Re: [PATCH v3 1/2] clk: mediatek: Introduce need_pm_runtime to mtk_clk_desc

Pin-yen Lin
2024-03-07T11:11:09Z

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?

Regards,
Pin-yen

On Thu, Feb 29, 2024 at 6:36 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora.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@collabora.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@collabora.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@chromium.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@chromium.org>
> >>>>>
> >>>>> Reviewed-by: Chen-Yu Tsai <wenst@chromium.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
> >>>>>>
> >>>>
> >>>>
> >>>>
> >>
> >>
> >>
>