can: mcp251x: avoid repeated frame bug

The MCP2515 has a silicon bug causing repeated frame transmission, see section
5 of MCP2515 Rev. B Silicon Errata Revision G (March 2007).

Basically, setting TXBnCTRL.TXREQ in either SPI mode (00 or 11) will eventually
cause the bug. The workaround proposed by Microchip is to use mode 00 and send
a RTS command on the SPI bus to initiate the transmission.

Cc: <stable@vger.kernel.org>
Signed-off-by: Benoît Locher <Benoit.Locher@skf.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/net/can/mcp251x.c b/drivers/net/can/mcp251x.c
index a580db29e50..26e7129332a 100644
--- a/drivers/net/can/mcp251x.c
+++ b/drivers/net/can/mcp251x.c
@@ -83,6 +83,11 @@
 #define INSTRUCTION_LOAD_TXB(n) (0x40 + 2 * (n))
 #define INSTRUCTION_READ_RXB(n) (((n) == 0) ? 0x90 : 0x94)
 #define INSTRUCTION_RESET       0xC0
+#define RTS_TXB0                0x01
+#define RTS_TXB1                0x02
+#define RTS_TXB2                0x04
+#define INSTRUCTION_RTS(n)      (0x80 | ((n) & 0x07))
+
 
 /* MPC251x registers */
 #define CANSTAT       0x0e
@@ -397,6 +402,7 @@ static void mcp251x_hw_tx_frame(struct spi_device *spi, u8 *buf,
 static void mcp251x_hw_tx(struct spi_device *spi, struct can_frame *frame,
                           int tx_buf_idx)
 {
+        struct mcp251x_priv *priv = dev_get_drvdata(&spi->dev);
         u32 sid, eid, exide, rtr;
         u8 buf[SPI_TRANSFER_BUF_LEN];
 
@@ -418,7 +424,10 @@ static void mcp251x_hw_tx(struct spi_device *spi, struct can_frame *frame,
         buf[TXBDLC_OFF] = (rtr << DLC_RTR_SHIFT) | frame->can_dlc;
         memcpy(buf + TXBDAT_OFF, frame->data, frame->can_dlc);
         mcp251x_hw_tx_frame(spi, buf, frame->can_dlc, tx_buf_idx);
-        mcp251x_write_reg(spi, TXBCTRL(tx_buf_idx), TXBCTRL_TXREQ);
+
+        /* use INSTRUCTION_RTS, to avoid "repeated frame problem" */
+        priv->spi_tx_buf[0] = INSTRUCTION_RTS(1 << tx_buf_idx);
+        mcp251x_spi_trans(priv->spi, 1);
 }
 
 static void mcp251x_hw_rx_frame(struct spi_device *spi, u8 *buf,