On Tuesday 24 November 2015, Finn Thain wrote: > > 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?
No 126-byte PDMA. The 126 bytes were probably lost (or mixed with the next read?). The next read was also 254 bytes so another 128-byte PDMA transfer. Then modified NCR5380_information_transfer() to transfer the remaining data (126 bytes in this case) using PIO. It did not help, the next PDMA transfer failed too. > 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. Yes, the flag was set. -- Ondrej Zary -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
