linux-kernel - Re: [PATCH v4 0/1] i2c: mediatek: add runtime PM operations and bus regulator control

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Message-ID: <ec77bb9478cd86a6737b92135170064970925b3c.camel@mediatek.com>
Date: Tue, 4 Mar 2025 08:37:27 +0000
From: Zoie Lin (林禹妡) <Zoie.Lin@...iatek.com>
To: Qii Wang (王琪) <Qii.Wang@...iatek.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	"matthias.bgg@...il.com" <matthias.bgg@...il.com>, "andi.shyti@...nel.org"
	<andi.shyti@...nel.org>
CC: Teddy Chen (陳乾元) <Teddy.Chen@...iatek.com>,
	Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>,
	Shunchang Wang (王舜昌)
	<ot_shunchang.wang@...iatek.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>,
	Joseph-CC Chang (張欽洲)
	<Joseph-CC.Chang@...iatek.com>, "linux-mediatek@...ts.infradead.org"
	<linux-mediatek@...ts.infradead.org>, "linux-i2c@...r.kernel.org"
	<linux-i2c@...r.kernel.org>, Leilk Liu (刘磊)
	<Leilk.Liu@...iatek.com>
Subject: Re: [PATCH v4 0/1] i2c: mediatek: add runtime PM operations and bus
 regulator control


Hi Angelo,

Thank you for your suggestions regarding the autosuspend delay.

We understand the importance of balancing power efficiency and
responsiveness. Given the diversity of I2C devices connected
under each platform, it is indeed challenging to estimate an
appropriate delay time for testing.

Therefore, we would like to proceed with your initial suggestion
and set the autosuspend delay to 250ms. Based on our preliminary
tests, this adjustment appears to be a practical solution across 
our existing platforms.

Thank you.

Best regards,
Zoie


On Thu, 2025-02-13 at 12:57 +0100, AngeloGioacchino Del Regno wrote:
> 
> 
> Turning on and off regulators at start of transfer and end of
> transfer respectively
> is very expensive and, while it makes sense for power efficiency of
> the controller,
> it doesn't make sense for:
> 
>   1. Responsiveness (latency); and
>   2. Platform power efficiency at a whole.
> 
> As a start, just set the autosuspend delay to 250ms; this gives you
> at least time
> to bring up clocks and regulators and usually finish a transfer at
> 400KHz, giving
> you the chance to also get some more requests before autosuspend
> decides to, well,
> auto..suspend the device.
> 
> The right way of choosing an autosuspend delay a bit more precisely,
> though, for
> this device, would be to check the bus speed and calculate the
> autosuspend time
> accordingly.
> 
> Cheers,
> Angelo
> 
> 
>