[PATCH] zorro_esp: increase maximum dma length to 65536 bytes

[Kars de Jong <jongk@linux-m68k.org>]

When using this driver on a Blizzard 1260, there were failures whenever
DMA transfers from the SCSI bus to memory of 65535 bytes were followed by a
DMA transfer of 1 byte. This caused the byte at offset 65535 to be
overwritten with 0xff. The Blizzard hardware can't handle single byte DMA
transfers.

Besides this issue, limiting the DMA length to something that is not a
multiple of the page size is very inefficient on most file systems.

It seems this limit was chosen because the DMA transfer counter of the ESP
by default is 16 bits wide, thus limiting the length to 65535 bytes.
However, the value 0 means 65536 bytes, which is handled by the ESP and the
Blizzard just fine. It is also the default maximum used by esp_scsi when
drivers don't provide their own dma_length_limit() function.

Signed-off-by: Kars de Jong <jongk@linux-m68k.org>
---
 drivers/scsi/zorro_esp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/zorro_esp.c b/drivers/scsi/zorro_esp.c
index ca8e3abeb2c7..4448567c495d 100644
--- a/drivers/scsi/zorro_esp.c
+++ b/drivers/scsi/zorro_esp.c
@@ -218,7 +218,7 @@ static int fastlane_esp_irq_pending(struct esp *esp)
 static u32 zorro_esp_dma_length_limit(struct esp *esp, u32 dma_addr,
 					u32 dma_len)
 {
-	return dma_len > 0xFFFF ? 0xFFFF : dma_len;
+	return dma_len > (1U << 16) ? (1U << 16) : dma_len;
 }
 
 static void zorro_esp_reset_dma(struct esp *esp)
-- 
2.17.1