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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e14e82sm14307792f8f.71.2025.07.14.23.20.29 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 14 Jul 2025 23:20:29 -0700 (PDT) From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= To: qemu-devel@nongnu.org Cc: Mark Cave-Ayland , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Paolo Bonzini , Fam Zheng Subject: [PULL 14/17] esp.c: only call dma_memory_read function if transfer length is non-zero Date: Tue, 15 Jul 2025 08:19:14 +0200 Message-ID: <20250715061918.44971-15-philmd@linaro.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250715061918.44971-1-philmd@linaro.org> References: <20250715061918.44971-1-philmd@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::42c; envelope-from=philmd@linaro.org; helo=mail-wr1-x42c.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Mark Cave-Ayland 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 Reviewed-by: Philippe Mathieu-Daudé Tested-by: Philippe Mathieu-Daudé Message-ID: <20250711204636.542964-5-mark.cave-ayland@ilande.co.uk> Signed-off-by: Philippe Mathieu-Daudé --- hw/scsi/esp.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c index 62ba4061492..ec9fcbeddf4 100644 --- a/hw/scsi/esp.c +++ b/hw/scsi/esp.c @@ -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); -- 2.49.0