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@xxxxxx> 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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