From: Brian Norris <briannorris@chromium.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Matthias Kaehlcke <mka@chromium.org>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-wireless <linux-wireless@vger.kernel.org>,
linux-spi <linux-spi@vger.kernel.org>,
netdev <netdev@vger.kernel.org>,
swboyd@chromium.org, Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: [PATCH] dt-bindings: Add bindings for aliases node
Date: Tue, 9 Oct 2018 11:31:42 -0700 [thread overview]
Message-ID: <20181009183141.GA126050@ban.mtv.corp.google.com> (raw)
In-Reply-To: <CAMuHMdWe5JYp5eC2PvuG4xEud908Crhm+BhrtxPJ4Uo1-LCc4g@mail.gmail.com>
On Tue, Oct 09, 2018 at 09:22:07AM +0200, Geert Uytterhoeven wrote:
> Please note these aliases become cumbersome once you start considering
> (dynamic) DT overlays. That's why I made them optional in the sh-sci
> serial driver, cfr. commit 7678f4c20fa7670f ("serial: sh-sci: Add support
> for dynamic instances").
Note that as I understand it, the entire point of documenting this sort
of thing is to help solidify the interface between a DT aware boot
program (e.g., bootloader) and a device tree which is provided
separately, to avoid memorizing node/path hierarchy. It doesn't need to
(and doesn't, as I read it) enforce an OS's device naming policy.
> Relevant parts of the commit description are:
>
> On DT platforms, the sh-sci driver requires the presence of "serialN"
> aliases in DT, from which instance IDs are derived. If a DT alias is
> missing, the drivers fails to probe the corresponding serial port.
>
> This becomes cumbersome when considering DT overlays, as currently
> there is no upstream support for dynamically updating the /aliases node
> in DT.
That part is not a DT spec problem :)
> Furthermore, even in the presence of such support, hardcoded
> instance IDs in independent overlays are prone to conflicts.
>
> Hence add support for dynamic instance IDs, to be used in the absence of
> a DT alias. This makes serial ports behave similar to I2C and SPI
> buses, which already support dynamic instances.
This seems to be a much different sort of problem. People always love
having predictable IDs given by the OS (myself included), but that's
just plain hard to do and impossible in some cases. I don't think that's
what this document is about though.
IOW, this document seems pretty consistent with the above: it doesn't
require the usage of aliases (and it seems silly to have a driver
*require* an alias) -- it just documents how one should name such an
alias if you expect multiple independent software components to
understand it.
> To clarify my point: R-Car M2-W has 4 different types of serial ports, for a
> total of 18 ports, and the two ports on a board labeled 0 and 1 may not
> correspond to the physical first two ports (what's "first" in a collection of
> 4 different types?).
>
> Aliases may be fine for referring to the main serial console (labeled
> port 0 on the device, too), and the primary Ethernet interface (so U-Boot
> knows where to add the "local-mac-address" property), but beyond that,
> I think they should be avoided.
That's fair enough. Just because the solution isn't an all-purpose tool
doesn't mean it shouldn't be documented. The general concept is already
in ePAPR, but it's just not very specific about property names.
> Just my two^H^H^Hfive €c.
Thanks,
Brian
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
next prev parent reply other threads:[~2018-10-09 18:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-25 21:02 [PATCH] dt-bindings: Add bindings for aliases node Matthias Kaehlcke
2018-10-09 1:07 ` Brian Norris
2018-10-09 7:22 ` Geert Uytterhoeven
2018-10-09 18:31 ` Brian Norris [this message]
2018-10-12 0:08 ` Matthias Kaehlcke
2018-10-12 16:31 ` Christian Lamparter
2018-10-15 18:00 ` Rob Herring
2018-10-09 5:57 ` Stephen Boyd
2018-10-11 23:50 ` Matthias Kaehlcke
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