From mboxrd@z Thu Jan  1 00:00:00 1970
From: Fabio Estevam <festevam@gmail.com>
Subject: Re: [PATCH v2] mmc: core: Do not set mmc voltage to 1.8V when
 'no-1-8-v' is present
Date: Mon, 15 Jun 2015 09:49:33 -0300
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To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Dong Aisheng <aisheng.dong@freescale.com>, Kevin Lemoi <kevin.lemoi@savant.com>, Otavio Salvador <otavio@ossystems.com.br>, Sascha Hauer <kernel@pengutronix.de>, Russell King - ARM Linux <linux@arm.linux.org.uk>, "Dong, Chuanxiao" <chuanxiao.dong@intel.com>, linux-mmc <linux-mmc@vger.kernel.org>, Fabio Estevam <fabio.estevam@freescale.com>

On Mon, Jun 15, 2015 at 9:23 AM, Fabio Estevam <festevam@gmail.com> wrote:
> Hi Ulf,
>
> On Mon, Jun 15, 2015 at 9:08 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
>> What card (eMMC, SD, MMC) and which host driver is being used here?
>
> It is an eMMC and the host driver is sdhci-esdhc-imx.c.
>
>>> --- a/drivers/mmc/core/host.c
>>> +++ b/drivers/mmc/core/host.c
>>> @@ -527,6 +527,8 @@ int mmc_of_parse(struct mmc_host *host)
>>>                 host->caps2 |= MMC_CAP2_HS400_1_8V | MMC_CAP2_HS200_1_8V_SDR;
>>>         if (of_find_property(np, "mmc-hs400-1_2v", &len))
>>>                 host->caps2 |= MMC_CAP2_HS400_1_2V | MMC_CAP2_HS200_1_2V_SDR;
>>> +       if (of_find_property(np, "no-1-8-v", &len))
>>> +               host->caps2 |= MMC_CAP_3_3V_ONLY_DDR;
>>
>> Do you intend to use 3.3V as the I/O voltage level for an eMMCs
>> running in DDR mode? Isn't that violation of the eMMC spec?
>
> Yes, I would like to use 3.3V as the I/O voltage level for an eMMC in DDR mode.
>
> This was the behaviour prior to 312449efd16bb0, which I would like to
> keep so that our custom board based on mx6sl could work. It works fine
> with 3.14 kernel, but not on 4.1-rc due to the fact that the board
> cannot provide 1.8V level, hence 'no-1-8-v' property is passed in the
> device tree. With this patch applied 3.3V is applied and the eMMC can
> successfully operate in 3.3V DDR mode.

Also, looked at the eMMC spec and the only restriction I saw about
using 3.3V voltage is with HS200 or HS400 devices:

"VCCQ (I/O) 3.3 V range is not supported in either HS200 or HS400 devices"

Regards,

Fabio Estevam