linux-kernel - [PATCH v2 06/10] can: grcan: optimize DMA by 32-bit accesses

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Message-ID: <20251223105604.12675-7-arun.muthusamy@gaisler.com>
Date: Tue, 23 Dec 2025 11:56:00 +0100
From: Arun Muthusamy <arun.muthusamy@...sler.com>
To: robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
	mkl@...gutronix.de,
	mailhol@...nel.org
Cc: devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-can@...r.kernel.org,
	Daniel Hellstrom <daniel@...sler.com>,
	Arun Muthusamy <arun.muthusamy@...sler.com>
Subject: [PATCH v2 06/10] can: grcan: optimize DMA by 32-bit accesses

From: Daniel Hellstrom <daniel@...sler.com>

Optimizes DMA transfers in the GRCAN driver by reorganizing
data handling to use 32-bit accesses instead of individual
byte accesses.

Signed-off-by: Daniel Hellstrom <daniel@...sler.com>
Signed-off-by: Arun Muthusamy <arun.muthusamy@...sler.com>
---
 drivers/net/can/grcan.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index cac85fbe6acf..8a6c59473cf4 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -1218,7 +1218,7 @@ static int grcan_receive(struct net_device *dev, int budget)
 	struct sk_buff *skb;
 	u32 wr, rd, startrd;
 	u32 *slot;
-	u32 i, rtr, eff, j, shift;
+	u32 rtr, eff;
 	int work_done = 0;
 
 	rd = grcan_read_reg(&regs->rxrd);
@@ -1254,10 +1254,10 @@ static int grcan_receive(struct net_device *dev, int budget)
 		if (rtr) {
 			cf->can_id |= CAN_RTR_FLAG;
 		} else {
-			for (i = 0; i < cf->len; i++) {
-				j = GRCAN_MSG_DATA_SLOT_INDEX(i);
-				shift = GRCAN_MSG_DATA_SHIFT(i);
-				cf->data[i] = (u8)(slot[j] >> shift);
+			if (cf->can_dlc > 0) {
+				memcpy(cf->data, &slot[2], sizeof(u32));
+				if (cf->can_dlc > 4)
+					memcpy(cf->data + 4, &slot[3], sizeof(u32));
 			}
 
 			stats->rx_bytes += cf->len;
@@ -1397,8 +1397,7 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
 	u32 id, txwr, txrd, space, txctrl;
 	int slotindex;
 	u32 *slot;
-	u32 i, rtr, eff, dlc, tmp, err;
-	int j, shift;
+	u32 rtr, eff, dlc, tmp, err;
 	unsigned long flags;
 	u32 oneshotmode = priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT;
 
@@ -1451,10 +1450,11 @@ static netdev_tx_t grcan_start_xmit(struct sk_buff *skb,
 	slot[1] = ((dlc << GRCAN_MSG_DLC_BIT) & GRCAN_MSG_DLC);
 	slot[2] = 0;
 	slot[3] = 0;
-	for (i = 0; i < dlc; i++) {
-		j = GRCAN_MSG_DATA_SLOT_INDEX(i);
-		shift = GRCAN_MSG_DATA_SHIFT(i);
-		slot[j] |= cf->data[i] << shift;
+	if (dlc > 0) {
+		memcpy(&slot[2], cf->data, sizeof(u32));
+		slot[2] = *(u32 *)(cf->data);
+		if (dlc > 4)
+			memcpy(&slot[3], cf->data + 4, sizeof(u32));
 	}
 
 	/* Checking that channel has not been disabled. These cases
-- 
2.51.0