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

[Stefan Agner <stefan@agner.ch>]

On 04.07.2018 17:07, Stefan Agner wrote:
> 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
> 
> 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: http://lkml.kernel.org/r/20180628081331.13051-1-stefan@agner.ch
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> ---

Btw, I still get the switching error once during boot-up:
  mmc1: Switching to 3.3V signalling voltage failed

This is due to the call from mmc_set_initial_signal_voltage. It is a bit
unfortunate since this is printed as a warning. Not sure if that could
be prevented somehow?

--
Stefan

>  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 */