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

[Tom Rini]

On Tue, Oct 13, 2015 at 08:24:08AM -0500, Nishanth Menon wrote:
> On Tue, Oct 13, 2015 at 3:03 AM, Lokesh Vutla  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
> >>
> >> PartStart SectorNum Sectors UUIDType
> >>   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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Re: [U-Boot] [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

[Nishanth Menon]

On Tue, Oct 13, 2015 at 3:03 AM, Lokesh Vutla  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
>>
>> PartStart SectorNum Sectors UUIDType
>>   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=14447142172=1=2
-- 
---
Regards,
Nishanth Menon
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