Re: [PATCH 3/7] clk: renesas: rzg2l-cpg: Add support for MSTOP in clock enable/disable API

[Claudiu Beznea <claudiu.beznea@tuxon.dev>]

Hi, Geert,

On 09.05.2025 15:34, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> On Fri, 9 May 2025 at 12:54, Claudiu Beznea <claudiu.beznea@tuxon.dev> wrote:
>> On 07.05.2025 18:42, Geert Uytterhoeven wrote:
>>> On Thu, 10 Apr 2025 at 16:06, Claudiu <claudiu.beznea@tuxon.dev> wrote:
>>>> From: Claudiu Beznea <claudiu.beznea.uj@bp.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@bp.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.
I tried this approach but w/o complicated further the code I can't keep
track of whether the "to be updated" (not reallocated) shared_mstop_clks[]
pointers were previously updated pointers or devm_krealloc()'ed ones. I
need this to properly free the unused arrays. Calling devm_kfree() on a
non-devres resource triggers a WARN_ON() for each call.

Because of this I prepared a new version where the duplicated lists are
freed after all the mod clocks were initialized. I'll publish it soon.

Thank you,
Claudiu