linux-kernel - Re: [PATCH v2] mmc: sunxi-mmc: check ocr

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Date:   Wed, 12 Jan 2022 10:34:15 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Michael Wu <michael@...winnertech.com>
Cc:     ulf.hansson@...aro.org, wens@...e.org, samuel@...lland.org,
        andre.przywara@....com, jernej.skrabec@...il.com,
        linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mmc: sunxi-mmc: check ocr_avail on resource request

Hi,

On Tue, Jan 04, 2022 at 02:03:25PM +0800, Michael Wu wrote:
> Some platforms have no regulator, discrete power devices are used instead.

Is it really the case? vmmc at least should be mandatory so a platform
not having a regulator would violate the binding itself.

> However, sunxi_mmc_probe does not catch this exception when regulator is
> absent in DTS. This leads to sd or eMMC init failure.

This will still happen with your patch though?

> To solve this, a fixed vmmc regulator must be hooked up in DTS, like this:
> reg_dummy_vmmc: dummy_vmmc {
> 	compatible = "regulator-fixed";
> 	regulator-name = "dummy-vmmc";
> 	regulator-min-microvolt = <3300000>;
> 	regulator-max-microvolt = <3300000>;
> };
> 
> mmc0:mmc@...0000 {
> 	compatible = "allwinner,sun50i-a100-emmc";
> 	device_type = "mmc0";
> 	vmmc-supply = <&reg_dummy_vmmc>;
> }
> 
> In this patch, we print an error message and abort the probe process if
> the regulator is not specified in DTS.

I'm fine with the patch itself, but it's really not clear to me what
situation is being fixed or improved here.

You're first mentioning that this is fixing the driver probing even if a
regulator is absent, but then states (rightfully) that in such a case we
should use a fixed regulator. So we should always have a regulator then?

I assume that you want the driver to properly error out instead of going
on if either a regulator is missing or if its voltages are out of range?

If the former, then we should probably check if host->mmc->supply.vmmc
returned an error. If the latter, then yes, checking ocr_avail is
probably fine but we should make it clearer in the error message that
it's what it's about.

Maxime

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