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esp.c: only call dma_memory_read function if transfer length is non-zero

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In the cases where mixed DMA/non-DMA transfers are used or no data is
available, it is possible for the calculated transfer length to be zero.
Only call the dma_memory_read 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-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250711204636.542964-5-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
This commit is contained in:
Mark Cave-Ayland
2025-07-15 00:25:10 +02:00
committed by Philippe Mathieu-Daudé
parent e70aa5dc29
commit 9d6df740ec
1 changed files with 13 additions and 7 deletions
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hw/scsi/esp.c
+13 -7
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@@ -487,8 +487,10 @@ static void esp_do_dma(ESPState *s)
case STAT_MO:
if (s->dma_memory_read) {
len = MIN(len, fifo8_num_free(&s->cmdfifo));
s->dma_memory_read(s->dma_opaque, buf, len);
esp_set_tc(s, esp_get_tc(s) - len);
if (len) {
s->dma_memory_read(s->dma_opaque, buf, len);
esp_set_tc(s, esp_get_tc(s) - len);
}
} else {
len = esp_fifo_pop_buf(s, buf, fifo8_num_used(&s->fifo));
len = MIN(fifo8_num_free(&s->cmdfifo), len);
@@ -541,9 +543,11 @@ static void esp_do_dma(ESPState *s)
trace_esp_do_dma(cmdlen, len);
if (s->dma_memory_read) {
len = MIN(len, fifo8_num_free(&s->cmdfifo));
s->dma_memory_read(s->dma_opaque, buf, len);
fifo8_push_all(&s->cmdfifo, buf, len);
esp_set_tc(s, esp_get_tc(s) - len);
if (len) {
s->dma_memory_read(s->dma_opaque, buf, len);
fifo8_push_all(&s->cmdfifo, buf, len);
esp_set_tc(s, esp_get_tc(s) - len);
}
} else {
len = esp_fifo_pop_buf(s, buf, fifo8_num_used(&s->fifo));
len = MIN(fifo8_num_free(&s->cmdfifo), len);
@@ -572,8 +576,10 @@ static void esp_do_dma(ESPState *s)
switch (s->rregs[ESP_CMD]) {
case CMD_TI | CMD_DMA:
if (s->dma_memory_read) {
s->dma_memory_read(s->dma_opaque, s->async_buf, len);
esp_set_tc(s, esp_get_tc(s) - len);
if (len) {
s->dma_memory_read(s->dma_opaque, s->async_buf, len);
esp_set_tc(s, esp_get_tc(s) - len);
}
} else {
/* Copy FIFO data to device */
len = MIN(s->async_len, ESP_FIFO_SZ);