linux-kernel - Re: How to access correctly serial port inside module?

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Message-ID: <4648E9F7.5090908@imap.cc>
Date:	Tue, 15 May 2007 01:00:07 +0200
From:	Tilman Schmidt <tilman@...p.cc>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
CC:	"Lars K.W. Gohlke" <lkwg82@....de>, linux-kernel@...r.kernel.org
Subject: Re: How to access correctly serial port inside module?

Am 14.05.2007 22:00 schrieb Jan Engelhardt:
> On May 14 2007 19:40, Lars K.W. Gohlke wrote:
>>>
>>> after searching the mailing list and searching the web, I still don't
>>> know how to access correctly the serial port (in user space known as
>>> /dev/ttyS01)
> 
> http://kernelnewbies.org/FAQ/WhyWritingFilesFromKernelIsBad

That's not nice, sending a newbie on a wild goose chase like that.
He doesn't want to write to a file from kernel after all. Reading
FAQs is never bad, of course, but reading that particular one
won't help him at all with this questions.

Lars: Read that at your leisure if you have time. It is quite
educating, though completely irrelevant to your questions.

>>> would somebody be so kind to give me an example:
>>>
>>> with this behaviour:
>>>
>>> 1. read from port
>>> 2. output via printk()
>>> 3. write to port
> 
> inb/inw/inl, printk, outb/outw/outl.

This is even less nice. You're sending him down the road of
directly programming UART registers, knowing full well (I hope)
that this a Bad Thing. What will you tell him when he comes back
covered in bruises?

Lars: Ignore this advice. You don't want to use in[bwl]/out[bwl]
to directly access serial port hardware for which the kernel has
a working driver already. That way lies pain, as I know from
experience. Read up on the line discipline interface instead, as
described in my previous reply.

HTH
T.

-- 
Tilman Schmidt                          E-Mail: tilman@...p.cc
Bonn, Germany
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