[PATCH v4 08/15] can: grcan: optimize DMA by 32-bit accesses

Arun Muthusamy
2026-01-28T14:49:32Z

From: Daniel Hellstrom <daniel@gaisler.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@gaisler.com>
Signed-off-by: Arun Muthusamy <arun.muthusamy@gaisler.com>
---
drivers/net/can/grcan.c | 26 ++++++++++----------------
1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index a752aea51d96..29247e9860c9 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -194,9 +194,6 @@ struct grcan_registers {
#define GRCAN_MSG_OFF 0x00000002
#define GRCAN_MSG_PASS 0x00000001

-#define GRCAN_MSG_DATA_SLOT_INDEX(i) (2 + (i) / 4)
-#define GRCAN_MSG_DATA_SHIFT(i) ((3 - (i) % 4) * 8)
-
#define GRCAN_BUFFER_ALIGNMENT 1024
#define GRCAN_DEFAULT_BUFFER_SIZE 1024
#define GRCAN_VALID_TR_SIZE_MASK 0x001fffc0
@@ -1217,7 +1214,7 @@ 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);
@@ -1253,11 +1250,10 @@ 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;
}
@@ -1396,8 +1392,7 @@ 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;

@@ -1450,11 +1445,10 @@ 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)
+ memcpy(&slot[2], cf->data, sizeof(u32));
+ if (dlc > 4)
+ memcpy(&slot[3], cf->data + 4, sizeof(u32));

/* Checking that channel has not been disabled. These cases
* should never happen
--
2.51.0