linux-kernel - Re: [PATCH 2/3] tty: serial: Fix build on architecture that does not have ioport

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Date:	Fri, 11 Mar 2011 13:54:14 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@...esas.com>
Cc:	gregkh@...e.de, linux-kernel@...r.kernel.org, arnd@...db.de
Subject: Re: [PATCH 2/3] tty: serial: Fix build on architecture that does
 not have ioport

On Fri, 11 Mar 2011 21:58:11 +0900
Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@...esas.com> wrote:

> Some CPU's do not have ioport. Therefore, these do not have inX/outX.

The results of doing that are usually horrible and add a lot of
configuration and ifdefs.

> This adds CONFIG_SERIAL_8250_IOPORT. When this is enable, 8250 driver
> provides ioports access. And this is not enable with the CPU without
> ioports.

NAK this - all the ifdefs make it hard to maintain. If your platform does
not support inb or outb then it is easier and needs no device
modifications if you just have an architecture file which is something
like

u8 inb(....)
{
	WARN_ON(1);
	return 0xFF;
}

etc

You will then get a backtrace if the methods are called rather than
having to hack all the drivers. In addition if your platform ever has a
PCI bridge attached to it you will now be able to replace those methods
and provide PCI I/O space access, as you will need for many PCI devices.
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