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

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Message-ID: <20251118092115.3455-7-arun.muthusamy@gaisler.com>
Date: Tue, 18 Nov 2025 10:21:11 +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 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: Arun Muthusamy <arun.muthusamy@...sler.com>
Signed-off-by: Daniel Hellstrom <daniel@...sler.com>
---
 drivers/net/can/grcan.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index b9b0dd7d53f6..e367581faa57 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -1287,7 +1287,7 @@ 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);
@@ -1323,10 +1323,10 @@ 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) {
+				*(u32 *)(cf->data) = slot[2];
+				if (cf->can_dlc > 4)
+					*(u32 *)(cf->data + 4) = slot[3];
 			}

 			stats->rx_bytes += cf->len;
@@ -1466,8 +1466,7 @@ 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;

@@ -1520,10 +1519,10 @@ 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) {
+		slot[2] = *(u32 *)(cf->data); /* data aligned 64-bit */
+		if (dlc > 4)
+			slot[3] = *(u32 *)(cf->data + 4);
 	}

 	/* Checking that channel has not been disabled. These cases
--
2.51.0