# DVD issues with DMA and udev

## Guinpen

Hello,

I'm having some problems with my DVD writer (IDE PLEXTOR PX-760A), which I can't understand. I'm using the nvidia_pata driver (/dev/sr0), because the old IDE driver (/dev/hda) has problems when writing*. The burner is the only IDE device in the PC.

1) No DMA. The old IDE driver had DMA, but the new one doesn't:

```
hdparm /dev/sr0

/dev/sr0:

 IO_support   =  0 (default 16-bit)

 readonly     =  0 (off)

 readahead    = 256 (on)

 HDIO_GETGEO failed: Inappropriate ioctl for device
```

Is this normal? Reading speed is fine even like that, but writing speed is unacceptable (almost 3 hours to burn a DVD9).

2) Just as I was getting used to no DMA, after a reboot Linux decided once and for all that instead of /dev/cdrom and /dev/dvd and /dev/dvdrw, I were to have /dev/cdrom2, /dev/dvd2 and /dev/dvdrw2... you get the idea. There is no other optical drive in the system, and I don't have /dev/cdrom or /dev/cdrom0 or /dev/cdrom1. WTF? I didn't upgrade udev either, it's version 108.

The problem with /dev/dvd2 etc. is that KDE (or any other software) believes no DVD drive is present unless I point it explicitly to /dev/dvd2, which is annoying or worse.

* After writing a disc with the old IDE driver, the drive would finish writing successfully and then get into an unusable state, continuously spitting nonsense in the syslog. Removing and reinserting modules, or disabling DMA in the BIOS wouldn't help. Only a reboot could fix it.

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## Guinpen

This seems to be an issue with the Plextor drive, rather than motherboard-related. I will try playing with different firmware versions and see what happens.

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## rlittle

Make any headway on this? I have the same plextor unit and the same problem. It burns at 1x no matter what I do.

I haven't tried it with another OS yet.

Edit: almost forget, the dvd3 issue is settings in /etc/udev/rules.d/75-cd-aliases-generator.rules

Mine looks like this:

```
# This file was automatically generated by the /lib/udev/write_cd_rules

# program, probably run by the cd-aliases-generator.rules rules file.

#

# You can modify it, as long as you keep each rule on a single line

# and set the $GENERATED variable.

# DVDR_PX-760A (pci-0000:00:0c.0-scsi-0:0:0:0)

#ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:0c.0-scsi-0:0:0:0", SYMLINK+="dvd3", ENV{GENERATED}="1"

#ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:0c.0-scsi-0:0:0:0", SYMLINK+="cdrw3", ENV{GENERATED}="1"

ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:0c.0-scsi-0:0:0:0", SYMLINK+="dvd", ENV{GENERATED}="1"

ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:0c.0-scsi-0:0:0:0", SYMLINK+="dvdrw", ENV{GENERATED}="1"

# CD-RW_GCE-8526B (pci-0000:00:0c.0-scsi-0:0:1:0)

ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:0c.0-scsi-0:0:1:0", SYMLINK+="cdrom", ENV{GENERATED}="1"

ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:0c.0-scsi-0:0:1:0", SYMLINK+="cdrw", ENV{GENERATED}="1"

```

All you have to is comment out the "cdrom3" and "dvd3" lines in section devoted to your 760A. If you're missing the entries for just "dvd", then just rename "dvd3" to "dvd".

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## Guinpen

Well, it seems that after upgrading kernels (21, but maybe even 20) it works. I'm using the new driver, so it's /dev/sr0 now, and it reads and writes at normal speeds. I also flashed the unit to the latest firmware that was available in September, and that may have played a role too.

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## root_tux_linux

new pata driver use libata

hdX goes srX

srX = scsi

scsi = no DMA and no 32bit I/O

Its normaly...

udev  detect now a new scsi device /dev/srX and will put the old/new device  in /etc/udev/rules.d/70-p*cd

example:

old ide = cdrom

old ide now detect as scsi = cdrom1

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## Guinpen

 *Quote:*   

> srX = scsi 
> 
> scsi = no DMA and no 32bit I/O

 

So, the SCSI subsystem inherently allows fast performance (as fast as with DMA under IDE) without DMA. Is that correct? I don't know much about SCSI.

To rlittle: With the SCSI subsystem on a new kernel >=2.6.21 with the latest firmware for the drive (1.06 if I'm not mistaken) I get normal performance.

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## root_tux_linux

 *Godji wrote:*   

>  *Quote:*   srX = scsi 
> 
> scsi = no DMA and no 32bit I/O 
> 
> So, the SCSI subsystem inherently allows fast performance (as fast as with DMA under IDE) without DMA. Is that correct? I don't know much about SCSI.
> ...

 

yes and you can  remove all Device Driver ----> ATA/ATAPI/MFM/RRL if you dont use any of the old drivers  :Wink: 

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## rlittle

I (due to another surprise that I ran into earlier   :Very Happy:  ) have the new pata drivers and have ditched ATA/ATAPI/MFM/RRL.  And I have /dev/sr0.

Going to check/flash the firmware. Fingers crossed!

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## rlittle

Ha ha! You should see the smile on my face!   :Very Happy:  After one coaster, and a minor panic, it's burning at 4x as I requested on the command line. Thank you root_tux_linux and especially Godji!

Right now I'm running as root with special buffer settings and use-the-force-luke settings for growisofs, but I'll see how little I actually require in the next few days. But those are just details.

Thanks again! That was driving me nuts more than it should have.   :Laughing: 

next step... dual layer DVDs at 8x !!!   :Surprised: 

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