[PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Heiko Schocher]

On embedded devices, often there is a combination of
removable mmc devices (e.g. MMC/SD cards) and hard
wired ones (e.g. eMMC). Depending on the hardware
configuration, the 'mmcblkN' node might change if
the removable device is available or not at boot time.

E.g. if the removable device is attached at boot time,
it might become mmxblk0. And the hard wired one mmcblk1.
But if the removable device isn't there at boot time,
the hard wired one will become mmcblk0. This makes it
somehow difficult to hard code the root device to the
non-removable device and boot fast.

Signed-off-by: Heiko Schocher <hs@denx.de>
---
Dirk Behme tried to bring this in, last mail I found:
http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/111022.html
where Dirk worked in Arnds suggestion to use the
"/aliases" device node"

I adapt this to the omap_hsmmc driver.

Is there another solution for this problem?
Or why was this patch not accepted to mainline?

 drivers/mmc/card/block.c      | 6 ++++--
 drivers/mmc/host/omap_hsmmc.c | 6 ++++++
 include/linux/mmc/host.h      | 3 +++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index c742cfd..62250d8 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -2106,7 +2106,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
 	struct mmc_blk_data *md;
 	int devidx, ret;
 
-	devidx = find_first_zero_bit(dev_use, max_devices);
+	devidx = find_next_zero_bit(dev_use, max_devices,
+				    card->host->devidx);
 	if (devidx >= max_devices)
 		return ERR_PTR(-ENOSPC);
 	__set_bit(devidx, dev_use);
@@ -2124,7 +2125,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
 	 * index anymore so we keep track of a name index.
 	 */
 	if (!subname) {
-		md->name_idx = find_first_zero_bit(name_use, max_devices);
+		md->name_idx = find_next_zero_bit(name_use, max_devices,
+						  card->host->devidx);
 		__set_bit(md->name_idx, name_use);
 	} else
 		md->name_idx = ((struct mmc_blk_data *)
diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index 7fb0753..0b45b48 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -2059,6 +2059,12 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
 	host->pbias_enabled = 0;
 	host->vqmmc_enabled = 0;
 
+	if (pdev->dev.of_node) {
+		ret = of_alias_get_id(pdev->dev.of_node, "mmcblk");
+		if (ret >= 0)
+			host->mmc->devidx = ret;
+	}
+
 	ret = omap_hsmmc_gpio_init(mmc, host, pdata);
 	if (ret)
 		goto err_gpio;
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 83b81fd..4f071681 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -382,6 +382,9 @@ struct mmc_host {
 	int			dsr_req;	/* DSR value is valid */
 	u32			dsr;	/* optional driver stage (DSR) value */
 
+	/* preferred mmc block device index (mmcblkX) */
+	unsigned int		devidx;
+
 	unsigned long		private[0] ____cacheline_aligned;
 };
 
-- 
2.1.0

Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Lokesh Vutla]

+Nishanth,

On Tuesday 13 October 2015 10:59 AM, Heiko Schocher wrote:
> On embedded devices, often there is a combination of
> removable mmc devices (e.g. MMC/SD cards) and hard
> wired ones (e.g. eMMC). Depending on the hardware
> configuration, the 'mmcblkN' node might change if
> the removable device is available or not at boot time.
> 
> E.g. if the removable device is attached at boot time,
> it might become mmxblk0. And the hard wired one mmcblk1.
> But if the removable device isn't there at boot time,
> the hard wired one will become mmcblk0. This makes it
> somehow difficult to hard code the root device to the
> non-removable device and boot fast.

Why not use "root=PARTUUID=${uuid}" option instead of relying on mmcblk no?
U-Boot can easily detect your partuuid. Refer to [1] on how TI platforms
does this in u-boot.

[1]
http://git.denx.de/?p=u-boot.git;a=commitdiff;h=437bc42e7ff930dc4d4bd47199d2e823cf84bf4c;hp=85d17be374678ec37fd1e55db994a942e400dc80

