The ESP FIFO is used as a buffer for DMA requests and so isn't guaranteed to
be empty in the case of SCSI errors or a mixed DMA/non-DMA request. Flush the
FIFO before sending a SCSI command to guarantee that it is correctly
positioned at the start of the FIFO.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
 src/hw/esp-scsi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/hw/esp-scsi.c b/src/hw/esp-scsi.c
index cc25f22..e4815aa 100644
--- a/src/hw/esp-scsi.c
+++ b/src/hw/esp-scsi.c
@@ -46,6 +46,7 @@
 #define ESP_DMA_WMAC  0x58c
 
 #define ESP_CMD_DMA      0x80
+#define ESP_CMD_FLUSH    0x01
 #define ESP_CMD_RESET    0x02
 #define ESP_CMD_TI       0x10
 #define ESP_CMD_ICCS     0x11
@@ -96,6 +97,9 @@ esp_scsi_process_op(struct disk_op_s *op)
 
     outb(target, iobase + ESP_WBUSID);
 
+    /* Clear FIFO before sending command.  */
+    outb(ESP_CMD_FLUSH, iobase + ESP_CMD);
+
     /*
      * We need to pass the LUN at the beginning of the command, and the FIFO
      * is only 16 bytes, so we cannot support 16-byte CDBs.  The alternative
-- 
2.39.2

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On 2/8/23 11:48, Mark Cave-Ayland wrote:
> The ESP FIFO is used as a buffer for DMA requests and so isn't guaranteed to
> be empty in the case of SCSI errors or a mixed DMA/non-DMA request. Flush the
> FIFO before sending a SCSI command to guarantee that it is correctly
> positioned at the start of the FIFO.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>   src/hw/esp-scsi.c | 4 ++++
>   1 file changed, 4 insertions(+)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

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