > +
> > > > > +       spin_lock_irqsave(&priv->rmw_lock, flags);
> > > > > +       clock->on_cnt++;
> > > > > +       if (clock->is_coupled && clock->on_cnt > 1) {
> > > > > +               spin_unlock_irqrestore(&priv->rmw_lock, flags);
> > > > > +               return 1;
> > > > > +       }
> > > > > +
> > > > > +       spin_unlock_irqrestore(&priv->rmw_lock, flags);
> > > >
> > > > I think you can avoid taking the spinlock and touching the counter
> > > > if the is_coupled flag is not set.
> > >
> > > OK.
> > >
> > > >
> > > > > +
> > > > >         return rzg2l_mod_clock_endisable(hw, true);  }
> > > >
> > > > However, I'm wondering how this can work?
> > > >
> > > >       DEF_COUPLED("eth0_axi", R9A07G044_ETH0_CLK_AXI,
> > R9A07G044_CLK_M0,
> > > >                               0x57c, 0),
> > > >       DEF_COUPLED("eth0_chi", R9A07G044_ETH0_CLK_CHI,
> > R9A07G044_CLK_ZT,
> > > >                               0x57c, 0),
> > > >
> > > > This will create 2 independent clocks, each with their own
> > > > mstp_clock structure that has the is_coupled flag set.  Hence each
> > > > clock has its own counter. Shouldn't the counter be shared?
> > > > Am I missing something?
> > >
> > > Oops. You are correct. I need to add this counter to priv instead of
> > mstp_clocks.
> >
> > On second thought, a counter is overkill. A simple flag should be
> > sufficient, as the clk core only calls .{en,dis}able() when the clock is
> > {dis,en}enabled.
>
> Just to clarify, simple flag, did you mean to use bit flag? (ie, 2 bits , since we have 2 module clocks)
> when core clock calls enable, set a bit and reset the bit during disable.
>
> Then based on the 2bits, either turn on/off clock or just return the status.
>
> Please correct me, if my understanding wrong?

Just one bool or bit in a bitfield, the second flag will be in the
other struct mstp_clock (can there be three coupled clocks?).

So I think something like below should work:

     struct mstp_clock {
            struct clk_hw hw;
            u16 off;
            u8 bit;
    +       bool enabled;
            struct rzg2l_cpg_priv *priv;
    +       struct mstp_clock *siblings;
     };

.enabled needs to track the soft state of the clock.
The actual coupling is handled through .siblings, which points to the
other coupled clock (or forms a circular list if you can have more than
two coupled clocks).  When registering a clock, if mod->is_coupled
is set, you walk all already registered module clocks to find one
with the same off and bit, and link them together.

In .{en,dis}able(), you only {en,dis}able the hardware clock if all
other clocks in the list are disabled.

if it turns out too costly to add a pointer to each clock (depends
on slab granularity), you can also use a different struct for coupled
clocks:

    struct mstp_coupled_clock {
            struct mstp_clock mstp;
            struct mstp_coupled_clock *siblings;
    };

but then you do need another flag in mstp_clock to indicate it is
a coupled clock, that can be converted to mstp_coupled_clock using
container_of().

Does that make sense?
Have a nice weekend!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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

  reply	other threads:[~2021-08-13 12:46 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 14:17 [PATCH v2 0/4] Add GbEthernet Clock support Biju Das
2021-07-27 14:17 ` [PATCH v2 1/4] drivers: clk: renesas: rzg2l-cpg: Add support to handle MUX clocks Biju Das
2021-07-27 14:17 ` [PATCH v2 2/4] drivers: clk: renesas: r9a07g044-cpg: Add ethernet clock sources Biju Das
2021-07-27 14:17 ` [PATCH v2 3/4] drivers: clk: renesas: rzg2l-cpg: Add support to handle coupled clocks Biju Das
2021-08-11 10:18   ` Geert Uytterhoeven
2021-08-12  6:59     ` Biju Das
2021-08-12  7:54       ` Geert Uytterhoeven
2021-08-13 12:16         ` Biju Das
2021-08-13 12:46           ` Geert Uytterhoeven [this message]
2021-08-13 18:01             ` Biju Das
2021-07-27 14:17 ` [PATCH v2 4/4] drivers: clk: renesas: r9a07g044-cpg: Add GbEthernet clock/reset Biju Das

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