linux-kernel - Re: [PATCH v2] arm64: dts: allwinner: h6: add eMMC voltage property for Beelink GS1

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Date:   Mon, 5 Oct 2020 11:21:45 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Clément Péron <peron.clem@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64: dts: allwinner: h6: add eMMC voltage property
 for Beelink GS1

Hi Clément,

On Sat, Oct 03, 2020 at 11:20:01AM +0200, Clément Péron wrote:
> Sunxi MMC driver can't distinguish at runtime what's the I/O voltage
> for HS200 mode.

Unfortunately, that's not true (or at least, that's not related to your patch).

> Add a property in the device-tree to notify MMC core about this
> configuration.
> 
> Fixes: 089bee8dd119 ("arm64: dts: allwinner: h6: Introduce Beelink GS1 board")
> Signed-off-by: Clément Péron <peron.clem@...il.com>
> ---
>  arch/arm64/boot/dts/allwinner/sun50i-h6-beelink-gs1.dts | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h6-beelink-gs1.dts b/arch/arm64/boot/dts/allwinner/sun50i-h6-beelink-gs1.dts
> index 049c21718846..3f20d2c9bbbb 100644
> --- a/arch/arm64/boot/dts/allwinner/sun50i-h6-beelink-gs1.dts
> +++ b/arch/arm64/boot/dts/allwinner/sun50i-h6-beelink-gs1.dts
> @@ -145,6 +145,7 @@ &mmc2 {
>  	vqmmc-supply = <&reg_bldo2>;
>  	non-removable;
>  	cap-mmc-hw-reset;
> +	mmc-hs200-1_8v;
>  	bus-width = <8>;
>  	status = "okay";
>  };

I'm not really sure what you're trying to fix here, but as far as MMC
goes, eMMC's can support io voltage of 3.3, 1.8 and 1.2V. Modes up until
HS DDR (50MHz in DDR) will use an IO voltage of 3.3V, higher speed modes
(HS200 and HS400) supporting 1.8V and 1.2V.

The mmc-hs200-1_8v property states that the MMC controller supports the
HS200 mode at 1.8V. Now, I can only assume that since BLDO2 is set up at
1.8V then otherwise, the MMC core will rightfully decide to use the
highest supported mode. In this case, since the driver sets it, it would
be HS-DDR at 3.3V, which won't work with that fixed regulator.

I can only assume that enabling HS200 at 1.8V only fixes the issue you
have because otherwise it would use HS-DDR at 3.3V, ie not actually
fixing the issue but sweeping it under the rug.

Trying to add mmc-ddr-1_8v would be a good idea

Maxime

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