linux-kernel - Re: [PATCH v3 3/4] arm64: dts: apple: t8103: Add i2c nodes

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Date:   Fri, 26 Nov 2021 01:01:44 +0900
From:   "Hector Martin \"marcan\"" <marcan@...can.st>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     Janne Grunau <j@...nau.net>, Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/4] arm64: dts: apple: t8103: Add i2c nodes



On 2021年11月26日 0:50:28 JST, Linus Walleij <linus.walleij@...aro.org> wrote:
>On Wed, Nov 24, 2021 at 6:42 AM Hector Martin <marcan@...can.st> wrote:
>
>> Pulling down an I2C bus between transactions is not legal; the idle
>> state has to be high.
>
>Oh right.
>
>> Apple are actually not very good at configuring GPIOs for power saving;
>> e.g. the I/Os for that unused i2c bus still have their input buffers
>> turned on, which is a waste of power. If they wanted to save the
>> smallest drop of power they'd turn that off. But the effect of this is
>> so trivial it probably makes no difference in the context of a laptop,
>> nevermind a desktop like the Mac Mini.
>
>Hm that's true. The saying is that 99% is the backlight, the remaining 1% isn't
>so significant after that.

>From watching a USB power meter plugged into the MacBook Air, I can say the backlight is about 70% :-)

Then again, the new MBPs have LED matrix backlit screens... so suddenly dark themes are more efficient again! I should measure that one, see how much power changing themes saves.

-- 
Hector Martin "marcan" (marcan@...can.st)
Public key: https://mrcn.st/pub