linux-kernel - Re: [PATCH v2] mmc: sdhci-tegra: Fix switch to HS400ES mode

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Date:   Thu, 2 Dec 2021 16:35:00 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Prathamesh Shete <pshete@...dia.com>, ulf.hansson@...aro.org,
        thierry.reding@...il.com, jonathanh@...dia.com,
        p.zabel@...gutronix.de, linux-mmc@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     anrao@...dia.com, smangipudi@...dia.com
Subject: Re: [PATCH v2] mmc: sdhci-tegra: Fix switch to HS400ES mode

On 02/12/2021 15:49, Prathamesh Shete wrote:
> When CMD13 is sent after switching to HS400ES mode, the bus
> is operating at either MMC_HIGH_26_MAX_DTR or MMC_HIGH_52_MAX_DTR.
> To meet Tegra SDHCI requirement at HS400ES mode, force SDHCI
> interface clock to MMC_HS200_MAX_DTR (200 MHz) so that host
> controller CAR clock and the interface clock are rate matched.
> 
> Signed-off-by: Prathamesh Shete <pshete@...dia.com>
> ---
>  drivers/mmc/host/sdhci-tegra.c | 43 ++++++++++++++++++++--------------
>  1 file changed, 26 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> index 387ce9cdbd7c..ca261cce9b37 100644
> --- a/drivers/mmc/host/sdhci-tegra.c
> +++ b/drivers/mmc/host/sdhci-tegra.c
> @@ -354,23 +354,6 @@ static void tegra_sdhci_set_tap(struct sdhci_host *host, unsigned int tap)
>  	}
>  }
>  
> -static void tegra_sdhci_hs400_enhanced_strobe(struct mmc_host *mmc,
> -					      struct mmc_ios *ios)
> -{
> -	struct sdhci_host *host = mmc_priv(mmc);
> -	u32 val;
> -
> -	val = sdhci_readl(host, SDHCI_TEGRA_VENDOR_SYS_SW_CTRL);
> -
> -	if (ios->enhanced_strobe)
> -		val |= SDHCI_TEGRA_SYS_SW_CTRL_ENHANCED_STROBE;
> -	else
> -		val &= ~SDHCI_TEGRA_SYS_SW_CTRL_ENHANCED_STROBE;
> -
> -	sdhci_writel(host, val, SDHCI_TEGRA_VENDOR_SYS_SW_CTRL);
> -
> -}
> -
>  static void tegra_sdhci_reset(struct sdhci_host *host, u8 mask)
>  {
>  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> @@ -791,6 +774,32 @@ static void tegra_sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
>  	}
>  }
>  
> +static void tegra_sdhci_hs400_enhanced_strobe(struct mmc_host *mmc,
> +					      struct mmc_ios *ios)
> +{
> +	struct sdhci_host *host = mmc_priv(mmc);
> +	u32 val;
> +
> +	val = sdhci_readl(host, SDHCI_TEGRA_VENDOR_SYS_SW_CTRL);
> +
> +	if (ios->enhanced_strobe)
> +		val |= SDHCI_TEGRA_SYS_SW_CTRL_ENHANCED_STROBE;
> +	else
> +		val &= ~SDHCI_TEGRA_SYS_SW_CTRL_ENHANCED_STROBE;
> +
> +	sdhci_writel(host, val, SDHCI_TEGRA_VENDOR_SYS_SW_CTRL);
> +
> +	/*
> +	 * When CMD13 is sent from mmc_select_hs400es() after
> +	 * switching to HS400ES mode, the bus is operating at
> +	 * either MMC_HIGH_26_MAX_DTR or MMC_HIGH_52_MAX_DTR.
> +	 * To meet Tegra SDHCI requirement at HS400ES mode, force SDHCI
> +	 * interface clock to MMC_HS200_MAX_DTR (200 MHz) so that host
> +	 * controller CAR clock and the interface clock are rate matched.

Still doesn't explain why you want to set MMC_HS200_MAX_DTR when
ios->enhanced_strobe is false e.g. mmc_set_initial_state()

> +	 */
> +	tegra_sdhci_set_clock(host, MMC_HS200_MAX_DTR);
> +}
> +
>  static unsigned int tegra_sdhci_get_max_clock(struct sdhci_host *host)
>  {
>  	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>