linux-kernel - Re: [PATCH] arm64: dts: mediatek: mt8183: Add power-domains properity to mfgcfg

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Message-ID: <CAGXv+5GpTJzMHxY+J6PshW6-xLfc5G3DTuAG4d9eCc+=WWRd9A@mail.gmail.com>
Date: Thu, 29 Feb 2024 15:13:34 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Matthias Brugger <matthias.bgg@...il.com>, Ikjoon Jang <ikjn@...omium.org>, 
	devicetree@...r.kernel.org, linux-mediatek@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Weiyi Lu <weiyi.lu@...iatek.com>
Subject: Re: [PATCH] arm64: dts: mediatek: mt8183: Add power-domains properity
 to mfgcfg

On Mon, Feb 26, 2024 at 4:54 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Il 23/02/24 10:11, Chen-Yu Tsai ha scritto:
> > From: Ikjoon Jang <ikjn@...omium.org>
> >
> > mfgcfg clock is under MFG_ASYNC power domain.
> >
> > Fixes: e526c9bc11f8 ("arm64: dts: Add Mediatek SoC MT8183 and evaluation board dts and Makefile")
> > Fixes: 37fb78b9aeb7 ("arm64: dts: mediatek: Add mt8183 power domains controller")
> > Signed-off-by: Weiyi Lu <weiyi.lu@...iatek.com>
> > Signed-off-by: Ikjoon Jang <ikjn@...omium.org>
> > Reviewed-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> > Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> > ---
> > This patch is long overdue. Could we merge it for fixes for this or the
> > next release?
> >
>
> A clock controller that needs a power domain? Can you please describe the issue
> that you're trying to solve with this?

Our issue tracker doesn't have much on this. But this was part of the initial
submission for MT8183, but somehow got left out. The clk driver patch to
enable runtime PM was even merged, but was effectively reverted following
the clk driver rework.

> It's not very uncommon but I'm not entirely convinced that this is right, because
> the MFG_BG3D is a gate - and it's *not* outputting a clock rate on its own: the
> mfgcfg is entirely GPU related and if there is no GPU support this clock is not
> even ever needed.

It could be just a gate, or could be a buffer. Either way, the registers to
control said device could be in a power domain that is not always on. I don't
think this can be ruled out.

And if the registers are in a powered down domain, then either the readout
would be bogus (if access isolation is implemented) or just hang the system.

ChenYu

> MediaTek, can you please clarify if (and why) this gate clock needs a MTCMOS to
> be ungated?
>
> Thanks,
> Angelo
>
> > Changes since v2:
> > - Rebased onto current tree
> > - Added Fixes tags
> > - Fix up subject prefix
> >
> >   arch/arm64/boot/dts/mediatek/mt8183.dtsi | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/boot/dts/mediatek/mt8183.dtsi b/arch/arm64/boot/dts/mediatek/mt8183.dtsi
> > index 93dfbf130231..774ae5d9143f 100644
> > --- a/arch/arm64/boot/dts/mediatek/mt8183.dtsi
> > +++ b/arch/arm64/boot/dts/mediatek/mt8183.dtsi
> > @@ -1637,6 +1637,7 @@ mfgcfg: syscon@...00000 {
> >                       compatible = "mediatek,mt8183-mfgcfg", "syscon";
> >                       reg = <0 0x13000000 0 0x1000>;
> >                       #clock-cells = <1>;
> > +                     power-domains = <&spm MT8183_POWER_DOMAIN_MFG_ASYNC>;
> >               };
> >
> >               gpu: gpu@...40000 {
>
>