[PATCH v3 72/77] ncr5380: Fix pseudo DMA transfers on 53C400

[Finn Thain]

From: Ondrej Zary <linux@xxxxxxxxxxxxxxxxxxxx>

Pseudo-DMA (PDMA) has been broken for ages, resulting in hangs on
53C400-based cards.

According to 53C400 datasheet, PDMA transfer length must be a multiple
of 128. Check if that's true and use PIO if it's not.

This makes PDMA work on 53C400 (Canon FG2-5202).

Signed-off-by: Ondrej Zary <linux@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>

---
 drivers/scsi/g_NCR5380.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux/drivers/scsi/g_NCR5380.c
===================================================================
--- linux.orig/drivers/scsi/g_NCR5380.c	2015-12-22 12:17:15.000000000 +1100
+++ linux/drivers/scsi/g_NCR5380.c	2015-12-22 12:17:27.000000000 +1100
@@ -702,6 +702,10 @@ static int generic_NCR5380_dma_xfer_len(
 	    !(cmd->SCp.this_residual % transfersize))
 		transfersize = 32 * 1024;
 
+	/* 53C400 datasheet: non-modulo-128-byte transfers should use PIO */
+	if (transfersize % 128)
+		transfersize = 0;
+
 	return transfersize;
 }
 


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