linux-kernel - [PATCH 3/4] NTB: ntb_transport: Add module parameters use_tx_dma/use_rx

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Message-ID: <20251027004331.562345-4-den@valinux.co.jp>
Date: Mon, 27 Oct 2025 09:43:30 +0900
From: Koichiro Den <den@...inux.co.jp>
To: ntb@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Cc: jdmason@...zu.us,
	dave.jiang@...el.com,
	allenbh@...il.com
Subject: [PATCH 3/4] NTB: ntb_transport: Add module parameters use_tx_dma/use_rx_dma

Allow enabling or disabling DMA separately for TX and RX to optimize
performance depending on the environment. The existing use_dma option is
retained for backward compatibility. Setting it to 1 enables DMA for
both directions.

Signed-off-by: Koichiro Den <den@...inux.co.jp>
---
 drivers/ntb/ntb_transport.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index a447eca27d0f..aee6793812bc 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -92,7 +92,15 @@ MODULE_PARM_DESC(copy_bytes, "Threshold under which NTB will use the CPU to copy
 
 static bool use_dma;
 module_param(use_dma, bool, 0644);
-MODULE_PARM_DESC(use_dma, "Use DMA engine to perform large data copy");
+MODULE_PARM_DESC(use_dma, "Use DMA engine to perform large data copy on both TX and RX");
+
+static bool use_tx_dma;
+module_param(use_tx_dma, bool, 0644);
+MODULE_PARM_DESC(use_tx_dma, "Use DMA engine to perform large data copy on TX");
+
+static bool use_rx_dma;
+module_param(use_rx_dma, bool, 0644);
+MODULE_PARM_DESC(use_rx_dma, "Use DMA engine to perform large data copy on RX");
 
 static bool use_msi;
 #ifdef CONFIG_NTB_MSI
@@ -2047,21 +2055,26 @@ ntb_transport_create_queue(void *data, struct device *client_dev,
 	dma_cap_set(DMA_MEMCPY, dma_mask);
 
 	if (use_dma) {
+		use_tx_dma = true;
+		use_rx_dma = true;
+	}
+	if (use_tx_dma) {
 		qp->tx_dma_chan =
 			dma_request_channel(dma_mask, ntb_dma_filter_fn,
 					    (void *)(unsigned long)node);
 		if (!qp->tx_dma_chan)
 			dev_info(&pdev->dev, "Unable to allocate TX DMA channel\n");
+	} else
+		qp->tx_dma_chan = NULL;
 
+	if (use_rx_dma) {
 		qp->rx_dma_chan =
 			dma_request_channel(dma_mask, ntb_dma_filter_fn,
 					    (void *)(unsigned long)node);
 		if (!qp->rx_dma_chan)
 			dev_info(&pdev->dev, "Unable to allocate RX DMA channel\n");
-	} else {
-		qp->tx_dma_chan = NULL;
+	} else
 		qp->rx_dma_chan = NULL;
-	}
 
 	qp->tx_mw_dma_addr = 0;
 	if (qp->tx_dma_chan) {
-- 
2.48.1