dbdma: Interpret command lists until STOP - #220
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With dingusdev#214 we started to advertise the IDE DMA support from dingusdev#192 to guests. That appeared to break booting Mac OS 8.x, at least on the Beige G3: the startup disk was not even detected. Mac OS 8.1 sets up an IDE DMA read as INPUT_MORE, then a NOP with its i field set to always, then STOP, which clears the channel's ACTIVE bit. The emulated transfer completion path interpreted only one following descriptor, so it stopped at NOP. NOP raised the interrupt, but STOP was never reached and the channel stayed active. The Mac OS X driver is more tolerant of this, which is why it was not an issue there. The DBDMA Specification, section 1.4, says: "The target fetches command entries and performs the command-entry-specified data-transfer operation, processing command entries until a STOP entry is reached". Keep interpreting ready commands until a transfer blocks or the channel stops, as start() and resume() already did. This is closer to the hardware behavior, and empirically lets Mac OS 8.1 boot again.
b63b658 removed the old ESCC DMA implementation, taking the last users of end_pull_data(), end_push_data(), and get_push_data_remaining() with it. 9fb34ef later removed the last get_pull_data_remaining() call from the sound server. Nothing has called these hooks since. Remove them from DmaOutChannel, DmaInChannel, and DMAChannel instead of carrying dead completion paths alongside the DMA interfaces that are still in use.
mihaip
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With #214 we started to advertise the IDE DMA support from #192 to guests, which appeared to break booting Mac OS 8.x (at least on the Beige G3) - the startup disk was not even detected. It looks like this is because the DMA is enabled, it gets translated to this sequence of descriptors:
1.
INPUT_MORE2.
NOP(with theiinterrupt bit set)3.
STOP(which clears the active bit set)The emulated transfer completion command executed only one following descriptor and stopped at the
NOP. This generated the interrupt and left the channel active, and thus in an inconsistent state. The Mac OS X driver is more tolerant of this, which is why it wasn't an issue there.The DBDMA specification says "The target fetches command entries and performs the command-entry-specified data-transfer operation, processing command entries until a STOP entry is reached", so a loop is more correct (and we were already doing it for
start andresume`, and empirically it allows 8.1 to boot again.As part of fixing this I also noticed that we had some remnants of the old DMA implementation, to remove them.