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From:   Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [RFC PATCH V3 13/21] mmc: sdhci: UHS-II support, skip
 signal_voltage_switch()
To:     Ben Chuang <benchuanggli@gmail.com>, ulf.hansson@linaro.org
Cc:     linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
        ben.chuang@genesyslogic.com.tw, takahiro.akashi@linaro.org,
        greg.tu@genesyslogic.com.tw
References: <20200710111104.29616-1-benchuanggli@gmail.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Date:   Fri, 21 Aug 2020 17:09:01 +0300
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On 10/07/20 2:11 pm, Ben Chuang wrote:
> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> 
> sdhci_start_signal_voltage_switch() should be called only in UHS-I mode,
> and not for UHS-II mode.
> 
> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> ---
>  drivers/mmc/host/sdhci.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 5511649946b9..7f2537648a08 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2623,8 +2623,13 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
>  	/*
>  	 * Signal Voltage Switching is only applicable for Host Controllers
>  	 * v3.00 and above.
> +	 * But for UHS2, the signal voltage is supplied by vdd2 which is
> +	 * already 1.8v so no voltage switch required.
>  	 */
> -	if (host->version < SDHCI_SPEC_300)
> +	if (host->version < SDHCI_SPEC_300 ||
> +	    (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2) &&
> +	     host->version >= SDHCI_SPEC_400 &&
> +	     host->mmc->flags & MMC_UHS2_SUPPORT))

Please look at hooking ->start_signal_voltage_switch() instead


>  		return 0;
>  
>  	ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
>