Date: Fri, 17 Feb 2006 14:39:42 +0300
To: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] SIIG 8-port serial boards support
Message-ID: <20060217113942.GA30787@pazke>
Mail-Followup-To: Russell King <rmk+lkml@arm.linux.org.uk>,
	linux-kernel@vger.kernel.org
References: <20060124082538.GB4855@pazke> <20060124210140.GB23513@flint.arm.linux.org.uk> <20060202102644.GC5034@flint.arm.linux.org.uk> <20060202132726.GD24903@pazke> <20060202201734.GA17329@flint.arm.linux.org.uk> <20060203091308.GA19805@pazke> <20060203092435.GA30738@flint.arm.linux.org.uk>
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From: Andrey Panin <pazke@donpac.ru>
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On 034, 02 03, 2006 at 09:24:36 +0000, Russell King wrote:
> On Fri, Feb 03, 2006 at 12:13:08PM +0300, Andrey Panin wrote:
> > On 033, 02 02, 2006 at 08:17:35 +0000, Russell King wrote:
> > > As I've said many a time, we need a generic way to set different hand-
> > > shaking modes.  I've suggested using some spare bits in termios in the
> > > past, but nothing ever came of that - folk lose interest at that poin=
t.

No wonder they do. Extra bits are not a problem, but for 8250.c we need some
way to glue subdrivers with serial8250_set_termios(). Callback in uart_port
structure ?

> > IMHO there is no need to userspace visible changes to support RS485 on
> > these cards, because some of them are RS485 only and some have jumpers
> > for individual ports.  There is nothing that userspace can configure.
> > We only need to set two bits in ACR according to card type and jumper
> > settings and UART will drive RS485 transiever transparently.
>=20
> In this particular case you may be right, but I'm looking at the bigger
> picture, where plain 16550's may be used for RS485.

Common way to use plain 16550 for RS485 is to wire transiever to the RTS
and force userspace to use RTS/CTS flow control. I doubt there are many=20
other sane way to do it.

> There are drivers which want to implement their own private ioctl to
> enable RS485 mode.  What I'm saying is that we should have one solution,
> not multiple solutions to this problem. When we have such a solution,
> your RS485 card will be able to fit into that model.

But it will need a way to pass ACR value anyway :)

--=20
Andrey Panin		| Linux and UNIX system administrator
pazke@donpac.ru		| PGP key: wwwkeys.pgp.net

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