linux-kernel - Re: [PATCH 5/6] arm64: dts: mediatek: mt8173: Fix MFG

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Date: Wed, 5 Jun 2024 13:25:31 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Chen-Yu Tsai <wenst@...omium.org>
Cc: Frank Binns <frank.binns@...tec.com>, Matt Coster
 <matt.coster@...tec.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 dri-devel@...ts.freedesktop.org, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] arm64: dts: mediatek: mt8173: Fix MFG_ASYNC power
 domain clock

Il 05/06/24 10:25, Chen-Yu Tsai ha scritto:
> On Thu, May 30, 2024 at 6:03 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com> wrote:
>>
>> Il 30/05/24 10:35, Chen-Yu Tsai ha scritto:
>>> The MFG_ASYNC domain, which is likely associated to the whole MFG block,
>>> currently specifies clk26m as its domain clock. This is bogus, since the
>>> clock is an external crystal with no controls. Also, the MFG block has
>>> a independent CLK_TOP_AXI_MFG_IN_SEL clock, which according to the block
>>> diagram, gates access to the hardware registers. Having this one as the
>>> domain clock makes much more sense. This also fixes access to the MFGTOP
>>> registers.
>>>
>>> Change the MFG_ASYNC domain clock to CLK_TOP_AXI_MFG_IN_SEL.
>>>
>>> Fixes: 8b6562644df9 ("arm64: dts: mediatek: Add mt8173 power domain controller")
>>> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
>>
>> Just one question... what happens if there's no GPU support at all and this
>> power domain gets powered off?
>>
>> I expect the answer to be "nothing", so I'm preventively giving you my
> 
> Well it's powered off by default. Just double checked, and without the final
> patch:
> 
> # cat /sys/kernel/debug/pm_genpd/pm_genpd_summary
> domain                          status          children
>              performance
>      /device                                             runtime status
> ----------------------------------------------------------------------------------------------
> mfg                             off-0
>              0
> mfg_2d                          off-0
>              0
>                                                  mfg
> mfg_async                       off-0
>              0
>                                                  mfg_2d
> 
> And with the last patch but with the powervr removed:
> 
> # cat /sys/kernel/debug/pm_genpd/pm_genpd_summary
> domain                          status          children
>              performance
>      /device                                             runtime status
> ----------------------------------------------------------------------------------------------
> mfg_apm                         off-0
>              0
> mfg                             off-0
>              0
>                                                  mfg_apm
>      /devices/platform/soc/13fff000.clock-controller     suspended
>              0
> mfg_2d                          off-0
>              0
>                                                  mfg
> mfg_async                       off-0
>              0
>                                                  mfg_2d
> 
> Things seem to work OK. I can SSH in, and the framebuffer console on the screen
> works fine.
> 
> 
> Note that accessing the regmap through debugfs doesn't do much good. regmap
> doesn't handle runtime PM. And the syscon regmap isn't even tied to a
> struct device. Dumping the regmap through debugfs while the power domain
> is off gives all zeroes, likely due to bus isolation.
> 

The last part where you say "gives all zeroes" is actually the best outcome that
I could have ever expected.

So, well, many thanks for this very nice analysis and test.

>> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

I confirm my green light. It's beautiful when this kind of patches come upstream
especially with your replies actually removing any kind of possible doubt.

> 
> Thanks!

Thank *you* for caring about this old platform!

Cheers,
Angelo

> 
> ChenYu
> 
>> ....but if I'm wrong and the answer isn't exactly "nothing", then I still agree
>> with this commit, but only after removing the Fixes tag.
>>
>> Cheers,
>> Angelo
>>
>>> ---
>>>    arch/arm64/boot/dts/mediatek/mt8173.dtsi | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8173.dtsi b/arch/arm64/boot/dts/mediatek/mt8173.dtsi
>>> index 3458be7f7f61..136b28f80cc2 100644
>>> --- a/arch/arm64/boot/dts/mediatek/mt8173.dtsi
>>> +++ b/arch/arm64/boot/dts/mediatek/mt8173.dtsi
>>> @@ -497,7 +497,7 @@ power-domain@...173_POWER_DOMAIN_USB {
>>>                                };
>>>                                mfg_async: power-domain@...173_POWER_DOMAIN_MFG_ASYNC {
>>>                                        reg = <MT8173_POWER_DOMAIN_MFG_ASYNC>;
>>> -                                     clocks = <&clk26m>;
>>> +                                     clocks = <&topckgen CLK_TOP_AXI_MFG_IN_SEL>;
>>>                                        clock-names = "mfg";
>>>                                        #address-cells = <1>;
>>>                                        #size-cells = <0>;
>>
>>