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>

2 files changed, 30 insertions, 17 deletions

diff --git a/drivers/scsi/esp_scsi.c b/drivers/scsi/esp_scsi.c
index 7ebf2c7d17a4..25cc6fa0535c 100644
--- a/drivers/scsi/esp_scsi.c
+++ b/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 @@ build_identify:
         }
 
         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 @@ build_identify:
                         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 @@ build_identify:
                 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 @@ again:
                         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 @@ again:
         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;
diff --git a/drivers/scsi/esp_scsi.h b/drivers/scsi/esp_scsi.h
index 975d2934d42a..27dcaf84e717 100644
--- a/drivers/scsi/esp_scsi.h
+++ b/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 */