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

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

[Richard Leitner]

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@skidata.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.
 
 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 (!oldcard)
 		host->card = card;
 
-- 
2.1.4

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

[Richard Leitner]

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-WcANXNA0UjBBDgjK7y7TUQ@public.gmane.org>
---
 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.
 
 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 (!oldcard)
 		host->card = card;
 
-- 
2.1.4

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

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

[Jaehoon Chung]

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@skidata.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;
>  
> 

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

[Jaehoon Chung]

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-WcANXNA0UjBBDgjK7y7TUQ@public.gmane.org>
> ---
>  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;
>  
> 

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

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

[Richard Leitner]

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@skidata.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.

Nonetheless you're the experts, therefore if you say it shouldn't be in
the kernel/dt I'd be fine with that too. ;-)

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

[Richard Leitner]

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@skidata.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.

Nonetheless you're the experts, therefore if you say it shouldn't be in
the kernel/dt I'd be fine with that too. ;-)

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

[Rob Herring]

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@skidata.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