am53c974: BLAST residual handling

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.

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>

diff --git a/drivers/scsi/am53c974.c b/drivers/scsi/am53c974.c
index a16c9cf..a42e8db 100644 (file)
--- a/drivers/scsi/am53c974.c
+++ b/drivers/scsi/am53c974.c
@@ -200,6 +200,12 @@ static void pci_esp_dma_drain(struct esp *esp)
        }
        pci_esp_write8(esp, ESP_DMA_CMD_DIR | ESP_DMA_CMD_IDLE, ESP_DMA_CMD);
        esp_dma_log("DMA blast done (%d tries, %d bytes left)\n", lim, resid);
+       /* 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 25cc6fa..4366011 100644 (file)
--- 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 (file)
--- 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];