[darwin-kernel] IODMACommands, prepare, and writeBytes
[darwin-kernel] IODMACommands, prepare, and writeBytes
- Subject: [darwin-kernel] IODMACommands, prepare, and writeBytes
- From: Alexander von Below <email@hidden>
- Date: Fri, 5 Oct 2007 15:11:07 +0200
Hello List,
I dislike crossposting, like most people, but as ata-scsi-dev seems to
be rather deserted, forgive me if I repost this on darwin-kernel
We are writing a SCSI HBA, which wants to use DMA. However, some
things -- such as inquiries -- are caught in the driver area. This
information is then to be copied from a local buffer to the
IOMemoryDescriptor of the SCSIParallelTaskIdentifier (obtained from
GetDataBuffer) using writeBytes.
So far, so good.
Now, other commands (notably read and write), are to get their data
via DMA, and here is the probelm:
Documentation tells us we can not prepare anything in a gated context.
Other documentation tells us to use a commandGate for synchronization.
This means, we have to prepare outside of the gated context.
If we prepare the memory descriptor, writeBytes reports success, but
no bytes are delivered to a _ user space process _ sending an inquiry
command via the SCSI Task User Client (the kernel is apparently able
to query our drive still)
If we don't prepare the memory, generating segments fails with
0xe00002d8, "not ready".
We would not like having to make a distinction prior to the gated
context, if we are or are not going to use DMA. How can we handle this
issue?
Thanks for any hints and pointers
Alex
P.S. A DTS Incident for this has been filed, 34298181, but I wanted to
see if the all-knowing list has some insight, too
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