On Mon, 23 Nov 2015, Ondrej Zary wrote:
PDMA seems to be broken in multiple ways. NCR5380_pread cannot process
less than 128 bytes. In fact, 53C400 datasheet says that it's HW
limitation: non-modulo-128-byte transfers should use PIO.
Adding
transfersize = round_down(transfersize, 128);
to generic_NCR5380_dma_xfer_len() improves the situation a bit.
After modprobe, some small reads (8, 4, 24 and 64 bytes) are done using
PIO, then eight 512-byte reads using PDMA and then it fails on a
254-byte read. First 128 bytes are read using PDMA and the next PDMA
operation hangs waiting forever for the host buffer to be ready.
A 128-byte PDMA receive followed by 126-byte PDMA receive? I don't see how
that is possible given round_down(126, 128) == 0. Was this the actual
'len' argument to NCR5380_pread() in g_NCR5380.c?
BTW, I presume that FLAG_NO_DMA_FIXUPS was set (which is the case if you
pass ncr_53c400=1 option with modprobe). Otherwise you could see PDMA IO
sizes like 127 etc.
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