linux-kernel - Re: [PATCH] mmc: meson: initial ocr available by default value

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Date:   Mon, 13 Dec 2021 20:02:50 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        "rong.chen@...ogic.com" <rong.chen@...ogic.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        "--to=1131046452" <--to=1131046452@...com>,
        45581586 <45581586@...com>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic <linux-amlogic@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: meson: initial ocr available by default value

On Mon, Dec 13, 2021 at 2:25 PM Jerome Brunet <jbrunet@...libre.com> wrote:
>
>
> On Mon 13 Dec 2021 at 19:50, "rong.chen@...ogic.com" <rong.chen@...ogic.com> wrote:
>
> > Hello,
> > If 3.3V always-on power source for vmmc is supplied by hardware boards fixed, don't need regulator in software, so  .dts unnecessary the link between regulator
> > and MMC controller vmmc/vqmmc.
>
> Controllable or not, your vmmc/vqmmc regulators should be described in
> DT.
I agree with Jerome. Here are the two reasons why I think that it's
best to describe these regulators in device-tree:
- device-tree is there to describe the hardware. It's especially
useful for non-discoverable information (USB and PCI IDs are
discoverable examples), for example: voltage supply of an MMC
controller, UART IRQ line, ...
- reviewing board.dts would be a lot harder if we rely on defaults
(defaults which cannot be described in a device-tree schema). For
meson-g12a-radxa-zero.dts this means we could omit the vmmc/vqmmc
regulators for the SD card slot but we need them for the eMMC (because
vqmmc is fixed at 1.8V).


Best regards,
Martin