Tuomas,
I think I've tested almost all possible register settings for the chip, but it occurred to me that it is not enough to enable some chip features by flipping bits. The code in esp_scsi would need to be modified to handle the behaviour of these enabled features also.You guessed right about memory failing me - it wasn't about DMA in the end (for some reason, I seem to have DMA stuck in my mind at the moment), Do you see any other avenues to try and enable tagged commands in the ESP chip? We tried one config register only so far...So, rethinking the code in esp_scsi would be one option.
Other versions of ESP SCSI cards do appear to handle TCQ correctly with the default configuration of the chip, i.e. pass on the additional message bytes without any problem. From that I'd guess reading the tag message works OK in the current esp_scsi code. Other features (target mode) we are not really interested in, and without a second initiator on the bus, nothing should ever try to select our ESP host. What else is there to look out for?
The second possibility is that I have a buggy chip in my setup. Removing a sticker from my SCSI-board revealed the chip to be an AMD AM53CF94. There are different versions of the SCSI-boards out there with different chips; NCR, AMD, and QLogic, so if we had more people testing the driver we would find out if the chip is actually the problem. (Is anyone even testing the ISA/PCI cards that use esp_scsi?)
Some Macs/PowerMacs use esp_scsi IIRC - I suspect we would have heard if the driver was broken altogether.
Those are my suggestions at the TCQ problem. But do we really need TCQ?
Maybe not - if no one's missed the feature in the original Amiga ESP drivers, we probably shouldn't worry.
Cheers, Michael