linux-kernel - Re: [PATCH v4] arm64: dts: rockchip: Fix SD card init on rk3399-nanopi4

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Message-Id: <3912A668-9F73-40FD-8993-5060F632238A@kohlschutter.com>
Date:   Sat, 16 Jul 2022 02:24:49 +0200
From:   Christian Kohlschütter 
        <christian@...lschutter.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     wens@...nel.org, Heiko Stübner <heiko@...ech.de>,
        Markus Reichl <m.reichl@...etechno.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux MMC List <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH v4] arm64: dts: rockchip: Fix SD card init on
 rk3399-nanopi4

>> 
>>> There may well be another bug slumbering in the codebase that is circumvented by 1. adding a delay in the code and 2. not turning the regulator off upon shutdown.
>> 
>> Yes, it seems suboptimal that the regulator core allows this glitch where an always-on regulator which is already on gets turned off at all, but I guess that's its own problem. In the meantime, off-on-delay-us sounds like the most likely property to bandage this locally. I'm seeing a fall time in the order of milliseconds (attached), so we'd probably want a fair chunk of that to be safe.
>> 
>> Robin.<SDS00003.png>
> 
> I think we have a way where there's no need to pick a delay value that may ultimately not work in all cases.
> Following up with "[PATCH] regulator: core: Resolve supply name earlier to prevent double-init" [1]
> 
> Thank you so much for helping me getting that far! It would be great if you'd keep following the thread.
> 
> Best,
> Christian
> 
> [1] https://www.spinics.net/lists/kernel/msg4440365.html

@Robin,

oddly enough, setting off-on-delay-us with values of up to a second (1000000 us) still results in failed inits.
I hope we can find another bandage until the regular-core patch gets merged.