Message-ID: <CAEXTbpeSyh1YfKsM8cqRjOFA7Ww4ooRxgCxMwXw2F4uCyX=OBg@mail.gmail.com>
Date: Tue, 12 Mar 2024 17:35:23 +0800
From: Pin-yen Lin <treapking@...omium.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Chen-Yu Tsai <wenst@...omium.org>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>, 
	Weiyi Lu <weiyi.lu@...iatek.com>, linux-kernel@...r.kernel.org, 
	linux-clk@...r.kernel.org, linux-mediatek@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/2] clk: mediatek: Introduce need_pm_runtime to mtk_clk_desc

Hi Angelo

On Thu, Mar 7, 2024 at 7:22 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Il 07/03/24 12:10, Pin-yen Lin ha scritto:
> > Hi Angelo and Chen-yu,
> >
> > I tried enabling the runtime PM regardless of the .need_pm_runtime
> > flag, and my MT8183 device works well with that with no obvious boot
> > regression.
> >
> > Should I send out another patch that always enables runtime PM in
> > __mtk_clk_simple_probe()? Or is there anything I should test?
> >
>
> Hello Pin-yen,
>
> as I discussed with Chen-Yu - yes, we must make sure that this does not
> create any regression on machines running on other SoC models.
>
> I think it's unlikely that it does, but since the HW is available, being
> extremely careful with validating this change is a good idea :-)
>
> If you can/want to test before we do, sure, please send the new patch and,
> when you do, please say that you tested it and on which SoCs; as long as
> it's not just one SoC, that'll be good enough for me.
>
> P.S.: Please don't top-post!
>
> Cheers,
> Angelo

I just tried this on MT8192 and the system looks healthy as well. I'll
send out a patch to enable the runtime PM for all mediatek clock
controllers.

Thanks for your time on reviewing this, and sorry for the top-posting.

