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Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree

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On Fri, Apr 29, 2016 at 12:43:39PM -0700, Doug Anderson wrote:
> Russell,
> 
> On Fri, Apr 29, 2016 at 11:12 AM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > On Fri, Apr 29, 2016 at 10:32:15AM -0700, Douglas Anderson wrote:
> >> This series picks patches from various different places to produce what
> >> I consider the best solution to getting consistent mmc and mmcblk
> >> ordering.
> >>
> >> Why consistent ordering and why not just use UUIDs?  IMHO consistent
> >> ordering solves a few different problems:
> >
> > NAK.  Really.  Use UUIDs, that's the proper solution here.
> 
> Un-NAK.  UUIDs don't solve point #1.

Re-NAK.  I don't think your point #1 is valid.  See my other reply.

> * Presumably on a PC you've got an extra bit in the middle (like grub
> or something like that) that can help you resolve your UUIDs even if
> you get your kernel from somewhere else.

You are over-estimating what grub does.  Grub doesn't resolve UUIDs at
all.  Grub just passes the kernel arguments in its configuration file
for the entry it is booting to the kernel.  It's a static configuration
found in /boot/grub/grub.conf.

It doesn't probe devices for UUIDs.

> * Presumably in the non-embedded world kernel hackers have a different
> workflow.  They probably don't swap between different devices with
> different configurations on an hourly basis.  They're not in the habit
> of totally reimaging their system periodically.  Etc.  Trying to force
> the workflow of a PC kernel hacker and an embedded kernel hacker to be
> the same doesn't seem like a worthwhile goal.

In _my_ world with the "embedded" devices I have, I mount by UUID on
platforms which have multiple MMC devices to avoid exactly the problem
you're having.  This works fine.

If I were to switch the SD card, and I wanted to avoid changing the
boot loader configuration, I'd use label instead, and I'd label all
the SD card rootfs using the same label so I could just swap the cards.

> * Presumably an embedded kernel hacker running with ATA / SCSI could
> _usually_ assume that "sda" is his/her root filesystem.  It's unlikely
> an embedded system would have more than one "sda" disk builtin and
> it's nearly guaranteed (I think) that a builtin ATA / SCSI controller
> would probe before any USB based devices.

You've got a funny view again.  N2100 has two hard disks.  The clearfog
board from SolidRun has two mini-PCIe slots, each of which can have two
SATA interfaces... If you want to use it as a server-type platform with
lots of disks...

> Sure, if your root
> filesystem is USB based (really?) and you've got additional USB
> storage devices then you're SOL.  Sorry.

One of my Versatile Express platforms boots from USB, and has a MMC
slot...  So this argument does not stack up.

Sorry.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
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[PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree Douglas Anderson <dianders@chromium.org> - 2016-04-29 19:40 +0200
  [PATCH v2 1/4] Documentation: mmc: Document mmc aliases Douglas Anderson <dianders@chromium.org> - 2016-04-29 19:40 +0200
  [PATCH v2 2/4] mmc: read mmc alias from device tree Douglas Anderson <dianders@chromium.org> - 2016-04-29 19:40 +0200
  [PATCH v2 4/4] ARM: dts: rockchip: Add mmc aliases for rk3288 platform Douglas Anderson <dianders@chromium.org> - 2016-04-29 19:40 +0200
  Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Rob Herring <robh+dt@kernel.org> - 2016-04-29 20:20 +0200
    Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-29 21:40 +0200
      Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-29 22:00 +0200
        Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-29 22:10 +0200
  Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-29 20:20 +0200
    Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-29 21:50 +0200
      Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-29 22:00 +0200
        Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-29 22:10 +0200
          Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-29 23:20 +0200
            Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-29 23:40 +0200
              Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-30 00:00 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-30 00:00 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-30 00:20 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-30 00:30 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-30 00:50 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-30 01:10 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Peter Hurley <peter@hurleysoftware.com> - 2016-04-30 02:00 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Peter Hurley <peter@hurleysoftware.com> - 2016-04-30 02:40 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Doug Anderson <dianders@chromium.org> - 2016-04-30 04:30 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-30 10:40 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Rob Herring <robh+dt@kernel.org> - 2016-04-30 15:30 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Javier Martinez Canillas <javier@dowhile0.org> - 2016-04-30 00:50 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-30 12:50 +0200
                Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Trent Piepho <tpiepho@kymetacorp.com> - 2016-05-03 21:30 +0200
            Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-29 23:40 +0200
          Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-04-29 23:20 +0200
    Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Pavel Machek <pavel@ucw.cz> - 2016-05-04 09:20 +0200
      Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering  w/ device tree Rob Herring <robh+dt@kernel.org> - 2016-05-04 14:30 +0200
        Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk  numbering w/ device tree Pavel Machek <pavel@ucw.cz> - 2016-05-04 14:50 +0200

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