linux-kernel - Re: [v3 PATCH] soc: mediatek: Add support always on flag

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Message-ID: <2af6726c-5ff0-07c9-05de-1a67a7358ba2@collabora.com>
Date:   Mon, 23 May 2022 13:11:27 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Min Guo <min.guo@...iatek.com>,
        MandyJH Liu <mandyjh.liu@...iatek.com>,
        Eddie Hung <eddie.hung@...iatek.com>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [v3 PATCH] soc: mediatek: Add support always on flag

Il 20/05/22 05:03, Chunfeng Yun ha scritto:
> There is a t-phy shared by PCIe and USB3 on mt8195, if the t-phy is
> used by PCIe, when power off its mtcmos, need software reset it
> (workaround way, usually hardware do it, but has an issue on mt8195),
> but it has side effect to USB2 phy(works with USB3 phy to support
> USB3.2 Gen1), so add support GENPD_FLAG_ALWAYS_ON flag, and make its
> power always on;
> Another reason is that USB3.2 Gen1/2 need keep power always on when
> support runtime-pm due to hardware limitation until now;
> 
> Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>

All these quirks are making this situation very unfortunate. I don't
really like setting GENPD_FLAG_ALWAYS_ON, but I recognize that there's
nothing else to do to fix that.

After all, this power domain is going to stay up for >=95% of the time
anyway even if we handle this in the various drivers instead of setting
it as always on and.. in the end, it's not worth the effort if we're
saving power in the order of a few microamps per hour.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>