Subject: Re: [RFC][PATCH] Way for platforms to alter built-in serial ports
From: David Woodhouse <dwmw2@infradead.org>
To: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       linux-kernel@vger.kernel.org
In-Reply-To: <20041006082919.B18379@flint.arm.linux.org.uk>
References: <200409301014.00725.bjorn.helgaas@hp.com>
	 <20041006082919.B18379@flint.arm.linux.org.uk>
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Date: Mon, 01 Nov 2004 17:15:48 +0000
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On Wed, 2004-10-06 at 08:29 +0100, Russell King wrote:
> The only reason it exists in its current form is because Alan says
> we can't get rid of the serial port initialisation due to the x86
> requirement for serial console to be initialised reasonably early.
> 
> Unfortunately the early console stuff (afaik) never made it in to
> the kernel, so we've had to keep this hanging around.
> 
> Maybe once this problem is solved we can consider dwmw2's suggestion.

Serial console working really early isn't just a requirement for x86.
It's useful elsewhere too. 

The problem is that 'console=ttySx' doesn't actually do anything unless
port numer 'x' is already registered and working. We should fix that --
we ought to be able to use 'console=ttySx' on the command line and have
the console get registered with the core printk code later, when some
8250 sub-driver (8250_platform, 8250_pci, etc.) actually registers the
port which becomes number 'x'. 

That would allow 'early' serial consoles to have none of the horrible
special-cased 'earlyconsole' crap -- we just call register_serial() (or
early_serial_setup() or whatever) as soon as it's actually possible to
poke at the port.

It also fixes the case of serial console on a PCI device.

-- 
dwmw2

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