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

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Message-ID: <f7453c57-d921-a789-75f6-c837ca50187c@collabora.com>
Date:   Tue, 7 Mar 2023 10:47:39 +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 10:44, Chen-Yu Tsai ha scritto:
> On Tue, Mar 7, 2023 at 5:30 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@...labora.com> wrote:
>>
>> 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?
> 
> It works for some reason. Maybe it's a bug in the coupler. Either way I
> think it works, even though the numbers might be a bit off. We can revisit
> it later.
> 
> Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>


Thanks!

Angelo