Re: [PATCH 4/8] mmc: tegra: Implement HS400 delay line calibration

From: Thierry Reding <thierry.reding@gmail.com>
To: Aapo Vienamo <avienamo@nvidia.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Mikko Perttunen <mperttunen@nvidia.com>,
	linux-mmc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] mmc: tegra: Implement HS400 delay line calibration
Date: Thu, 9 Aug 2018 13:48:05 +0200	[thread overview]
Message-ID: <20180809114805.GM21639@ulmo> (raw)
In-Reply-To: <1533650404-18125-5-git-send-email-avienamo@nvidia.com>

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On Tue, Aug 07, 2018 at 05:00:00PM +0300, Aapo Vienamo wrote:
> Implement HS400 specific delay line calibration procedure.
> 
> Signed-off-by: Aapo Vienamo <avienamo@nvidia.com>
> ---
>  drivers/mmc/host/sdhci-tegra.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)

Should this be before the previous patch in order to make sure the
calibration is performed as soon as the feature is available. This is
counting beans I guess, but it is technically possible for someone to
get everything up to patch 3/8 and then get the corresponding changes
in the DTS files to enable the mode and then have HS400 enabled without
this calibration.

Thierry

> 
> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> index d81143b..d0b68b7 100644
> --- a/drivers/mmc/host/sdhci-tegra.c
> +++ b/drivers/mmc/host/sdhci-tegra.c
> @@ -56,6 +56,12 @@
>  #define SDHCI_MISC_CTRL_ENABLE_SDHCI_SPEC_300		0x20
>  #define SDHCI_MISC_CTRL_ENABLE_DDR50			0x200
>  
> +#define SDHCI_TEGRA_VENDOR_DLLCAL_CFG			0x1b0
> +#define SDHCI_TEGRA_DLLCAL_CALIBRATE			BIT(31)
> +
> +#define SDHCI_TEGRA_VENDOR_DLLCAL_STA			0x1bc
> +#define SDHCI_TEGRA_DLLCAL_STA_ACTIVE			BIT(31)
> +
>  #define SDHCI_VNDR_TUN_CTRL0_0				0x1c0
>  #define SDHCI_VNDR_TUN_CTRL0_TUN_HW_TAP			0x20000
>  
> @@ -584,6 +590,24 @@ static void tegra_sdhci_set_dqs_trim(struct sdhci_host *host, u8 val)
>  	sdhci_writel(host, reg, SDHCI_TEGRA_VENDOR_CAP_OVERRIDES);
>  }
>  
> +static void tegra_sdhci_hs400_dll_cal(struct sdhci_host *host)
> +{
> +	u32 reg;
> +	int err;
> +
> +	reg = sdhci_readl(host, SDHCI_TEGRA_VENDOR_DLLCAL_CFG);
> +	reg |= SDHCI_TEGRA_DLLCAL_CALIBRATE;
> +	sdhci_writel(host, reg, SDHCI_TEGRA_VENDOR_DLLCAL_CFG);

Is this self-clearing? Or do we need to clear it manually in order for
a subsequent calibration procedure to succeed?

Thierry

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