linux-kernel - Re: [PATCH v2] mmc: sdhci-esdhc-imx: allow 1.8V modes without 100/200MHz pinctrl states

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Message-ID: <CAPDyKFovmZxR=Bv0rogas+RTkzkSwbcyRyu1pD4m0LYvExbY8A@mail.gmail.com>
Date:   Thu, 5 Jul 2018 13:23:13 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Haibo Chen <haibo.chen@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: sdhci-esdhc-imx: allow 1.8V modes without
 100/200MHz pinctrl states

On 4 July 2018 at 17:07, Stefan Agner <stefan@...er.ch> wrote:
> If pinctrl nodes for 100/200MHz are missing, the controller should
> not select any mode which need signal frequencies 100MHz or higher.
> To prevent such speed modes the driver currently uses the quirk flag
> SDHCI_QUIRK2_NO_1_8_V. This works nicely for SD cards since 1.8V
> signaling is required for all faster modes and slower modes use 3.3V
> signaling only.
>
> However, there are eMMC modes which use 1.8V signaling and run below
> 100MHz, e.g. DDR52 at 1.8V. With using SDHCI_QUIRK2_NO_1_8_V this
> mode is prevented. When using a fixed 1.8V regulator as vqmmc-supply
> the stack has no valid mode to use. In this tenuous situation the
> kernel continuously prints voltage switching errors:
>   mmc1: Switching to 3.3V signalling voltage failed
>
> Avoid using SDHCI_QUIRK2_NO_1_8_V and prevent faster modes by
> altering the SDHCI capability register. With that the stack is able
> to select 1.8V modes even if no faster pinctrl states are available:
>   # cat /sys/kernel/debug/mmc1/ios
>   ...
>   timing spec:    8 (mmc DDR52)
>   signal voltage: 1 (1.80 V)
>   ...
>
> Link: http://lkml.kernel.org/r/20180628081331.13051-1-stefan@agner.ch
> Signed-off-by: Stefan Agner <stefan@...er.ch>

I am fine with this. Do you want me to apply this for now, to get it tested?

I guess its also material for stable and as fix?

In regards to the printed warning, it sounds to me like a different
issue, which we can solve on top. Right?

[...]

Kind regards
Uffe