Message-ID: <ae89f215-c97d-496e-9640-c87ccac1c991@collabora.com>
Date: Tue, 12 Mar 2024 10:45:16 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Pin-yen Lin <treapking@...omium.org>
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

Il 12/03/24 10:35, Pin-yen Lin ha scritto:
> 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.
> 

You're welcome. Looking forward to see the new patch!

Cheers,
Angelo

> 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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