RE: [PATCH v2] mmc: sdhci-esdhc-imx: allow 1.8V modes without 100/200MHz pinctrl states

[A.s. Dong]

> -----Original Message-----
> From: Stefan Agner [mailto:stefan@xxxxxxxx]
> Sent: Wednesday, July 4, 2018 11:08 PM
> To: adrian.hunter@xxxxxxxxx; ulf.hansson@xxxxxxxxxx
> Cc: Fabio Estevam <fabio.estevam@xxxxxxx>; Bough Chen
> <haibo.chen@xxxxxxx>; A.s. Dong <aisheng.dong@xxxxxxx>;
> michael@xxxxxxxxxxxxxxxxxxxx; rmk+kernel@xxxxxxxxxxxxxxx; linux-
> mmc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Stefan Agner
> <stefan@xxxxxxxx>
> Subject: [PATCH v2] mmc: sdhci-esdhc-imx: allow 1.8V modes without
> 100/200MHz pinctrl states
> 
> If pinctrl nodes for 100/200MHz are missing, the controller should not select
> any mode which need signal frequencies 100MHz or higher.
> To prevent such speed modes the driver currently uses the quirk flag
> SDHCI_QUIRK2_NO_1_8_V. This works nicely for SD cards since 1.8V signaling
> is required for all faster modes and slower modes use 3.3V signaling only.
> 
> However, there are eMMC modes which use 1.8V signaling and run below
> 100MHz, e.g. DDR52 at 1.8V. With using SDHCI_QUIRK2_NO_1_8_V this
> mode is prevented. When using a fixed 1.8V regulator as vqmmc-supply the
> stack has no valid mode to use. In this tenuous situation the kernel
> continuously prints voltage switching errors:
>   mmc1: Switching to 3.3V signalling voltage failed
> 

>From current code, the NO_1_8_V quirk seems like only affect sd card.
The 1.8v timing is still allowed for eMMC 1_8V DDR.
See below:
        if ((mmc->caps & (MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 |
                          MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR104 |
                          MMC_CAP_UHS_DDR50 | MMC_CAP_1_8V_DDR)) ||
            (mmc->caps2 & (MMC_CAP2_HS200_1_8V_SDR | MMC_CAP2_HS400_1_8V)))
                host->flags |= SDHCI_SIGNALING_180;

Due to i have no board to try that case, can you please help detail more on how the
eMMC DDR52 is blocked due to that quirk?

Regards
Dong Aisheng

> Avoid using SDHCI_QUIRK2_NO_1_8_V and prevent faster modes by altering
> the SDHCI capability register. With that the stack is able to select 1.8V modes
> even if no faster pinctrl states are available:
>   # cat /sys/kernel/debug/mmc1/ios
>   ...
>   timing spec:    8 (mmc DDR52)
>   signal voltage: 1 (1.80 V)
>   ...
> 
> Link:
> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flkml
> .kernel.org%2Fr%2F20180628081331.13051-1-
> stefan%40agner.ch&amp;data=02%7C01%7Caisheng.dong%40nxp.com%7Ca
> 32bdbdb4e854ed1a49008d5e1bfeae2%7C686ea1d3bc2b4c6fa92cd99c5c30163
> 5%7C0%7C0%7C636663136759720275&amp;sdata=%2F2gJ%2BA0fHCzzUehD7
> 9knsfy3WMj4Okp%2BcxXB70MI5y8%3D&amp;reserved=0
> Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
> ---
>  drivers/mmc/host/sdhci-esdhc-imx.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-
> esdhc-imx.c
> index 20a420b765b3..e96d969ab2c3 100644
> --- a/drivers/mmc/host/sdhci-esdhc-imx.c
> +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
> @@ -312,6 +312,15 @@ static u32 esdhc_readl_le(struct sdhci_host *host,
> int reg)
> 
>  			if (imx_data->socdata->flags & ESDHC_FLAG_HS400)
>  				val |= SDHCI_SUPPORT_HS400;
> +
> +			/*
> +			 * Do not advertise faster UHS modes if there are no
> +			 * pinctrl states for 100MHz/200MHz.
> +			 */
> +			if (IS_ERR_OR_NULL(imx_data->pins_100mhz) ||
> +			    IS_ERR_OR_NULL(imx_data->pins_200mhz))
> +				val &= ~(SDHCI_SUPPORT_SDR50 |
> SDHCI_SUPPORT_DDR50
> +					 | SDHCI_SUPPORT_SDR104 |
> SDHCI_SUPPORT_HS400);
>  		}
>  	}
> 
> @@ -1157,18 +1166,6 @@ sdhci_esdhc_imx_probe_dt(struct
> platform_device *pdev,
> 
> 	ESDHC_PINCTRL_STATE_100MHZ);
>  		imx_data->pins_200mhz = pinctrl_lookup_state(imx_data-
> >pinctrl,
> 
> 	ESDHC_PINCTRL_STATE_200MHZ);
> -		if (IS_ERR(imx_data->pins_100mhz) ||
> -				IS_ERR(imx_data->pins_200mhz)) {
> -			dev_warn(mmc_dev(host->mmc),
> -				"could not get ultra high speed state, work on
> normal mode\n");
> -			/*
> -			 * fall back to not supporting uhs by specifying no
> -			 * 1.8v quirk
> -			 */
> -			host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
> -		}
> -	} else {
> -		host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
>  	}
> 
>  	/* call to generic mmc_of_parse to support additional capabilities */
> --
> 2.18.0