Re: [Lcd4linux-devel] RE: [lcd4linux] problem with i2c connected LCD display

[paul k. <pau...@xs...>]

Thanks for the answers.

If I understand correctly there is no longer a userspace layer for the 
i2c interface. (or at least not supposed to be)
If I understand the pcf8574 kernel module correctly. Is this no more 
then a wrapper around these i2c_smb functions. So it can't be much 
slower then calling them directly.
The main advantage of this concept it that all (byte) devices have these 
read and write files. So you could use any device available.

So for a start, I give the pcf8574 a try. Shouldn't take to long to test.
Lets see if you are right that it is too slow. ;-)

Paul

Luis.F.Correia wrote:

>Ok, i'll try to give as much info as I can... 
>
>  
>
>>-----Original Message-----
>>From: paul kamphuis [mailto:pau...@xs...] 
>>Sent: Friday, February 11, 2005 10:39 AM
>>To: lcd...@li...
>>Subject: Re: [Lcd4linux-devel] RE: [lcd4linux] problem with 
>>i2c connected LCD display
>>
>>Hi there,
>>
>>Thanks for inviting me in! I already gave the 0.10 source 
>>code a quick 
>>look (just a download from the sources on the website, no CVS 
>>access yet)
>>Compiles nicely for me, so no problem there.
>>
>>I agree with Luis his code, it looks nice and usable. But it doesn't 
>>compile :'(
>>I spend some time looking for a solution on the internet, and it is a 
>>bit of a horror story.
>>    
>>
>
>Calm down :) it is now as bad as that...
>
>  
>
>>First Luis, did you ever get this code working? Right now I assume it 
>>could have worked with a 2.4.x kernel.
>>    
>>
>
>Yes, it was tested with 2.4.26, but I'm using a very non standard thing
>that is, not using external I2C things, but the included linux i2c
>'extensions'.
>
>Then I used the i2c driver for the WRAP platform (which is what I was
>working
>on back then). (http://www.pcengines.ch/wrap.htm)
>
>I did not use any kind of modules at all, I did plain old direct access
>to the chip via the i2c_smbus commands.
>
>  
>
>>The thing is, the kernel team decided that user space (application) 
>>access to /dev/.. should not be done. For that reason most kernel 
>>includes are no longer available. Only exception the i2c includes. 
>><linux/i2c.h> etc, but including them results in compile errors. (As 
>>Michael noted)
>>The reason is an undefined __user__  macro. Which  is part  of the 
>>kernel teams effort to change the user space behaviour (if I 
>>understand 
>>correctly). Only found a single note on how to solve it; add #include 
>><linux/compiler.h>. And yes, it compiles nicely. Unfortunatly 
>>it doesn't 
>>link. The i2c_smbus functions are unresolved. So far I found 
>>no solution 
>>for this :'(
>>    
>>
>
>Yes, that was the issue I was trying to solve when I finally gave up.
>We should not do direct kernel mode calls, but use the userspace layer
>the i2c project provides. I could not make it work with my WRAP device.
>
>  
>
>>So how does the kernel team wants us to access devices? If I 
>>understand 
>>it correctly it is supposed to go through dedicated kernel 
>>modules like 
>>pcf8574 (part of the 2.6 kernel) which are supposed to show up as 
>>devices in /sys (sysfs). I am using the Gentoo 2.6.10-r6 kernel and a
>>
>>  modprobe pcf8574
>>    
>>
>
>That combined with the correct bus driver for your hardware should make
>it work OK.
>
>  
>
>>results in a /sys/bus/i2c/devices/0-0020 device. This contains (among 
>>some other files) a read and write file. Apperently writing 
>>to the write 
>>file should write data to the connected pcf8574. (I haven't 
>>tested it yet)
>>
>>So my question is. Would going for the /sys device be the 
>>right solution 
>>for lcd4linux?
>>    
>>
>
>Well, it 'may' work, but it is probably very slow to access. 
>
>You should use the I2C API to access the device (if there is one)
>
>  
>
>>Paul
>>
>>    
>>
>
>Luis Correia
>
>
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>  
>