Thanks and regards,
Lokesh
> 
> Signed-off-by: Heiko Schocher <hs@denx.de>
> ---
> Dirk Behme tried to bring this in, last mail I found:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/111022.html
> where Dirk worked in Arnds suggestion to use the
> "/aliases" device node"
> 
> I adapt this to the omap_hsmmc driver.
> 
> Is there another solution for this problem?
> Or why was this patch not accepted to mainline?
> 
>  drivers/mmc/card/block.c      | 6 ++++--
>  drivers/mmc/host/omap_hsmmc.c | 6 ++++++
>  include/linux/mmc/host.h      | 3 +++
>  3 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index c742cfd..62250d8 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -2106,7 +2106,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>  	struct mmc_blk_data *md;
>  	int devidx, ret;
>  
> -	devidx = find_first_zero_bit(dev_use, max_devices);
> +	devidx = find_next_zero_bit(dev_use, max_devices,
> +				    card->host->devidx);
>  	if (devidx >= max_devices)
>  		return ERR_PTR(-ENOSPC);
>  	__set_bit(devidx, dev_use);
> @@ -2124,7 +2125,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>  	 * index anymore so we keep track of a name index.
>  	 */
>  	if (!subname) {
> -		md->name_idx = find_first_zero_bit(name_use, max_devices);
> +		md->name_idx = find_next_zero_bit(name_use, max_devices,
> +						  card->host->devidx);
>  		__set_bit(md->name_idx, name_use);
>  	} else
>  		md->name_idx = ((struct mmc_blk_data *)
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index 7fb0753..0b45b48 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -2059,6 +2059,12 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  	host->pbias_enabled = 0;
>  	host->vqmmc_enabled = 0;
>  
> +	if (pdev->dev.of_node) {
> +		ret = of_alias_get_id(pdev->dev.of_node, "mmcblk");
> +		if (ret >= 0)
> +			host->mmc->devidx = ret;
> +	}
> +
>  	ret = omap_hsmmc_gpio_init(mmc, host, pdata);
>  	if (ret)
>  		goto err_gpio;
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 83b81fd..4f071681 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -382,6 +382,9 @@ struct mmc_host {
>  	int			dsr_req;	/* DSR value is valid */
>  	u32			dsr;	/* optional driver stage (DSR) value */
>  
> +	/* preferred mmc block device index (mmcblkX) */
> +	unsigned int		devidx;
> +
>  	unsigned long		private[0] ____cacheline_aligned;
>  };
>  
> 

Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Heiko Schocher]

Hello Lokesh,

Am 13.10.2015 um 08:46 schrieb Lokesh Vutla:
> +Nishanth,
>
> On Tuesday 13 October 2015 10:59 AM, Heiko Schocher wrote:
>> On embedded devices, often there is a combination of
>> removable mmc devices (e.g. MMC/SD cards) and hard
>> wired ones (e.g. eMMC). Depending on the hardware
>> configuration, the 'mmcblkN' node might change if
>> the removable device is available or not at boot time.
>>
>> E.g. if the removable device is attached at boot time,
>> it might become mmxblk0. And the hard wired one mmcblk1.
>> But if the removable device isn't there at boot time,
>> the hard wired one will become mmcblk0. This makes it
>> somehow difficult to hard code the root device to the
>> non-removable device and boot fast.
>
> Why not use "root=PARTUUID=${uuid}" option instead of relying on mmcblk no?
> U-Boot can easily detect your partuuid. Refer to [1] on how TI platforms
> does this in u-boot.

Good tip ... I do not know, if it is possible to update U-Boot
on this boards...

Current U-Boot says:
U-Boot 2013.01.01_heads/master-gc7900a0 (2015-05-06 - 20:37:15)

I2C:   ready
DRAM:  512 MiB
[...]
U-Boot# mmc rescan
U-Boot# mmc part

Partition Map for MMC device 0  --   Partition Type: DOS

Part    Start Sector    Num Sectors     UUID            Type
   1     63              144522          000ce343-01     0e Boot
   2     144585          659861          000ce343-02     83
U-Boot# part uuid mmc 0:2 uuid
Unknown command 'part' - try 'help'
U-Boot#

So, if this patch has no chance for mainline, please let me
know it, thanks!

