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

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Message-ID: <4655676A.1000102@gmx.de>
Date:	Thu, 24 May 2007 12:22:34 +0200
From:	"Lars K.W. Gohlke" <lkwg82@....de>
To:	Tilman Schmidt <tilman@...p.cc>
CC:	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	linux-kernel@...r.kernel.org
Subject: Re: How to access correctly serial port inside module?

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Tilman Schmidt schrieb:
> Am 15.05.2007 10:43 schrieb Jan Engelhardt:
>> On May 15 2007 01:00, Tilman Schmidt wrote:
>>> 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.
>> The original poster is quite unclear about how he wants to access the
>> serial port. [...]
>> Unfortunately, my magic sphere is out of order, so I could only take
>> a really really vague guess at what was wanted.
>
> He asked about "the correct way". The document you cited will just
> warn him against one of the many incorrect ones. That's less helpful
> than not answering at all.
>
>>>> 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.
>> This is how 8250.c works.
>
> Exactly. Which is one reason why other parts of the kernel should not
> do it themselves. (Another being of course that if you do it that way,
> your code will only work with that particular type of serial port
> hardware. As the last of the Ten Commandments for C Programmers has
> been declaring for ages, you shouldn't assume that "All the world's a
> VAX^WPC.")
>
> HTH
> T.
>

ok, I have read everything and also have read the chapters about
tty_drivers. However I'm not really understand, how to ... .

I will summarize the concrete scenario, which will lead to the
understanding and further solution of deadling with serial driver.

[scenario]

	1. in userspace I'm doing: > date > /dev/ttyS0
	2. in kernelspace I want to print out this date.

[/scenario]

I'm really new to kernel coding, that's why I maybe understand some
functions not the proper way.

I'm a bit confused.
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