SCSI Driver Regression and Missing Code Block?

Hi Guys,

I had an interesting experience with my SATA DVD-RW Drives following a Kernel Upgrade from:

2.6.27.19-170.2.35.fc10.i686
to
2.6.28.6 (Vanilla)

I had been previously using a Fedora 10 release, but required the 2.6.28 kernel in order to update the driver for my onboard Intel Graphics chip (apparently some modules required for this process had been moved into the kernel from 27->28). This was required to fix an issue which was preventing correct functionality of a C++ application I'm working on. This C++ application also has a heavy bias on DVD-ROM burning, and this is where my two problems lie.

Rebuilding went smoothly, and the 2.6.28.6 kernel ran as expected in all but 2 areas:
1) When reading from the disc in a DVD-RW Drive, The return values of the IOCTL Call CDROM_DRIVE_STATUS were not the same as the previous kernel values.

2) Maximum burning speed of the drive seems to be very slow; averaging 2.2X instead of the previous 10+X.

I rooted around in the source code to fix issue 1), and found the following code was completely omitted from the function

int sr_drive_status(struct cdrom_device_info *cdi, int slot)

in the file

sr_ioctl.c:

	/* SK/ASC/ASCQ of 2/4/1 means "unit is becoming ready" */
	if (scsi_sense_valid(&sshdr) && sshdr.sense_key == NOT_READY
			&& sshdr.asc == 0x04 && sshdr.ascq == 0x01)
		return CDS_DRIVE_NOT_READY;

My Question is: Is this an intentional change, or an accidental omission? It's pretty weird to have a whole chunk like that missing from a function without a comment. I've had to manually replace this bit of code to regain the functionality I had in the 2.6.27 kernel. This is the only change I had to make, which is even stranger. How come it's different in 2.6.28.6?

Regarding issue 2) - I haven't found a solution to this yet. I've used various tools to check the speed of the drive, and it's set at maximum 16.4X. Using Growisofs to burn the DVDs also displays that the application is attempting to burn at 16.4X, but in reality it only averages 2.2X. This is a major issue for my application, as burn times are absolutely critical.

If I boot my Linux machine using the previous kernel (2.6.27...) I get the maximum burn speeds back. Something has definitely changed in upgrading kernels. I even used the 2.6.27 config file when building the 2.6.28 kernel, so I know all the settings are the same.

Have there been any fundamental changes in the SCSI driver from 2.6.27-19 to 2.6.28.6? how can I get my top burn speeds back?

Thanks in advance for any help or pointers you can give me. I've trawled the net, but the only posts I have found are for IDE drives, and the top solution is to fiddle with uDMA settings - obviously not an option here.

Best regards,

Dominic Driver
Engineer
Paragon Electronic Design Limited
Level 2 21-23 Andrews Avenue
ANZ House
PO Box 30-449, Lower Hutt
New Zealand

Direct: +64 4 5703892
Fax: +64 4 5703 871
mailto:[email protected]
http://www.paragon.co.nz

One of the problems with trying to diagnose the problem is that you're going from a distro kernel to a vanilla kernel. So it's not necessarily something we've taken out -- it could be something they've put in and we don't know about.

So it'd be really nice to see if 2.6.27 vanilla behaves like 2.6.28 vanilla or like 2.6.27-fc. You might also want to try 2.6.29 as Fedora do backport patches from later kernels.

Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."