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

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Date:   Sun, 17 Mar 2019 15:43:50 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Marek Vasut <marex@...x.de>, Mark Rutland <mark.rutland@....com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Måns Rullgård <mans@...sr.com>,
        Heiko Stuebner <heiko@...ech.de>,
        devicetree-spec@...r.kernel.org, shawn.lin@...k-chips.com,
        Douglas Anderson <dianders@...omium.org>,
        vbyravarasu@...dia.com, Jisheng Zhang <jszhang@...vell.com>,
        Lars-Peter Clausen <lars@...afoo.de>, jonathanh@...dia.com,
        Jaehoon Chung <jh80.chung@...sung.com>,
        linux-rockchip@...ts.infradead.org, chaotian.jing@...iatek.com,
        devicetree@...r.kernel.org, Pawel Moll <pawel.moll@....com>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        grundler@...omium.org, Tim Harvey <tharvey@...eworks.com>,
        sudeep.holla@....com, lporzio@...ron.com,
        Rob Herring <robh+dt@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Linux MMC List <linux-mmc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Kumar Gala <galak@...eaurora.org>,
        Brian Norris <computersforpeace@...il.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 Sun, Mar 17, 2019 at 04:05:14PM +0100, Stefan Agner wrote:
> 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.

Maybe eMMC should've been given a different block device name?

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