Regards,
Pin-yen

>
> > Regards,
> > Pin-yen
> >
> > On Thu, Feb 29, 2024 at 6:36 PM AngeloGioacchino Del Regno
> > <angelogioacchino.delregno@...labora.com> wrote:
> >>
> >> Il 29/02/24 11:34, Chen-Yu Tsai ha scritto:
> >>> On Thu, Feb 29, 2024 at 5:45 PM AngeloGioacchino Del Regno
> >>> <angelogioacchino.delregno@...labora.com> wrote:
> >>>>
> >>>> Il 29/02/24 08:17, Chen-Yu Tsai ha scritto:
> >>>>> On Mon, Feb 26, 2024 at 7:16 PM AngeloGioacchino Del Regno
> >>>>> <angelogioacchino.delregno@...labora.com> wrote:
> >>>>>>
> >>>>>> Il 23/02/24 05:27, Chen-Yu Tsai ha scritto:
> >>>>>>> On Mon, Jan 8, 2024 at 4:18 PM Pin-yen Lin <treapking@...omium.org> wrote:
> >>>>>>>>
> >>>>>>>> Introduce a new need_pm_runtime variable to mtk_clk_desc to indicate
> >>>>>>>> this clock controller needs runtime PM for its operations.
> >>>>>>>> Also do a runtime PM get on the clock controller during the
> >>>>>>>> probing stage to workaround a possible deadlock.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Pin-yen Lin <treapking@...omium.org>
> >>>>>>>
> >>>>>>> Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>
> >>>>>>>
> >>>>>>> The patch itself looks fine.
> >>>>>>>
> >>>>>>> Besides the MT8183 MFG clock issues, we do actually need this for the
> >>>>>>> MT8192 ADSP clock. Its power domain is not enabled by default.
> >>>>>>>
> >>>>>>
> >>>>>> ...but on MT8195 the ADSP clock works - because the ADSP node exists.
> >>>>>
> >>>>> That's an indirect dependency that should not be relied on. Say the clock
> >>>>> driver probed but the ADSP hasn't, and you try to read out the current
> >>>>> status. What would happen?
> >>>>>
> >>>>> - Read out works fine, because the power domain is default on, and hasn't
> >>>>>      been turned off by late cleanup
> >>>>> - Read out is bogus (but you can't tell)
> >>>>> - Read out hangs.
> >>>>>
> >>>>> The third is what happens on MT8192. There's still some issues on that
> >>>>> front, as even after I applied the ADSP power domain patches from MediaTek,
> >>>>> the readout was still hanging.
> >>>>>
> >>>>
> >>>> That MT8192 lockup story is getting crazy in my head... anyway, besides that,
> >>>> I get the point - I was somehow ignoring the fact that kernel modules do exist.
> >>>>
> >>>> Eh, sorry about that :-)
> >>>>
> >>>>>> This poses a question: should we make clock controllers depend on power domains,
> >>>>>> or should we keep everything powered off (hence clocks down - no power consumption)
> >>>>>> *unless* the user exists?
> >>>>>
> >>>>> That's a policy discussion separate from actual hardware dependencies.
> >>>>> *If* the clock controller needs the power domain to be active for the
> >>>>> registers to be accessed, the clock controller *must* have a direct
> >>>>> dependency on the power domain.
> >>>>>
> >>>>
> >>>> I admit I should've worded that better.
> >>>>
> >>>> "should we make clock controllers depend on power domains" was actually implying
> >>>> "IF those need one" :-)
> >>>>
> >>>> I really wonder if - at this point - it's simply a better idea to not restrict
> >>>> the call to devm_pm_runtime_enable/resume_and_get to `need_runtime_pm == true`.
> >>>>
> >>>> Do we really need to exclude that on other clock controllers that don't have
> >>>> any power domain dependency? Any side effect?
> >>>>
> >>>> Saying this because if we can avoid yet another per-SoC flag I'm really happy,
> >>>> as readability is also impacted and besides - if we ever find out that one of
> >>>> those need a power domain in the future, we'll need just one commit and just
> >>>> only in the devicetree, instead of enabling a flag in driver X as well as that,
> >>>> avoiding some (potentially unnecessary) noise... I guess.
> >>>>
> >>>> P.S.: I just noticed that the return value for the devm_pm_runtime_enable() call
> >>>>          is not being checked!
> >>>>
> >>>> .......
> >>>>
> >>>> In short....
> >>>>
> >>>> Chen-Yu, at this point, do you have any reason why we wouldn't be able and/or it
> >>>> wouldn't be a good idea to just avoid adding the `need_runtime_pm` flag (meaning
> >>>> that we perform pm_runtime calls for all clock drivers unconditionally)?
> >>>>
> >>>> If this is about longer boot time, I don't think that it's going to be more than
> >>>> a millisecond or two, so that should be completely ignorable.
> >>>
> >>> I think it's just more of a "don't enable features you don't need" thing.
> >>> We already ran into a weird deadlock, which is why the devm_pm_runtime_enable()
