linux-kernel - Re: [PATCH 0/3] Deterministic UART numbering on Samsung SoCs

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Date:	Thu, 26 Jun 2014 12:39:39 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, Daniel Drake <drake@...lessm.com>,
	Tomasz Figa <tomasz.figa@...il.com>
Subject: Re: [PATCH 0/3] Deterministic UART numbering on Samsung SoCs

On Thu, Jun 26, 2014 at 01:24:32PM +0200, Tomasz Figa wrote:
> Current Samsung UART driver relies on probe order of particular
> samsung-uart instances, which makes it impossible to get proper
> initialization of ports when not all ports are available on board,
> not even saying of deterministic device naming.
> 
> This series intends to fix this situation by adding support to parse
> aliases from device tree and use them to assign instance IDs to
> particular port instances.

How about instead exporting the path/id information so that userspace
can create /dev/serial/by-{path,id}/... for internal devices instead?

The problem you're raising is very much the same problem you have when
there are multiple USB serial devices connected to the machine - you
just get a bunch of /dev/ttyUSB* devices which are unordered (they can
change on each boot, or change order if you disconnect and reconnect
them.)

/dev/serial/by-{path,id}/ allows for a much more stable path.

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