Re: BUG 4.4rc-4: wrong eMMC signaling voltage reported

From: Fabio Estevam <festevam@gmail.com>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Holger Schurig <holgerschurig@gmail.com>,
	linux-mmc <linux-mmc@vger.kernel.org>
Subject: Re: BUG 4.4rc-4: wrong eMMC signaling voltage reported
Date: Tue, 22 Dec 2015 07:39:29 -0200	[thread overview]
Message-ID: <CAOMZO5B3WpJRYD7CRX54G0NeWj_BxNL5dB+KjG=YttDHQTx3vQ@mail.gmail.com> (raw)
In-Reply-To: <CAPDyKFoQqQFmPwrnCeJBcz=mnzW8zbWb5i7bc64oo7bN_113zQ@mail.gmail.com>

Hi Ulf and Holger,

On Thu, Dec 17, 2015 at 2:10 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:

> The no-1-8-v is a somewhat broken DT binding. I advise people to not
> use any more.
> Depending on the sdhci variant it have different meanings.
>
> I guess you are using the sdhci-esdhc-imx variant, which means
> no-1-8-v will disable UHS modes for SD-cards (those requiring 1.8V
> signal voltage). It has no impact on (e)MMC.
>
> As the host driver announces support for MMC_CAP_1_8V_DDR, that's what
> the mmc core will try to use. Actually the mmc core will first try
> 1.8V and if it fails, go for 3.3V.
>
> Likely, sdhci_do_start_signal_voltage_switch() will success to write
> the corresponding registers to change the signal voltage to 1.8V,
> which makes the mmc core believe it was a success.
>
> *If* your statement around that your HW don't support 1.8V signal
> voltage, we should perhaps add new mmc cap as currently we don't have
> a "MMC_CAP_3_3V_DDR". Although, you need to convince on that, because
> my experience tells that quite many has misunderstood the HW design in
> this regard.

Yes, I have added a 'MMC_CAP_3_3V_ONLY_DDR' in this proposal to fix
the same issue as Holger describes:
http://www.spinics.net/lists/linux-mmc/msg32285.html

,but it seems you were not happy with such approach at that time.
Unfortunately, I was not able to rework it.

Regards,

Fabio Estevam