bye,
Heiko
>
> [1]
> http://git.denx.de/?p=u-boot.git;a=commitdiff;h=437bc42e7ff930dc4d4bd47199d2e823cf84bf4c;hp=85d17be374678ec37fd1e55db994a942e400dc80
>
> Thanks and regards,
> Lokesh
>>
>> Signed-off-by: Heiko Schocher <hs@denx.de>
>> ---
>> Dirk Behme tried to bring this in, last mail I found:
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/111022.html
>> where Dirk worked in Arnds suggestion to use the
>> "/aliases" device node"
>>
>> I adapt this to the omap_hsmmc driver.
>>
>> Is there another solution for this problem?
>> Or why was this patch not accepted to mainline?
>>
>>   drivers/mmc/card/block.c      | 6 ++++--
>>   drivers/mmc/host/omap_hsmmc.c | 6 ++++++
>>   include/linux/mmc/host.h      | 3 +++
>>   3 files changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>> index c742cfd..62250d8 100644
>> --- a/drivers/mmc/card/block.c
>> +++ b/drivers/mmc/card/block.c
>> @@ -2106,7 +2106,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>>   	struct mmc_blk_data *md;
>>   	int devidx, ret;
>>
>> -	devidx = find_first_zero_bit(dev_use, max_devices);
>> +	devidx = find_next_zero_bit(dev_use, max_devices,
>> +				    card->host->devidx);
>>   	if (devidx >= max_devices)
>>   		return ERR_PTR(-ENOSPC);
>>   	__set_bit(devidx, dev_use);
>> @@ -2124,7 +2125,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>>   	 * index anymore so we keep track of a name index.
>>   	 */
>>   	if (!subname) {
>> -		md->name_idx = find_first_zero_bit(name_use, max_devices);
>> +		md->name_idx = find_next_zero_bit(name_use, max_devices,
>> +						  card->host->devidx);
>>   		__set_bit(md->name_idx, name_use);
>>   	} else
>>   		md->name_idx = ((struct mmc_blk_data *)
>> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
>> index 7fb0753..0b45b48 100644
>> --- a/drivers/mmc/host/omap_hsmmc.c
>> +++ b/drivers/mmc/host/omap_hsmmc.c
>> @@ -2059,6 +2059,12 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>>   	host->pbias_enabled = 0;
>>   	host->vqmmc_enabled = 0;
>>
>> +	if (pdev->dev.of_node) {
>> +		ret = of_alias_get_id(pdev->dev.of_node, "mmcblk");
>> +		if (ret >= 0)
>> +			host->mmc->devidx = ret;
>> +	}
>> +
>>   	ret = omap_hsmmc_gpio_init(mmc, host, pdata);
>>   	if (ret)
>>   		goto err_gpio;
>> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
>> index 83b81fd..4f071681 100644
>> --- a/include/linux/mmc/host.h
>> +++ b/include/linux/mmc/host.h
>> @@ -382,6 +382,9 @@ struct mmc_host {
>>   	int			dsr_req;	/* DSR value is valid */
>>   	u32			dsr;	/* optional driver stage (DSR) value */
>>
>> +	/* preferred mmc block device index (mmcblkX) */
>> +	unsigned int		devidx;
>> +
>>   	unsigned long		private[0] ____cacheline_aligned;
>>   };
>>
>>
>

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Lokesh Vutla]

On Tuesday 13 October 2015 01:14 PM, Heiko Schocher wrote:
> Hello Lokesh,
> 
> Am 13.10.2015 um 08:46 schrieb Lokesh Vutla:
>> +Nishanth,
>>
>> On Tuesday 13 October 2015 10:59 AM, Heiko Schocher wrote:
>>> On embedded devices, often there is a combination of
>>> removable mmc devices (e.g. MMC/SD cards) and hard
>>> wired ones (e.g. eMMC). Depending on the hardware
>>> configuration, the 'mmcblkN' node might change if
>>> the removable device is available or not at boot time.
>>>
>>> E.g. if the removable device is attached at boot time,
>>> it might become mmxblk0. And the hard wired one mmcblk1.
>>> But if the removable device isn't there at boot time,
>>> the hard wired one will become mmcblk0. This makes it
>>> somehow difficult to hard code the root device to the
>>> non-removable device and boot fast.
>>
>> Why not use "root=PARTUUID=${uuid}" option instead of relying on
>> mmcblk no?
>> U-Boot can easily detect your partuuid. Refer to [1] on how TI platforms
>> does this in u-boot.
> 
> Good tip ... I do not know, if it is possible to update U-Boot
> on this boards...
> 
> Current U-Boot says:
> U-Boot 2013.01.01_heads/master-gc7900a0 (2015-05-06 - 20:37:15)
> 
> I2C:   ready
> DRAM:  512 MiB
> [...]
> U-Boot# mmc rescan
> U-Boot# mmc part
> 
> Partition Map for MMC device 0  --   Partition Type: DOS
> 
> Part    Start Sector    Num Sectors     UUID            Type
>   1     63              144522          000ce343-01     0e Boot
>   2     144585          659861          000ce343-02     83
> U-Boot# part uuid mmc 0:2 uuid
> Unknown command 'part' - try 'help'
> U-Boot#
> 
> So, if this patch has no chance for mainline, please let me
> know it, thanks!
> 

IIRC, Nishanth had posted a patch something similar but got rejected for
some reason. Probably Nishanth can comment more here.

