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

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Message-ID: <466885CB.4070702@gmx.de>
Date:	Fri, 08 Jun 2007 00:25:15 +0200
From:	"Lars K.W. Gohlke" <lkwg82@....de>
To:	Tilman Schmidt <tilman@...p.cc>
CC:	huang ying <huang.ying.caritas@...il.com>,
	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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Lars K.W. Gohlke schrieb:
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> Tilman Schmidt schrieb:
>> Am 03.06.2007 22:28 schrieb Lars K.W. Gohlke:
>>> Tilman Schmidt schrieb:
>>>> Am 17.05.2007 08:15 schrieb huang ying:
>>>>> I think the "serio" (through drivers/input/serio/serport.c) may be a
>>>>> choice too, like that in linux/drivers/input/mouse/sermouse.c, which
>>>>> is an example to program serial port in kernel space.
>>>> Interesting. I wonder if that would have been a better choice for
>>>> the Gigaset M101 driver. It seems even to have a probe mechanism
>>>> so one could try to determine if the expected device is really
>>>> connected to the port.
>>>> Is there any documentation on this interface? I find the source a
>>>> bit hard to understand, sparsely commented as it is.
>>> how can I open ttyS1 with major=4 and minor=65?
>>
>> a) With "my" approach, ie. writing a line discipline, you open
>> /dev/ttyS1 in a user space program and then push your line discipline
>> onto it using ioctl(,TIOCSETD,).
>>
>> b) With the "serio" approach, if the probe mechanism is really what
>> I think it is, you register your probe function and wait for it to
>> be called for each active serial port, then do your thing to determine
>> whether this is a/the port you want to use.
>>
>>> Does anybody have some code to read from it the first e.g. 2bytes?
>>
>> That's not how things work in the kernel. You don't "read the first
>> <n> bytes" at will. You have to provide means to process whatever
>> data happens to arrive on the serial port, as it arrives.
>>
>> a) With a line discipline, you provide a callback function
>> ".receive_buf" which will be called by the serial driver if some
>> data has been received, and has to process that data then and there.
>> You might just stow it away in a buffer of course, provided you
>> are sure to get around to processing it later.
>>
>> b) With the "serio" interface, it seems the ".interrupt" function
>> serves the same purpose - though, as I said, I am not really
>> competent on that topic.
>>
>> HTH
>> T.
>>
> ok because I want to handle it in kernel space I will no take option a)
>
> I will try it the way of b)
>
> anyway thx.
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I asked vojtech@...e.cz as one of the driver developer

this is how I did it (just prototype)

(neccessary just one folder and two files)
1. copy template linux-source/drivers/input/joystick/magellan.c
2. insert in line 90  :
	printk("%s:\"%s\"\n",__FUNCTION__, data);
3. make and insert it
4. inputattach --magellan /dev/ttyS0 &
5. date > /dev/ttyS0
6. dmesg | tail

voilà!

[output von dmesg]

	[27336.486980] serio: Serial port ttyS0
	[27336.487270] input: LogiCad3D Magellan / SpaceMouse as
/class/input/input6 [27336.518603] magellan_process_packet:"Mi  6 Jun
19:22:31 CEST 2007"

[/output]
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