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Message-ID: <CAMuHMdXFtBmjDu=1RS2MLNYzhZ0fmpT7+1QbA9p4LvoLHitOuw@mail.gmail.com>
Date: Fri, 9 May 2025 14:34:46 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: mturquette@...libre.com, sboyd@...nel.org, robh@...nel.org,
krzk+dt@...nel.org, conor+dt@...nel.org, magnus.damm@...il.com,
linux-renesas-soc@...r.kernel.org, linux-clk@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH 3/7] clk: renesas: rzg2l-cpg: Add support for MSTOP in
clock enable/disable API
Hi Claudiu,
On Fri, 9 May 2025 at 12:54, Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> On 07.05.2025 18:42, Geert Uytterhoeven wrote:
> > On Thu, 10 Apr 2025 at 16:06, Claudiu <claudiu.beznea@...on.dev> wrote:
> >> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> >>
> >> The RZ/{G2L, V2L, G3S} CPG versions support a feature called MSTOP. Each
> >> module has one or more MSTOP bits associated with it, and these bits need
> >> to be configured along with the module clocks. Setting the MSTOP bits
> >> switches the module between normal and standby states.
> >>
> >> Previously, MSTOP support was abstracted through power domains
> >> (struct generic_pm_domain::{power_on, power_off} APIs). With this
> >> abstraction, the order of setting the MSTOP and CLKON bits was as follows:
> >>
> >> Previous Order:
> >> A/ Switching to Normal State (e.g., during probe):
> >> 1/ Clear module MSTOP bits
> >> 2/ Set module CLKON bits
> >>
> >> B/ Switching to Standby State (e.g., during remove):
> >> 1/ Clear CLKON bits
> >> 2/ Set MSTOP bits
> >>
> >> However, in some cases (when the clock is disabled through devres), the
> >> order may have been (due to the issue described in link section):
> >>
> >> 1/ Set MSTOP bits
> >> 2/ Clear CLKON bits
> >>
> >> Recently, the hardware team has suggested that the correct order to set
> >> the MSTOP and CLKON bits is:
> >>
> >> Updated Order:
> >> A/ Switching to Normal State (e.g., during probe):
> >> 1/ Set CLKON bits
> >> 2/ Clear MSTOP bits
> >>
> >> B/ Switching to Standby State (e.g., during remove):
> >> 1/ Set MSTOP bits
> >> 2/ Clear CLKON bits
> >>
> >> To prevent future issues due to incorrect ordering, the MSTOP setup has
> >> now been implemented in rzg2l_mod_clock_endisable(), ensuring compliance
> >> with the sequence suggested in Figure 41.5: Module Standby Mode Procedure
> >> from the RZ/G3S HW manual.
> >>
> >> Additionally, since multiple clocks of a single module may be mapped to a
> >> single MSTOP bit, MSTOP setup is reference-counted.
> >>
> >> Furthermore, as all modules start in the normal state after reset, if the
> >> module clocks are disabled, the module state is switched to standby. This
> >> prevents keeping the module in an invalid state, as recommended by the
> >> hardware team.
> >>
> >> Link: https://lore.kernel.org/all/20250215130849.227812-1-claudiu.beznea.uj@bp.renesas.com/
> >> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> >
> > Thanks for your patch!
> >
> >> --- a/drivers/clk/renesas/rzg2l-cpg.c
> >> +++ b/drivers/clk/renesas/rzg2l-cpg.c
> >> +/* Need to be called with a lock held to avoid concurrent access to mstop->refcnt. */
> >> +static void rzg2l_mod_clock_module_set_state(struct mstp_clock *clock,
> >> + bool standby)
> >> +{
> >> + struct rzg2l_cpg_priv *priv = clock->priv;
> >> + struct mstop *mstop = clock->mstop;
> >> + bool update = false;
> >> + u32 value;
> >> +
> >> + if (!mstop)
> >> + return;
> >> +
> >> + value = MSTOP_MASK(mstop->conf) << 16;
> >> +
> >> + if (standby) {
> >> + unsigned int criticals = 0;
> >> +
> >> + for (u8 i = 0; i < clock->num_shared_mstop_clks; i++) {
> >
> > unsigned int
> >
> >> + struct mstp_clock *clk = clock->shared_mstop_clks[i];
> >> +
> >> + if (clk->critical)
> >> + criticals++;
> >> + }
> >> +
> >> + /* Increment if clock is critical, too. */
> >> + if (clock->critical)
> >> + criticals++;
> >
> > If clock->shared_mstop_clks[] would include the current clock, then
> > (a) this test would not be needed, and
>
> Agree!
>
> > (b) all clocks sharing the same mstop could share a single
> > clock->shared_mstop_clks[] array.
>
> I'll look into this but I'm not sure how should I do it w/o extra
> processing at the end of registering all the clocks. FWICT, that would
> involve freeing some shared_mstop_clks arrays and using a single reference
> as the shared_mstop_clks[] is updated after every clock is registered. Can
> you please let me know if this what you are thinking about?
Currently, when detecting two clocks share the same mstop,
you (re)allocate each clock's shared_mstop_clks[], and add the
other clock:
rzg2l_cpg_add_shared_mstop_clock(priv->dev, clock, clk);
rzg2l_cpg_add_shared_mstop_clock(priv->dev, clk, clock);
Instead, call rzg2l_cpg_add_shared_mstop_clock() once, and modify
rzg2l_cpg_add_shared_mstop_clock() to not only realloc the target's
shared_mstop_clks[], but also loop over all its existing entries,
and update their shared_mstop_clks[] pointers.
> >> + for (unsigned int i = 0; i < priv->num_mod_clks; i++) {
> >> + struct mstp_clock *clk;
> >> + struct clk_hw *hw;
> >> + u32 val;
> >> +
> >> + if (priv->clks[priv->num_core_clks + i] == ERR_PTR(-ENOENT))
> >> + continue;
> >> +
> >> + hw = __clk_get_hw(priv->clks[priv->num_core_clks + i]);
> >> + clk = to_mod_clock(hw);
> >
> > As this patch adds four more loops iterating over all module clocks
> > and skipping empty entries, I think it is worthwhile to introduce a
> > custom for_each_mstp_clock()-iterator.
>
> I was thinking about it and I tried do it with a macro, keeping this code
> in it:
>
> for (unsigned int i = 0; i < priv->num_mod_clks; i++) {
> struct mstp_clock *clk;
> struct clk_hw *hw;
> u32 val;
>
> if (priv->clks[priv->num_core_clks + i] == ERR_PTR(-ENOENT))
> continue;
>
> but it was a complicated macro and abandoned it in the end.
Yes, the implementation would be complicated, but the semantics
would be clear. The kernel already has complex macros like
for_each_nest_rmap_safe() and for_each_oldnew_connector_in_state().
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
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