On 09/07/2025 12:14, Philippe Mathieu-Daudé wrote:
On 18/6/25 08:12, Mark Cave-Ayland wrote:
In the cases where mixed DMA/non-DMA transfers are used or no data is
available, it is possible to for the calculated transfer length to be
zero. Only call the dma_memory_write function where the transfer length
is non-zero to avoid invoking the DMA engine for a zero length transfer
which can have side-effects (along with generating additional tracing
noise).
Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
---
hw/scsi/esp.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
index ec9fcbeddf..1c7bad8fc0 100644
--- a/hw/scsi/esp.c
+++ b/hw/scsi/esp.c
@@ -631,7 +631,9 @@ static void esp_do_dma(ESPState *s)
switch (s->rregs[ESP_CMD]) {
case CMD_TI | CMD_DMA:
if (s->dma_memory_write) {
- s->dma_memory_write(s->dma_opaque, s->async_buf, len);
+ if (len) {
+ s->dma_memory_write(s->dma_opaque, s->async_buf, len);
+ }
} else {
/* Copy device data to FIFO */
len = MIN(len, fifo8_num_free(&s->fifo));
@@ -681,6 +683,7 @@ static void esp_do_dma(ESPState *s)
As future cleanup, indent could be simplified using 'if (!len) break;'.
I remember when I did the large rewrite of esp.c, I found the logic easier to follow
with the indentation that way. But of course that is something that could always be
revisited later if required.
Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>
buf[0] = s->status;
if (s->dma_memory_write) {
+ /* Length already non-zero */
s->dma_memory_write(s->dma_opaque, buf, len);
} else {
esp_fifo_push_buf(s, buf, len);
@@ -715,6 +718,7 @@ static void esp_do_dma(ESPState *s)
buf[0] = 0;
if (s->dma_memory_write) {
+ /* Length already non-zero */
s->dma_memory_write(s->dma_opaque, buf, len);
} else {
esp_fifo_push_buf(s, buf, len);
ATB,
Mark.
