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Date: Thu, 7 Mar 2024 12:22:36 +0100
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Subject: Re: [PATCH v3 1/2] clk: mediatek: Introduce need_pm_runtime to
 mtk_clk_desc
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To: Pin-yen Lin <treapking@chromium.org>, Chen-Yu Tsai <wenst@chromium.org>
Cc: Michael Turquette <mturquette@baylibre.com>,
 Stephen Boyd <sboyd@kernel.org>, Matthias Brugger <matthias.bgg@gmail.com>,
 Weiyi Lu <weiyi.lu@mediatek.com>, linux-kernel@vger.kernel.org,
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From: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
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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

> 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
>>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>>>
>>