Re: [GIT PULL] ARM: SoC fixes for v5.10, part 3 - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arnd Bergmann <arnd@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Doug Anderson <dianders@chromium.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	SoC Team <soc@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [GIT PULL] ARM: SoC fixes for v5.10, part 3
Date: Mon, 30 Nov 2020 18:05:24 +0000	[thread overview]
Message-ID: <20201130180523.GZ1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAHk-=whtySEgkH+VFy9oW8Q-+iuivGBo0hOUcee3DvrsBAQUrA@mail.gmail.com>

On Mon, Nov 30, 2020 at 09:44:03AM -0800, Linus Torvalds wrote:
> On Mon, Nov 30, 2020 at 9:04 AM Doug Anderson <dianders@chromium.org> wrote:
> >
> > Without static assignment, maybe we could do numbering of MMC devices
> > in some type of a pre-probe routine?  Is that what you're suggesting?
> 
> Yes.
> 
> So basically, the way the async probing works for say SCSI is that we
> have multiple "layers of asynchroniety". We have the usual "init calls
> done asynchronously", but then within the init calls themselves you
> can start sub-scans asynchronously.
> 
> In order to get reliable ordering between multiple controllers, the
> PCI bus is probed in order in pci_init() (or whatever), so each SCSI
> controller gets called in a fixed order.
> 
> That then gets to scsi_scan_host() does that async_schedule() thing to
> actually scan the SCSI buses on that host.

I'm afraid that you don't get stable device numbering on x86. You get
something that _looks_ like stable device numbering, but it really
isn't.

If you think that /dev/sda for example is always the machine's internal
HDD, that is wrong.

I have a HP Pavilion laptop with its internal HDD with a Windows
installation. Because I didn't want to destroy that in any way, I
bought an external USB3 SATA enclosure and SSD, and installed Debian
Stable on there.

When I installed Debian stable, the HDD was /dev/sda and the SSD was
/dev/sdb. When I boot Debian, the SSD is /dev/sda and the internal
HDD is /dev/sdb.

Maybe /dev/sda through /dev/sdd should be reserved for internal
motherboard drives?

-- 
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