linux-kernel - Re: [PATCH] arm64: dts: mediatek: mt8192-asurada: Update min voltage constraint for Vgpu

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Date: Thu, 14 Mar 2024 11:02:58 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Pin-yen Lin <treapking@...gle.com>
Cc: Pin-yen Lin <treapking@...omium.org>,
 Matthias Brugger <matthias.bgg@...il.com>, Chen-Yu Tsai
 <wenst@...omium.org>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org,
 Nícolas F . R . A . Prado <nfraprado@...labora.com>,
 devicetree@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: mediatek: mt8192-asurada: Update min voltage
 constraint for Vgpu

Il 14/03/24 10:59, Pin-yen Lin ha scritto:
> Hi Angelo,
> 
> On Wed, Mar 13, 2024 at 10:36 PM AngeloGioacchino Del Regno <
> angelogioacchino.delregno@...labora.com> wrote:
> 
>> Il 13/03/24 14:51, Pin-yen Lin ha scritto:
>>> Although the minimum voltage listed on the GPU OPP table is 606250 uV,
>>> the actual requested voltage could be even lower when the MTK Smart
>>> Voltage Scaling (SVS) driver is enabled.
>>>
>>> Set the minimum voltage to 300000 uV because it's supported by the
>>> regulator.
>>>
>>> Fixes: 3183cb62b033 ("arm64: dts: mediatek: asurada: Add SPMI
>> regulators")
>>> Signed-off-by: Pin-yen Lin <treapking@...omium.org>
>>
>> Okay, that makes sense, I agree.
>>
>> ...but.
>>
>> The datasheet never mentions 0.3V as vmin - infact, it does mention that
>> the
>> vsel is selected as (0V +) 6250 * Vsel, but the brief spec says that for
>> the
>> standard configuration (in terms of HW), the Vmin is 0.4V and not 0.3.
>>
>> Reading through makes me think that it's not much about the buck providing
>> an
>> unstable output, but more about it starting to become inefficient under
>> that
>> value.
>>
>> This means that it is sensible to set, instead:
>>
>>          regulator-min-microvolt = <400000>;
>>
>> Also, this is repeated on multiple platforms: can you please perform the
>> same
>> change also on MT8183, MT8186 and MT8195?
>>
>> P.S.: For MT6358, the Vmin for VGPU is 0.5V :-)
>>
> 
> Thanks for checking! I'll update the values on other platforms as well.
> 
> I assume that we also want to update other mt6315 nodes listing 300000 uV
> as the min voltage, so I'll update them as well.
> 

Yes, didn't notice that, nice catch. Please do!

Cheers,
Angelo

>>
>>> ---
>>>
>>>    arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>> b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>> index 43d80334610a..5cc5100a7c40 100644
>>> --- a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>> +++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>> @@ -1448,7 +1448,7 @@ regulators {
>>>                        mt6315_7_vbuck1: vbuck1 {
>>>                                regulator-compatible = "vbuck1";
>>>                                regulator-name = "Vgpu";
>>> -                             regulator-min-microvolt = <606250>;
>>> +                             regulator-min-microvolt = <300000>;
>>>                                regulator-max-microvolt = <800000>;
>>>                                regulator-enable-ramp-delay = <256>;
>>>                                regulator-allowed-modes = <0 1 2>;
>>
>>
>>
>