Thanks and regards,
Lokesh

Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Nishanth Menon]

On Tue, Oct 13, 2015 at 3:03 AM, Lokesh Vutla <a0131933@ti.com> wrote:
>
>
> On Tuesday 13 October 2015 01:14 PM, Heiko Schocher wrote:
>> Hello Lokesh,
>>
>> Am 13.10.2015 um 08:46 schrieb Lokesh Vutla:
>>> +Nishanth,
>>>
>>> On Tuesday 13 October 2015 10:59 AM, Heiko Schocher wrote:
>>>> On embedded devices, often there is a combination of
>>>> removable mmc devices (e.g. MMC/SD cards) and hard
>>>> wired ones (e.g. eMMC). Depending on the hardware
>>>> configuration, the 'mmcblkN' node might change if
>>>> the removable device is available or not at boot time.
>>>>
>>>> E.g. if the removable device is attached at boot time,
>>>> it might become mmxblk0. And the hard wired one mmcblk1.
>>>> But if the removable device isn't there at boot time,
>>>> the hard wired one will become mmcblk0. This makes it
>>>> somehow difficult to hard code the root device to the
>>>> non-removable device and boot fast.
>>>
>>> Why not use "root=PARTUUID=${uuid}" option instead of relying on
>>> mmcblk no?
>>> U-Boot can easily detect your partuuid. Refer to [1] on how TI platforms
>>> does this in u-boot.
>>
>> Good tip ... I do not know, if it is possible to update U-Boot
>> on this boards...
>>
>> Current U-Boot says:
>> U-Boot 2013.01.01_heads/master-gc7900a0 (2015-05-06 - 20:37:15)
>>
>> I2C:   ready
>> DRAM:  512 MiB
>> [...]
>> U-Boot# mmc rescan
>> U-Boot# mmc part
>>
>> Partition Map for MMC device 0  --   Partition Type: DOS
>>
>> Part    Start Sector    Num Sectors     UUID            Type
>>   1     63              144522          000ce343-01     0e Boot
>>   2     144585          659861          000ce343-02     83
>> U-Boot# part uuid mmc 0:2 uuid
>> Unknown command 'part' - try 'help'
>> U-Boot#
>>
>> So, if this patch has no chance for mainline, please let me
>> know it, thanks!
>>
>
> IIRC, Nishanth had posted a patch something similar but got rejected for
> some reason. Probably Nishanth can comment more here.
>

overall the feedback I received was for block devices, there is
already an unique method(PARTUUID/uuid) of referencing required device
and mmcxblky aliasing was not really needed - hence dropped my patch
and switched over to partuuid.

CC Tom and u-boot list as well.
for reference the current thread: http://marc.info/?t=144471421700002&r=1&w=2
-- 
---
Regards,
Nishanth Menon

Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Dirk Behme]

On 13.10.2015 07:29, Heiko Schocher wrote:
> On embedded devices, often there is a combination of
> removable mmc devices (e.g. MMC/SD cards) and hard
> wired ones (e.g. eMMC). Depending on the hardware
> configuration, the 'mmcblkN' node might change if
> the removable device is available or not at boot time.
>
> E.g. if the removable device is attached at boot time,
> it might become mmxblk0. And the hard wired one mmcblk1.
> But if the removable device isn't there at boot time,
> the hard wired one will become mmcblk0. This makes it
> somehow difficult to hard code the root device to the
> non-removable device and boot fast.
>
> Signed-off-by: Heiko Schocher <hs@denx.de>
> ---
> Dirk Behme tried to bring this in, last mail I found:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/111022.html
> where Dirk worked in Arnds suggestion to use the
> "/aliases" device node"


The last attempt I remember is from last year


http://www.spinics.net/lists/linux-mmc/msg26586.html

http://www.spinics.net/lists/linux-mmc/msg26588.html


I can't remember why this wasn't accepted, too. But maybe searching 
the archives will help answering that.


