The am53c974 has an design issue where a single byte might be
left in the SCSI FIFO after a DMA transfer.
As the handling code is currently untested add a WARN_ON()
statement here.
Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
---
drivers/scsi/am53c974.c | 6 ++++++
drivers/scsi/esp_scsi.c | 29 +++++++++++++++++++++++++++++
drivers/scsi/esp_scsi.h | 1 +
3 files changed, 36 insertions(+)
diff --git a/drivers/scsi/am53c974.c b/drivers/scsi/am53c974.c
index 86c4c42..1c1312f 100644
--- a/drivers/scsi/am53c974.c
+++ b/drivers/scsi/am53c974.c
@@ -197,6 +197,12 @@ static void pci_esp_dma_drain(struct esp *esp)
shost_printk(KERN_INFO, esp->host,
"DMA blast done (%d tries, %d bytes left)\n", lim, resid);
#endif
+ /* BLAST residual handling is currently untested */
+ if (WARN_ON_ONCE(resid == 1)) {
+ struct esp_cmd_entry *ent = esp->active_cmd;
+
+ ent->flags |= ESP_CMD_FLAG_RESIDUAL;
+ }
}
static void pci_esp_dma_invalidate(struct esp *esp)
diff --git a/drivers/scsi/esp_scsi.c b/drivers/scsi/esp_scsi.c
index 2a3277d..07b4d93 100644
--- a/drivers/scsi/esp_scsi.c
+++ b/drivers/scsi/esp_scsi.c
@@ -1334,6 +1334,35 @@ static int esp_data_bytes_sent(struct esp *esp, struct esp_cmd_entry *ent,
bytes_sent = esp->data_dma_len;
bytes_sent -= ecount;
+ /*
+ * The am53c974 has a DMA 'pecularity'. The doc states:
+ * In some odd byte conditions, one residual byte will
+ * be left in the SCSI FIFO, and the FIFO Flags will
+ * never count to '0 '. When this happens, the residual
+ * byte should be retrieved via PIO following completion
+ * of the BLAST operation.
+ */
+ if (fifo_cnt == 1 && ent->flags & ESP_CMD_FLAG_RESIDUAL) {
+ size_t count = 1;
+ size_t offset = bytes_sent;
+ u8 bval = esp_read8(ESP_FDATA);
+
+ if (ent->flags & ESP_CMD_FLAG_AUTOSENSE)
+ ent->sense_ptr[bytes_sent] = bval;
+ else {
+ struct esp_cmd_priv *p = ESP_CMD_PRIV(cmd);
+ u8 *ptr;
+
+ ptr = scsi_kmap_atomic_sg(p->cur_sg, p->u.num_sg,
+ &offset, &count);
+ if (likely(ptr)) {
+ *(ptr + offset) = bval;
+ scsi_kunmap_atomic_sg(ptr);
+ }
+ }
+ bytes_sent += fifo_cnt;
+ ent->flags &= ~ESP_CMD_FLAG_RESIDUAL;
+ }
if (!(ent->flags & ESP_CMD_FLAG_WRITE))
bytes_sent -= fifo_cnt;
diff --git a/drivers/scsi/esp_scsi.h b/drivers/scsi/esp_scsi.h
index 27dcaf8..5fa456c 100644
--- a/drivers/scsi/esp_scsi.h
+++ b/drivers/scsi/esp_scsi.h
@@ -269,6 +269,7 @@ struct esp_cmd_entry {
#define ESP_CMD_FLAG_WRITE 0x01 /* DMA is a write */
#define ESP_CMD_FLAG_ABORT 0x02 /* being aborted */
#define ESP_CMD_FLAG_AUTOSENSE 0x04 /* Doing automatic REQUEST_SENSE */
+#define ESP_CMD_FLAG_RESIDUAL 0x08 /* AM53c974 BLAST residual */
u8 tag[2];
u8 orig_tag[2];
--
1.8.5.2
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