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SubjectPCI Bus master crashes -- help please
Hi all,

I am currently writing a kernel driver for ver. 2.0.36, but I have some serious
problems with PCI bus master dma mode. The "new" extension card is a HUNT
ENGINEERING HECPCI1 CompactPCI (a motherboard for TI 'C40 DSP modules). It uses
an AMCC S5933 "Matchmaker" PCI chip. In interrupt driven mode, everything works
fine.

Using pci bus master dma mode, in some cases the data transfer simply hangs the
_complete_ kernel, that is: no reaction to keyboard or any other input, no
kernel message at all (e. g. oops, /var/log/messages), ... This behaviour is
highly sensitive to things:

o the S5933 can be configured to request bus mastership only to transfer at
least 4 longwords from memory to the pci device. In this mode, dma works fine,
but if it can request the bus for a single longword, the kernel hangs as
described above.

o In the opposite direction (pci to memory) the S5933 will request bus
mastership for one longword, and the kernel hangs almost at once.

Furthermore, the setting of the PCI_LATENCY_TIMER register seems to influence
how fast the system will crash (although I could not find a setting which does
not produce any crashes).

Could anybody give me a hint what goes wrong? I am almost sure that the
addresses used during dma are correct as the interrupt driven version works
without problems. What about the PCI_LATENCY_TIMER? What value should be used
here? Where to find some more info?

Thanks in advance, Albrecht.

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