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Re: Modified Linux 4.1.20 (mac+scsi) on Quadra 660av

On Mon, 1 Aug 2016, Mac User wrote:

> Hello,
> I'm not able to get the modified Linux 4.1.20 kernel (the one with the 
> SCSI patches) working on a Quadra 660av.  The kernel compiles (in about 
> 18 hours, compared to over 2 weeks on a Mac IIfx), but it panics at boot 
> with ESP SCSI errors (timeouts, resets, no mode sense).  Debian 3.1 
> (with a Linux 2.2.25 kernel) works on the Quadra 660av.  I tried 
> terminating the external SCSI connection; that did not help.

Those patches affect only the mac_scsi driver. That means that they have 
no effect on Quadras (the hardware requires the mac_esp driver).

The two AV models (Quadra 660av and 840av) are the only machines that 
access the ESP chip using PIO. (All of the other Quadras use PDMA.)

What this means is that SCSI transfers on these AV models suffer from 
exactly the same limitation as SCSI transfers on the IIfx: the driver does 
not make use of the DMA hardware. Hence, Mac OS get about ten times better 
disk throughput than Linux on these machines.

Anyway, I have not tested any AV quadra since Linux v3.x. At that time, 
mac_esp worked fine on my 660av.

So I suggest trying an older kernel binary. I can build one for you if you 

BTW, if you were using a cross-compiler (to build a kernel in minutes 
rather than days) you could then use "git bisect" to identify the commit 
that caused the regression, if that's what this is.

> My internal SCSI disk is a Seagate ST318417N with termination, 
> terminator power, and terminator power to bus jumpers set.

ISTR that no SCSI devices should provide terminator power to the bus 
because the Mac does that (except PowerBooks, which do not power the bus).

> I can send pictures of the boot screen, or whatever other output might 
> be helpful.  Or if another kernel is in the works, I can wait and try 
> that.

Please send pictures. You can use the kernel parameter 
"fbcon=font:ProFont6x11" to get more text on the screen if it scrolls too 


> Thanks for any help..
> -Stan

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