linux-kernel - Re: [PATCH] mmc: core: add mmc-card hardware reset enable support

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Message-id: <ea610a5c-3857-14f8-3039-414bee724223@samsung.com>
Date:   Wed, 05 Apr 2017 13:40:33 +0900
From:   Jaehoon Chung <jh80.chung@...sung.com>
To:     Richard Leitner <richard.leitner@...data.com>,
        ulf.hansson@...aro.org, robh+dt@...nel.org, mark.rutland@....com
Cc:     shawn.lin@...k-chips.com, adrian.hunter@...el.com,
        linus.walleij@...aro.org, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        dev@...l1n.net
Subject: Re: [PATCH] mmc: core: add mmc-card hardware reset enable support

Hi,

On 04/04/2017 11:16 PM, Richard Leitner wrote:
> Some eMMCs disable their hardware reset line (RST_N) by default. To enable
> it the host must set the corresponding bit in ECSD. An example for such
> a device is the Micron MTFCxGACAANA-4M.
> 
> This patch adds a new mmc-card devicetree property to let the host enable
> this feature during card initialization.
> 
> Signed-off-by: Richard Leitner <richard.leitner@...data.com>
> ---
>  Documentation/devicetree/bindings/mmc/mmc-card.txt |  3 +++
>  drivers/mmc/core/mmc.c                             | 21 +++++++++++++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mmc/mmc-card.txt b/Documentation/devicetree/bindings/mmc/mmc-card.txt
> index a70fcd6..8590a40 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc-card.txt
> +++ b/Documentation/devicetree/bindings/mmc/mmc-card.txt
> @@ -12,6 +12,9 @@ Required properties:
>  Optional properties:
>  -broken-hpi : Use this to indicate that the mmc-card has a broken hpi
>                implementation, and that hpi should not be used
> +-enable-hw-reset : some eMMC devices have disabled the hw reset functionality
> +                   (RST_N_FUNCTION) by default. By adding this property the
> +                   host will enable it during initialization.

As i know, RST_N_FUNCTION is controlled bit[1:0]
0x0 : RST_n disabled (by default)
0x1 : permanently enabled
0x2 : permanently disabled

I think that it needs to add the description about these..
>  
>  Example:
>  
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index b502601..518d0e3 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1520,9 +1520,16 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>  	int err;
>  	u32 cid[4];
>  	u32 rocr;
> +	struct device_node *np;
> +	bool enable_rst_n = false;
>  
>  	WARN_ON(!host->claimed);
>  
> +	np = mmc_of_find_child_device(host, 0);
> +	if (np && of_device_is_compatible(np, "mmc-card"))
> +		enable_rst_n = of_property_read_bool(np, "enable-hw-reset");
> +	of_node_put(np);
> +
>  	/* Set correct bus mode for MMC before attempting init */
>  	if (!mmc_host_is_spi(host))
>  		mmc_set_bus_mode(host, MMC_BUSMODE_OPENDRAIN);
> @@ -1810,6 +1817,20 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>  		}
>  	}
>  
> +	/*
> +	 * try to enable RST_N if requested
> +	 * This is needed because some eMMC chips disable this function by
> +	 * default.
> +	 */
> +	if (enable_rst_n) {
> +		err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> +				 EXT_CSD_RST_N_FUNCTION, EXT_CSD_RST_N_ENABLED,
> +				 card->ext_csd.generic_cmd6_time);
> +		if (err && err != -EBADMSG)
> +			pr_warn("%s: Enabling RST_N feature failed\n",
> +				mmc_hostname(card->host));
> +	}

If enabled hw-reset, it doesn't need to re-enable this bit.
i didn't check the mmc-util..
If mmc-util provides the changing this, the using mmc-util is better than this.

Best Regards,
Jaehoon Chung

> +
>  	if (!oldcard)
>  		host->card = card;
>  
>