Best regards

Dirk


> I adapt this to the omap_hsmmc driver.
>
> Is there another solution for this problem?
> Or why was this patch not accepted to mainline?
>
>   drivers/mmc/card/block.c      | 6 ++++--
>   drivers/mmc/host/omap_hsmmc.c | 6 ++++++
>   include/linux/mmc/host.h      | 3 +++
>   3 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index c742cfd..62250d8 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -2106,7 +2106,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>   	struct mmc_blk_data *md;
>   	int devidx, ret;
>
> -	devidx = find_first_zero_bit(dev_use, max_devices);
> +	devidx = find_next_zero_bit(dev_use, max_devices,
> +				    card->host->devidx);
>   	if (devidx >= max_devices)
>   		return ERR_PTR(-ENOSPC);
>   	__set_bit(devidx, dev_use);
> @@ -2124,7 +2125,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>   	 * index anymore so we keep track of a name index.
>   	 */
>   	if (!subname) {
> -		md->name_idx = find_first_zero_bit(name_use, max_devices);
> +		md->name_idx = find_next_zero_bit(name_use, max_devices,
> +						  card->host->devidx);
>   		__set_bit(md->name_idx, name_use);
>   	} else
>   		md->name_idx = ((struct mmc_blk_data *)
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index 7fb0753..0b45b48 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -2059,6 +2059,12 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>   	host->pbias_enabled = 0;
>   	host->vqmmc_enabled = 0;
>
> +	if (pdev->dev.of_node) {
> +		ret = of_alias_get_id(pdev->dev.of_node, "mmcblk");
> +		if (ret >= 0)
> +			host->mmc->devidx = ret;
> +	}
> +
>   	ret = omap_hsmmc_gpio_init(mmc, host, pdata);
>   	if (ret)
>   		goto err_gpio;
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 83b81fd..4f071681 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -382,6 +382,9 @@ struct mmc_host {
>   	int			dsr_req;	/* DSR value is valid */
>   	u32			dsr;	/* optional driver stage (DSR) value */
>
> +	/* preferred mmc block device index (mmcblkX) */
> +	unsigned int		devidx;
> +
>   	unsigned long		private[0] ____cacheline_aligned;
>   };
>
>

Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Tom Rini]

[-- Attachment #1: Type: text/plain, Size: 2725 bytes --]

On Tue, Oct 13, 2015 at 08:24:08AM -0500, Nishanth Menon wrote:
> On Tue, Oct 13, 2015 at 3:03 AM, Lokesh Vutla <a0131933@ti.com> wrote:
> >
> >
> > On Tuesday 13 October 2015 01:14 PM, Heiko Schocher wrote:
> >> Hello Lokesh,
> >>
> >> Am 13.10.2015 um 08:46 schrieb Lokesh Vutla:
> >>> +Nishanth,
> >>>
> >>> On Tuesday 13 October 2015 10:59 AM, Heiko Schocher wrote:
> >>>> On embedded devices, often there is a combination of
> >>>> removable mmc devices (e.g. MMC/SD cards) and hard
> >>>> wired ones (e.g. eMMC). Depending on the hardware
> >>>> configuration, the 'mmcblkN' node might change if
> >>>> the removable device is available or not at boot time.
> >>>>
> >>>> E.g. if the removable device is attached at boot time,
> >>>> it might become mmxblk0. And the hard wired one mmcblk1.
> >>>> But if the removable device isn't there at boot time,
> >>>> the hard wired one will become mmcblk0. This makes it
> >>>> somehow difficult to hard code the root device to the
> >>>> non-removable device and boot fast.
> >>>
> >>> Why not use "root=PARTUUID=${uuid}" option instead of relying on
> >>> mmcblk no?
> >>> U-Boot can easily detect your partuuid. Refer to [1] on how TI platforms
> >>> does this in u-boot.
> >>
> >> Good tip ... I do not know, if it is possible to update U-Boot
> >> on this boards...
> >>
> >> Current U-Boot says:
> >> U-Boot 2013.01.01_heads/master-gc7900a0 (2015-05-06 - 20:37:15)
> >>
> >> I2C:   ready
> >> DRAM:  512 MiB
> >> [...]
> >> U-Boot# mmc rescan
> >> U-Boot# mmc part
> >>
> >> Partition Map for MMC device 0  --   Partition Type: DOS
> >>
> >> Part    Start Sector    Num Sectors     UUID            Type
> >>   1     63              144522          000ce343-01     0e Boot
> >>   2     144585          659861          000ce343-02     83
> >> U-Boot# part uuid mmc 0:2 uuid
> >> Unknown command 'part' - try 'help'
> >> U-Boot#
> >>
> >> So, if this patch has no chance for mainline, please let me
> >> know it, thanks!
> >>
> >
> > IIRC, Nishanth had posted a patch something similar but got rejected for
> > some reason. Probably Nishanth can comment more here.
> >
> 
> overall the feedback I received was for block devices, there is
> already an unique method(PARTUUID/uuid) of referencing required device
> and mmcxblky aliasing was not really needed - hence dropped my patch
> and switched over to partuuid.

Not telling the kernel what to do here but root=PARTUUID=$x is the long
standing portable multi-architecture (and storage medium) way to have a
stable name for your root device.  The automatic way of digging this
information out in U-Boot is dates back to Sept 2012 in mainline.

-- 
Tom

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