> >>> call has that comment.
> >>>
> >>> I don't think anyone has actually looked at it. As you said it shouldn't be
> >>> much, at least during boot time. It's one call per clock controller.
> >>>
> >>>> Can you please do a test for that, or should I?
> >>>
> >>> The earliest I can work on it would be some time next week. Does that work
> >>> for you?
> >>>
> >>
> >> The earliest I'd be able to work on this myself would be at the end of next
> >> week if not later.. so yes, please take your time, no worries.
> >>
> >> Thank you!
> >>
> >>> ChenYu
> >>>
> >>>> Cheers
> >>>> Angelo
> >>>>
> >>>>>> For the second one, this means that the *device* gets the power domain (adsp), and
> >>>>>> not the clock controller (which clocks are effectively useless if there's no user).
> >>>>>
> >>>>> No. See my previous paragraph.
> >>>>>
> >>>>> ChenYu
> >>>>>
> >>>>>> Angelo
> >>>>>>
> >>>>>>>> ---
> >>>>>>>>
> >>>>>>>> Changes in v3:
> >>>>>>>> - Update the commit message and the comments before runtime PM call
> >>>>>>>>
> >>>>>>>> Changes in v2:
> >>>>>>>> - Fix the order of error handling
> >>>>>>>> - Update the commit message and add a comment before the runtime PM call
> >>>>>>>>
> >>>>>>>>      drivers/clk/mediatek/clk-mtk.c | 19 +++++++++++++++++++
> >>>>>>>>      drivers/clk/mediatek/clk-mtk.h |  2 ++
> >>>>>>>>      2 files changed, 21 insertions(+)
> >>>>>>>>
> >>>>>>>> diff --git a/drivers/clk/mediatek/clk-mtk.c b/drivers/clk/mediatek/clk-mtk.c
> >>>>>>>> index 2e55368dc4d8..ba1d1c495bc2 100644
> >>>>>>>> --- a/drivers/clk/mediatek/clk-mtk.c
> >>>>>>>> +++ b/drivers/clk/mediatek/clk-mtk.c
> >>>>>>>> @@ -13,6 +13,7 @@
> >>>>>>>>      #include <linux/of.h>
> >>>>>>>>      #include <linux/of_address.h>
> >>>>>>>>      #include <linux/platform_device.h>
> >>>>>>>> +#include <linux/pm_runtime.h>
> >>>>>>>>      #include <linux/slab.h>
> >>>>>>>>
> >>>>>>>>      #include "clk-mtk.h"
> >>>>>>>> @@ -494,6 +495,18 @@ static int __mtk_clk_simple_probe(struct platform_device *pdev,
> >>>>>>>>                             return IS_ERR(base) ? PTR_ERR(base) : -ENOMEM;
> >>>>>>>>             }
> >>>>>>>>
> >>>>>>>> +
> >>>>>>>> +       if (mcd->need_runtime_pm) {
> >>>>>>>> +               devm_pm_runtime_enable(&pdev->dev);
> >>>>>>>> +               /*
> >>>>>>>> +                * Do a pm_runtime_resume_and_get() to workaround a possible
> >>>>>>>> +                * deadlock between clk_register() and the genpd framework.
> >>>>>>>> +                */
> >>>>>>>> +               r = pm_runtime_resume_and_get(&pdev->dev);
> >>>>>>>> +               if (r)
> >>>>>>>> +                       return r;
> >>>>>>>> +       }
> >>>>>>>> +
> >>>>>>>>             /* Calculate how many clk_hw_onecell_data entries to allocate */
> >>>>>>>>             num_clks = mcd->num_clks + mcd->num_composite_clks;
> >>>>>>>>             num_clks += mcd->num_fixed_clks + mcd->num_factor_clks;
> >>>>>>>> @@ -574,6 +587,9 @@ static int __mtk_clk_simple_probe(struct platform_device *pdev,
> >>>>>>>>                             goto unregister_clks;
> >>>>>>>>             }
> >>>>>>>>
> >>>>>>>> +       if (mcd->need_runtime_pm)
> >>>>>>>> +               pm_runtime_put(&pdev->dev);
> >>>>>>>> +
> >>>>>>>>             return r;
> >>>>>>>>
> >>>>>>>>      unregister_clks:
> >>>>>>>> @@ -604,6 +620,9 @@ static int __mtk_clk_simple_probe(struct platform_device *pdev,
> >>>>>>>>      free_base:
> >>>>>>>>             if (mcd->shared_io && base)
> >>>>>>>>                     iounmap(base);
> >>>>>>>> +
> >>>>>>>> +       if (mcd->need_runtime_pm)
> >>>>>>>> +               pm_runtime_put(&pdev->dev);
> >>>>>>>>             return r;
> >>>>>>>>      }
> >>>>>>>>
> >>>>>>>> diff --git a/drivers/clk/mediatek/clk-mtk.h b/drivers/clk/mediatek/clk-mtk.h
> >>>>>>>> index 22096501a60a..c17fe1c2d732 100644
> >>>>>>>> --- a/drivers/clk/mediatek/clk-mtk.h
> >>>>>>>> +++ b/drivers/clk/mediatek/clk-mtk.h
> >>>>>>>> @@ -237,6 +237,8 @@ struct mtk_clk_desc {
> >>>>>>>>
> >>>>>>>>             int (*clk_notifier_func)(struct device *dev, struct clk *clk);
> >>>>>>>>             unsigned int mfg_clk_idx;
> >>>>>>>> +
> >>>>>>>> +       bool need_runtime_pm;
> >>>>>>>>      };
> >>>>>>>>
> >>>>>>>>      int mtk_clk_pdev_probe(struct platform_device *pdev);
> >>>>>>>> --
> >>>>>>>> 2.43.0.472.g3155946c3a-goog
> >>>>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>
> >>>>
> >>>>
> >>
>
>
>

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