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

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Date:   Thu, 11 Nov 2021 14:56:19 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chun-Jie Chen <chun-jie.chen@...iatek.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] soc: mediatek: Add support always on flag

Il 02/11/21 08:20, 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>
> ---
>   drivers/soc/mediatek/mt8195-pm-domains.h | 2 +-
>   drivers/soc/mediatek/mtk-pm-domains.c    | 2 ++
>   drivers/soc/mediatek/mtk-pm-domains.h    | 1 +
>   3 files changed, 4 insertions(+), 1 deletion(-)
> 

Hello Chunfeng,
what are are the side effects on the USB2 PHY? Can you please expand?

Also, wouldn't it be possible to also reset the USB2 PHY when resetting the t-phy
in order to get it back up and running?

Moreover, as for the USB3.2 hardware limitation... I would say that this is more
like something that has to be accounted for in the USB driver, instead of the PM
domains driver... unless there's some reason that stops you from doing that?

Thanks,
- Angelo