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

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Message-ID: <20190316153900.xqi55awrockovmsi@shell.armlinux.org.uk>
Date:   Sat, 16 Mar 2019 15:39:01 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     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>,
        stefan@...er.ch, 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 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.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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