Message-ID: <cc74422d-962f-4da5-867b-158a71db1a7b@collabora.com>
Date: Thu, 29 Feb 2024 10:45:27 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Pin-yen Lin <treapking@...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 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.

Can you please do a test for that, or should I?

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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