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Message-ID: <d1bdf9a6-3082-4076-99de-e49d59843244@collabora.com>
Date: Wed, 13 Mar 2024 15:36:50 +0100
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Subject: Re: [PATCH] arm64: dts: mediatek: mt8192-asurada: Update min voltage
 constraint for Vgpu
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To: Pin-yen Lin <treapking@chromium.org>,
 Matthias Brugger <matthias.bgg@gmail.com>
Cc: Chen-Yu Tsai <wenst@chromium.org>, linux-kernel@vger.kernel.org,
 linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org,
 =?UTF-8?Q?N=C3=ADcolas_F_=2E_R_=2E_A_=2E_Prado?= <nfraprado@collabora.com>,
 devicetree@vger.kernel.org
References: <20240313135157.98989-1-treapking@chromium.org>
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
In-Reply-To: <20240313135157.98989-1-treapking@chromium.org>
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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@chromium.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 :-)

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>;