esp_scsi: use FIFO for command submission

Using DMA for command submission has the drawback that it might
generate additional DMA completion interrupts after the command
has been submitted to the device.
Additionally the am53c974 has a design flaw causing it
to generate spurious interrupts even though DMA completion
interrupts are not enabled.
This can be avoided by using the FIFO for command submission.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/esp_scsi.c

@@ -143,6 +143,24 @@ void scsi_esp_cmd(struct esp *esp, u8 val)
 }
 EXPORT_SYMBOL(scsi_esp_cmd);
 
+static void esp_send_dma_cmd(struct esp *esp, int len, int max_len, int cmd)
+{
+	if (esp->flags & ESP_FLAG_USE_FIFO) {
+		int i;
+
+		scsi_esp_cmd(esp, ESP_CMD_FLUSH);
+		for (i = 0; i < len; i++)
+			esp_write8(esp->command_block[i], ESP_FDATA);
+		scsi_esp_cmd(esp, cmd);
+	} else {
+		if (esp->rev == FASHME)
+			scsi_esp_cmd(esp, ESP_CMD_FLUSH);
+		cmd |= ESP_CMD_DMA;
+		esp->ops->send_dma_cmd(esp, esp->command_block_dma,
+				       len, max_len, 0, cmd);
+	}
+}
+
 static void esp_event(struct esp *esp, u8 val)
 {
 	struct esp_event_ent *p;
@@ -650,10 +668,7 @@ static void esp_autosense(struct esp *esp, struct esp_cmd_entry *ent)
 
 	val = (p - esp->command_block);
 
-	if (esp->rev == FASHME)
-		scsi_esp_cmd(esp, ESP_CMD_FLUSH);
-	esp->ops->send_dma_cmd(esp, esp->command_block_dma,
-			       val, 16, 0, ESP_CMD_DMA | ESP_CMD_SELA);
+	esp_send_dma_cmd(esp, val, 16, ESP_CMD_SELA);
 }
 
 static struct esp_cmd_entry *find_and_prep_issuable_command(struct esp *esp)
@@ -789,12 +804,12 @@ static void esp_maybe_execute_command(struct esp *esp)
 	}
 
 	if (!(esp->flags & ESP_FLAG_DOING_SLOWCMD)) {
-		start_cmd = ESP_CMD_DMA | ESP_CMD_SELA;
+		start_cmd = ESP_CMD_SELA;
 		if (ent->tag[0]) {
 			*p++ = ent->tag[0];
 			*p++ = ent->tag[1];
 
-			start_cmd = ESP_CMD_DMA | ESP_CMD_SA3;
+			start_cmd = ESP_CMD_SA3;
 		}
 
 		for (i = 0; i < cmd->cmd_len; i++)
@@ -814,7 +829,7 @@ static void esp_maybe_execute_command(struct esp *esp)
 			esp->msg_out_len += 2;
 		}
 
-		start_cmd = ESP_CMD_DMA | ESP_CMD_SELAS;
+		start_cmd = ESP_CMD_SELAS;
 		esp->select_state = ESP_SELECT_MSGOUT;
 	}
 	val = tgt;
@@ -834,10 +849,7 @@ static void esp_maybe_execute_command(struct esp *esp)
 		printk("]\n");
 	}
 
-	if (esp->rev == FASHME)
-		scsi_esp_cmd(esp, ESP_CMD_FLUSH);
-	esp->ops->send_dma_cmd(esp, esp->command_block_dma,
-			       val, 16, 0, start_cmd);
+	esp_send_dma_cmd(esp, val, 16, start_cmd);
 }
 
 static struct esp_cmd_entry *esp_get_ent(struct esp *esp)
@@ -1646,7 +1658,7 @@ static int esp_msgin_process(struct esp *esp)
 
 static int esp_process_event(struct esp *esp)
 {
-	int write;
+	int write, i;
 
 again:
 	write = 0;
@@ -1872,6 +1884,10 @@ static int esp_process_event(struct esp *esp)
 			if (esp->msg_out_len == 1) {
 				esp_write8(esp->msg_out[0], ESP_FDATA);
 				scsi_esp_cmd(esp, ESP_CMD_TI);
+			} else if (esp->flags & ESP_FLAG_USE_FIFO) {
+				for (i = 0; i < esp->msg_out_len; i++)
+					esp_write8(esp->msg_out[i], ESP_FDATA);
+				scsi_esp_cmd(esp, ESP_CMD_TI);
 			} else {
 				/* Use DMA. */
 				memcpy(esp->command_block,
@@ -1949,11 +1965,7 @@ static int esp_process_event(struct esp *esp)
 	case ESP_EVENT_CMD_START:
 		memcpy(esp->command_block, esp->cmd_bytes_ptr,
 		       esp->cmd_bytes_left);
-		if (esp->rev == FASHME)
-			scsi_esp_cmd(esp, ESP_CMD_FLUSH);
-		esp->ops->send_dma_cmd(esp, esp->command_block_dma,
-				       esp->cmd_bytes_left, 16, 0,
-				       ESP_CMD_DMA | ESP_CMD_TI);
+		esp_send_dma_cmd(esp, esp->cmd_bytes_left, 16, ESP_CMD_TI);
 		esp_event(esp, ESP_EVENT_CMD_DONE);
 		esp->flags |= ESP_FLAG_QUICKIRQ_CHECK;
 		break;

drivers/scsi/esp_scsi.h

@@ -478,6 +478,7 @@ struct esp {
 #define ESP_FLAG_WIDE_CAPABLE	0x00000008
 #define ESP_FLAG_QUICKIRQ_CHECK	0x00000010
 #define ESP_FLAG_DISABLE_SYNC	0x00000020
+#define ESP_FLAG_USE_FIFO	0x00000040
 
 	u8			select_state;
 #define ESP_SELECT_NONE		0x00 /* Not selecting */