linux-kernel - Re: [PATCH v4 12/19] arm64: dts: mediatek: mt8192-asurada: Couple VGPU and VSRAM

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Message-ID: <e1b9d901-421c-3509-c92a-c59d49ff2b0d@collabora.com>
Date:   Tue, 7 Mar 2023 10:30:04 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chen-Yu Tsai <wenst@...omium.org>
Cc:     matthias.bgg@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v4 12/19] arm64: dts: mediatek: mt8192-asurada: Couple
 VGPU and VSRAM_OTHER regulators

Il 07/03/23 10:24, Chen-Yu Tsai ha scritto:
> On Fri, Mar 3, 2023 at 12:09 PM Chen-Yu Tsai <wenst@...omium.org> wrote:
>>
>> On Thu, Mar 2, 2023 at 6:17 PM AngeloGioacchino Del Regno
>> <angelogioacchino.delregno@...labora.com> wrote:
>>>
>>> Il 02/03/23 11:03, Chen-Yu Tsai ha scritto:
>>>> On Wed, Mar 1, 2023 at 5:55 PM AngeloGioacchino Del Regno
>>>> <angelogioacchino.delregno@...labora.com> wrote:
>>>>>
>>>>> Add coupling for these regulators, as VSRAM_OTHER is used to power the
>>>>> GPU SRAM, and they have a strict voltage output relation to satisfy in
>>>>> order to ensure GPU stable operation.
>>>>> While at it, also add voltage constraint overrides for the GPU SRAM
>>>>> regulator "mt6359_vsram_others" so that we stay in a safe range of
>>>>> 0.75-0.80V.
>>>>>
>>>>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>>>>> ---
>>>>>    arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi | 9 +++++++++
>>>>>    1 file changed, 9 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>>>> index 8570b78c04a4..f858eca219d7 100644
>>>>> --- a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>>>> +++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>>>> @@ -447,6 +447,13 @@ &mt6359_vrf12_ldo_reg {
>>>>>           regulator-always-on;
>>>>>    };
>>>>>
>>>>> +&mt6359_vsram_others_ldo_reg {
>>>>> +       regulator-min-microvolt = <750000>;
>>>>> +       regulator-max-microvolt = <800000>;
>>>>> +       regulator-coupled-with = <&mt6315_7_vbuck1>;
>>>>> +       regulator-coupled-max-spread = <10000>;
>>>>
>>>> Looking again at the downstream OPP table, it seems there's no voltage
>>>> difference requirement. It only needs V_SRAM >= V_GPU. Same applies to
>>>> MT8195. Looks like only MT8183 and MT8186 need V_SRAM - V_GPU >= 10000.
>>>
>>> On MT8195 we don't need any regulator coupling. There, the GPU-SRAM voltage
>>> is fixed at .. I don't remember, 0.7V? - anyway - MT8195 doesn't need to
>>> scale the vsram.
>>
>> Looks like it's fixed at 0.75V. I guess we're Ok on MT8195.
>>
>>>>
>>>> Would setting max-spread to 0 work? I ask because with both regulator's
>>>> maximum voltage set to 0.8V, there's no way we can reach the highest
>>>> OPP.
>>>>
>>>
>>> No that doesn't work. I can raise the Vgpu max voltage to 0.88V to solve the
>>> issue right here and right now, or we can leave it like that and revisit it
>>> later.
>>>
>>> I would at this point go for setting mt6315_7_vbuck1's max-microvolt to
>>> 880000, as this is the maximum recommended voltage for the GPU as per the
>>> MT8192 datasheet, it would also make sense as we would be still describing
>>> the hardware in a correct manner.
>>>
>>> What do you think?
>>
>> If it's just to accommodate the coupler stuff, I say just set the maximum
>> at the lowest possible setting that satisfies the coupler constraint and
>> granularity of the regulator. The regulator does 6250 uV steps, so I guess
>> we could set the maximum at 812500 uV, with a comment stating the nominal
>> voltage of 800000 uV and that the extra 12500 uV is to workaround coupler
>> limitations.
>>
>> Does that sound OK?
> 
> Even without changing anything, the coupler seems to work OK:
> 
>   vsram_others                     1    1      0  normal   800mV
> 0mA   750mV   800mV
>      10006000.syscon:power-controller-domain   1
>           0mA     0mV     0mV
>   Vgpu                             2    2      0  normal   800mV
> 0mA   606mV   800mV
>      13000000.gpu-mali             1
> 0mA   800mV   800mV
>      10006000.syscon:power-controller-domain   1
>           0mA     0mV     0mV
> 
> Am I missing something?
> 

I don't think you are... I may be getting confused by all of the changesets
that I'm pushing at once.

Hence, is this commit fine as it is?

Regards,
Angelo