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

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Message-ID: <c23d6c4edf92d58aec86da811eaa97a5@agner.ch>
Date:   Sun, 17 Mar 2019 16:05:14 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Marek Vasut <marex@...x.de>
Cc:     Måns Rullgård <mans@...sr.com>,
        Tim Harvey <tharvey@...eworks.com>,
        Douglas Anderson <dianders@...omium.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        shawn.lin@...k-chips.com, Adrian Hunter <adrian.hunter@...el.com>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        Brian Norris <computersforpeace@...il.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Jisheng Zhang <jszhang@...vell.com>,
        linux-rockchip@...ts.infradead.org,
        devicetree-spec@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        open list <linux-kernel@...r.kernel.org>,
        vbyravarasu@...dia.com, Lars-Peter Clausen <lars@...afoo.de>,
        jonathanh@...dia.com, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, Pawel Moll <pawel.moll@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        grundler@...omium.org, Kumar Gala <galak@...eaurora.org>,
        lporzio@...ron.com, Rob Herring <robh+dt@...nel.org>,
        chaotian.jing@...iatek.com,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        sudeep.holla@....com, zhonghui.fu@...ux.intel.com,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v2 0/4] Patches to allow consistent mmc / mmcblk numbering
 w/ device tree

On 16.03.2019 16:39, Russell King - ARM Linux admin wrote:
> On Sat, Mar 16, 2019 at 01:33:58PM +0100, Marek Vasut wrote:
>> If you have a FS or partition table there, it does.
>> If you don't, I agree ... that's a problem.
> 
> eMMC boot partitions are called mmcblkXbootY, and unless you have more
> than one eMMC device on the system, they can be found either by looking
> for /dev/mmcblk*boot* or by querying udev.  The advantage of using udev
> is you can discover the physical device behind it by looking at DEVPATH,
> ID_PATH, etc, but you may not have that installed on an embedded device.
> 
> However, as I say, just looking for /dev/mmcblk*boot* is sufficient to
> find the eMMC boot partitions where there is just one eMMC device
> present (which seems to be the standard setup.)
> 
>> > I don't care the slightest what the numbering is, as long as it is
>> > stable.  On some hardware, with an unpatched kernel, the mmc device
>> > numbering changes depending on whether or not an SD card is inserted on
>> > boot.  Getting rid of that behaviour is really all I want.
>>
>> Agreed, that would be an improvement.
> 
> The mmc device numbering was tied to the mmc host numbering a while back
> and the order that the hosts are probed should be completely independent
> of whether a card is inserted or not:
> 
>         snprintf(md->disk->disk_name, sizeof(md->disk->disk_name),
>                  "mmcblk%u%s", card->host->index, subname ? subname : "");
> 
>         snprintf(rpmb_name, sizeof(rpmb_name),
>                  "mmcblk%u%s", card->host->index, subname ? subname : "");
> 
> I suspect that Mans is quoting something from the dim and distant past
> to confuse the issue - as shown above, it is now dependent on the host
> numbering order not the order in which cards are inserted.

Commit 9aaf3437aa72 ("mmc: block: Use the mmc host device index as the
mmcblk device index") which came in with v4.6 enables constant mmc block
device numbering. I can confirm that it works nicely, and it improved
the situation a lot.

That being said, we still use a patch downstream which allows
renumbering using an alias. We deal with a bunch of different boards
with different SoC's. I have a couple of SD cards with various rootfs
and use internal eMMC boot quite often as well. Remembering which board
uses which numbering is a pain. Maintaining a patch is just easier...
Furthermore, U-Boot allows reordering and all boards I deal with use mmc
0 for the internal eMMC. The aliases allow consistency.

--
Stefan