linux-kernel - Re: [PATCH 2/2] mmc: sdhci-of-at91: add DT property to enable calibration on full reset

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Date:   Fri, 11 Oct 2019 14:41:16 +0200
From:   Ludovic Desroches <ludovic.desroches@...rochip.com>
To:     Nicolas Ferre <nicolas.ferre@...rochip.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <robh+dt@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        <linux-kernel@...r.kernel.org>, <ulf.hansson@...aro.org>,
        <adrian.hunter@...el.com>
Subject: Re: [PATCH 2/2] mmc: sdhci-of-at91: add DT property to enable
 calibration on full reset

On Tue, Oct 08, 2019 at 02:34:32PM +0200, Nicolas Ferre wrote:
> Add a property to keep the analog calibration cell powered.
> This feature is specific to the Microchip SDHCI IP and outside
> of the standard SDHCI register map.
> 
> By always keeping it on, after a full reset sequence, we make sure
> that this feature is activated and not disabled.
> 
> We expose a hardware property to the DT as this feature can be used
> to adapt SDHCI behavior vs. how the SDCAL SoC pin is connected
> on the board.
> 
> Note that managing properly this property would reduce
> power consumption on some SAMA5D2 SiP revisions.
> 
> Signed-off-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@...rochip.com>

Thanks

Ludovic

> ---
>  drivers/mmc/host/sdhci-of-at91.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci-of-at91.c b/drivers/mmc/host/sdhci-of-at91.c
> index e7d1920729fb..9571c4a882a9 100644
> --- a/drivers/mmc/host/sdhci-of-at91.c
> +++ b/drivers/mmc/host/sdhci-of-at91.c
> @@ -27,6 +27,9 @@
>  #define SDMMC_CACR	0x230
>  #define		SDMMC_CACR_CAPWREN	BIT(0)
>  #define		SDMMC_CACR_KEY		(0x46 << 8)
> +#define SDMMC_CALCR	0x240
> +#define		SDMMC_CALCR_EN		BIT(0)
> +#define		SDMMC_CALCR_ALWYSON	BIT(4)
>  
>  #define SDHCI_AT91_PRESET_COMMON_CONF	0x400 /* drv type B, programmable clock mode */
>  
> @@ -35,6 +38,7 @@ struct sdhci_at91_priv {
>  	struct clk *gck;
>  	struct clk *mainck;
>  	bool restore_needed;
> +	bool cal_always_on;
>  };
>  
>  static void sdhci_at91_set_force_card_detect(struct sdhci_host *host)
> @@ -116,10 +120,17 @@ static void sdhci_at91_set_uhs_signaling(struct sdhci_host *host,
>  
>  static void sdhci_at91_reset(struct sdhci_host *host, u8 mask)
>  {
> +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> +	struct sdhci_at91_priv *priv = sdhci_pltfm_priv(pltfm_host);
> +
>  	sdhci_reset(host, mask);
>  
>  	if (host->mmc->caps & MMC_CAP_NONREMOVABLE)
>  		sdhci_at91_set_force_card_detect(host);
> +
> +	if (priv->cal_always_on && (mask & SDHCI_RESET_ALL))
> +		sdhci_writel(host, SDMMC_CALCR_ALWYSON | SDMMC_CALCR_EN,
> +			     SDMMC_CALCR);
>  }
>  
>  static const struct sdhci_ops sdhci_at91_sama5d2_ops = {
> @@ -345,6 +356,14 @@ static int sdhci_at91_probe(struct platform_device *pdev)
>  
>  	priv->restore_needed = false;
>  
> +	/*
> +	 * if SDCAL pin is wrongly connected, we must enable
> +	 * the analog calibration cell permanently.
> +	 */
> +	priv->cal_always_on =
> +		device_property_read_bool(&pdev->dev,
> +					  "microchip,sdcal-inverted");
> +
>  	ret = mmc_of_parse(host->mmc);
>  	if (ret)
>  		goto clocks_disable_unprepare;
> -- 
> 2.17.1
>