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

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Message-ID: <20170410151740.tnvfnrp5lzvj5acs@rob-hp-laptop>
Date:   Mon, 10 Apr 2017 10:17:40 -0500
From:   Rob Herring <robh@...nel.org>
To:     Richard Leitner <richard.leitner@...data.com>
Cc:     Jaehoon Chung <jh80.chung@...sung.com>, ulf.hansson@...aro.org,
        mark.rutland@....com, 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

On Wed, Apr 05, 2017 at 08:23:29AM +0200, Richard Leitner wrote:
> On 04/05/2017 06:40 AM, Jaehoon Chung wrote:
> > 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..
> 
> Ok.
> 
> >>  
> >>  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.
> 
> Ok. I can add a check to prevent setting it, if it is set already.
> 
> > i didn't check the mmc-util..
> > If mmc-util provides the changing this, the using mmc-util is better than this.
> 
> mmc-utils is providing a enable/disable hwreset feature. But as this
> setting is required for my hardware to allow rebooting it, I thought it
> would be better if it's in the kernel. So I/the hw doesn't have to
> depend on userspace tools.

Doesn't really seem like something you'd want a user to have to care 
about, so in DT seems fine to me.

Rob