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

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From Doug Anderson <dianders@chromium.org>
Newsgroups linux.kernel
Subject Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering w/ device tree
Date Sat, 30 Apr 2016 04:30:02 +0200
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Hi,

On Fri, Apr 29, 2016 at 5:31 PM, Peter Hurley <peter@hurleysoftware.com> wrote:
> On 04/29/2016 05:03 PM, Doug Anderson wrote:
>> Hi,
>>
>> On Fri, Apr 29, 2016 at 4:58 PM, Peter Hurley <peter@hurleysoftware.com> wrote:
>>
>>     On 04/29/2016 04:01 PM, Doug Anderson wrote:
>>     > * serial allows numbering devices by alias.
>>
>>     Which is in fact a total nightmare.
>>
>>     While stable device order is mandatory in serial because of
>>     console command line parameters and existing userspace expectations,
>>     it is the number one barrier to providing a shared ttyS namespace
>>     for mixed uart platforms.
>>
>>     Stable device order has a very real (and often unforeseen) maintenance
>>     burden.
>>
>>
>> Interesting. I wonder if these burdens are unique to serial or shared
>> by all the other subsystems that allow ordering? Maybe this is all
>> because of legacy reasons?
>
> Well, the specific issue is certainly unique to serial.
> But what I was suggesting is that 5 years from now, these patches
> could be the "legacy reasons" in mmc.
>
> FWIW, there is already a defacto expectation by boot configurations in the
> field that a given mmc block device is stable across boots. The reality
> is that 100000's of kernel command lines look like:
>
>         root=/dev/mmcblk0p2
>
> This was a recent regression fixed by Ulf in commit 9aaf3437aa72
> ("mmc: block: Use the mmc host device index as the mmcblk device index")

Ah.  Well, in this case it sounds like we've already got an
expectation of stable numbering from boot to boot.  I had missed Ulf's
patch, so I guess part 3 of my series isn't actually needed and can be
dropped.

So it's just a question of whether we allow people to manually specify
via device tree.


Note: if we really think using root=/dev/mmcblkNpM is a bad idea then
we should deprecate it and yell about it in the boot log.  Then 5 (or
20) years down the road we could remove the feature when the legacy
burden become a pain.  Note that even if we deprecated
root=/dev/mmcblkNpM I'd still love to see the numbering be consistent
to help folks parse dmesg.


Thanks for your thoughts!


-Doug

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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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