RE: [PATCH v2 3/4] drivers: clk: renesas: rzg2l-cpg: Add support to handle coupled clocks

[Biju Das <biju.das.jz@bp.renesas.com>]

Hi Geert,

Thanks for the feedback.

> Subject: Re: [PATCH v2 3/4] drivers: clk: renesas: rzg2l-cpg: Add support
> to handle coupled clocks
> 
> Hi Biju,
> 
> 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?

Cheers,
Biju