[Linux-parport] parport driver unable to detect hardware EPP

Adam Baker parport at baker-net.org.uk
Mon Mar 23 16:22:14 EDT 2009

On Monday 23 March 2009, Leopold Palomo-Avellaneda wrote:

> Hi,
> probably you are doing the correct. The problem is that the parport driver
> is broken in the Dell boxes. I have not been able to use EPP mode in any of
> the Dell boxes that I have in the lab, and I can say you that we have
> several.

I've seen the same issue here on an non Dell machine (Asus A7V333 

> What to do? i don't know. If you have contact with the dell provider, press
> them to help to the linux kernel gurus to solve it. Also, you can look on
> this mail archive, and look for a mail that someones send me about it. It
> show me a method to solve this issue, but I tested it and it didn't work.
In my case the problem is caused by the code chunk

        /* Check for Intel bug. */
        if (priv->ecr) {
                unsigned char i;
                for (i = 0x00; i < 0x80; i += 0x20) {
                        ECR_WRITE (pb, i);
                        if (clear_epp_timeout (pb)) {
                                /* Phony EPP in ECP. */
                                return 0;

in the file drivers/parport/parport_pc.c. If you comment out that chunk of 
code it is detected correctly.

This code exists to check for a fault in a very old Intel chipset but I 
haven't been able to track down exactly what hardware it affects. Given 
enough users who report that the test is broken on modern hardware it could 
likely be removed but there don't seem to be enough people using EPP mode to 
care any more.

Adam Baker

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