linux-kernel - Re: [PATCH 20/40] mmc: tegra: Add a workaround for tap value change glitch

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Message-ID: <20180809125804.GY21639@ulmo>
Date:   Thu, 9 Aug 2018 14:58:04 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Aapo Vienamo <avienamo@...dia.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Stefan Agner <stefan@...er.ch>, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org
Subject: Re: [PATCH 20/40] mmc: tegra: Add a workaround for tap value change
 glitch

On Wed, Aug 01, 2018 at 07:32:10PM +0300, Aapo Vienamo wrote:
> Add quirk to disable the card clock during configuration of the tap
> value in tegra_sdhci_set_tap() and issue sdhci_reset() after value
> change. This is a workaround to avoid propagation of a potential
> glitch caused by setting the tap value.
> 
> Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> ---
>  drivers/mmc/host/sdhci-tegra.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> index 3c10451..a2375ad 100644
> --- a/drivers/mmc/host/sdhci-tegra.c
> +++ b/drivers/mmc/host/sdhci-tegra.c
> @@ -47,6 +47,9 @@
>  #define SDHCI_MISC_CTRL_ENABLE_SDHCI_SPEC_300		0x20
>  #define SDHCI_MISC_CTRL_ENABLE_DDR50			0x200
>  
> +#define SDHCI_VNDR_TUN_CTRL0_0				0x1c0
> +#define SDHCI_VNDR_TUN_CTRL0_TUN_HW_TAP			0x20000
> +
>  #define SDHCI_TEGRA_AUTO_CAL_CONFIG			0x1e4
>  #define SDHCI_AUTO_CAL_START				BIT(31)
>  #define SDHCI_AUTO_CAL_ENABLE				BIT(29)
> @@ -68,6 +71,7 @@
>  #define NVQUIRK_ENABLE_DDR50				BIT(5)
>  #define NVQUIRK_HAS_PADCALIB				BIT(6)
>  #define NVQUIRK_NEEDS_PAD_CONTROL			BIT(7)
> +#define NVQUIRK_DIS_CARD_CLK_CONFIG_TAP			BIT(8)
>  
>  struct sdhci_tegra_soc_data {
>  	const struct sdhci_pltfm_data *pdata;
> @@ -499,12 +503,32 @@ static unsigned int tegra_sdhci_get_max_clock(struct sdhci_host *host)
>  
>  static void tegra_sdhci_set_tap(struct sdhci_host *host, unsigned int tap)
>  {
> +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> +	struct sdhci_tegra *tegra_host = sdhci_pltfm_priv(pltfm_host);
> +	const struct sdhci_tegra_soc_data *soc_data = tegra_host->soc_data;
> +	bool card_clk_enabled = false;
>  	u32 reg;
>  
> +	/*
> +	 * Touching the tap values is a bit tricky on some SoC generations.
> +	 * The quirk enables a workaround for a glitch that sometimes occurs if
> +	 * the tap values are changed.
> +	 */
> +
> +	if (soc_data->nvquirks & NVQUIRK_DIS_CARD_CLK_CONFIG_TAP)
> +		card_clk_enabled = tegra_sdhci_configure_card_clk(host, false);
> +
>  	reg = sdhci_readl(host, SDHCI_TEGRA_VENDOR_CLOCK_CTRL);
>  	reg &= ~SDHCI_CLOCK_CTRL_TAP_MASK;
>  	reg |= tap << SDHCI_CLOCK_CTRL_TAP_SHIFT;
>  	sdhci_writel(host, reg, SDHCI_TEGRA_VENDOR_CLOCK_CTRL);
> +
> +	if (soc_data->nvquirks & NVQUIRK_DIS_CARD_CLK_CONFIG_TAP &&
> +		    card_clk_enabled) {

This is weirdly aligned.

> +		udelay(1);

Can this also become a usleep_range()? I may be too paranoid about
this...

Thierry

> +		sdhci_reset(host, SDHCI_RESET_CMD | SDHCI_RESET_DATA);
> +		tegra_sdhci_configure_card_clk(host, card_clk_enabled);
> +	}
>  }
>  
>  static int tegra_sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)
> @@ -758,7 +782,8 @@ static const struct sdhci_pltfm_data sdhci_tegra210_pdata = {
>  static const struct sdhci_tegra_soc_data soc_data_tegra210 = {
>  	.pdata = &sdhci_tegra210_pdata,
>  	.nvquirks = NVQUIRK_NEEDS_PAD_CONTROL |
> -		    NVQUIRK_HAS_PADCALIB,
> +		    NVQUIRK_HAS_PADCALIB |
> +		    NVQUIRK_DIS_CARD_CLK_CONFIG_TAP,
>  };
>  
>  static const struct sdhci_pltfm_data sdhci_tegra186_pdata = {
> @@ -783,7 +808,8 @@ static const struct sdhci_pltfm_data sdhci_tegra186_pdata = {
>  static const struct sdhci_tegra_soc_data soc_data_tegra186 = {
>  	.pdata = &sdhci_tegra186_pdata,
>  	.nvquirks = NVQUIRK_NEEDS_PAD_CONTROL |
> -		    NVQUIRK_HAS_PADCALIB,
> +		    NVQUIRK_HAS_PADCALIB |
> +		    NVQUIRK_DIS_CARD_CLK_CONFIG_TAP,
>  };
>  
>  static const struct of_device_id sdhci_tegra_dt_match[] = {
> -- 
> 2.7.4
> 

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