Re: [PATCH 7/7] can: m_can: workaround for transmit data less than 4 bytes
From: Marc Kleine-Budde <mkl@pengutronix.de>
Date: 2014-11-03 16:48:17
Also in:
linux-arm-kernel, linux-can
On 10/29/2014 11:45 AM, Dong Aisheng wrote:
We meet an IC issue that we have to write the full 8 bytes (whatever value for the second word) in Message RAM to avoid bit error for transmit data less than 4 bytes.
Is this a SoC or a m_can problem? Are all versions of the SoC/m_can affected? Is there a m_can version register somewhere?
quoted hunk ↗ jump to hunk
Without the workaround, we can easily see the following errors: root@imx6qdlsolo:~# ip link set can0 up type can bitrate 1000000 [ 66.882520] IPv6: ADDRCONF(NETDEV_CHANGE): can0: link becomes ready root@imx6qdlsolo:~# cansend can0 123#112233 [ 66.935640] m_can 20e8000.can can0: Bit Error Uncorrected Signed-off-by: Dong Aisheng <redacted> --- drivers/net/can/m_can/m_can.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c index 219e0e3..f2d9ebe 100644 --- a/drivers/net/can/m_can/m_can.c +++ b/drivers/net/can/m_can/m_can.c@@ -1058,10 +1058,19 @@ static netdev_tx_t m_can_start_xmit(struct sk_buff *skb, m_can_fifo_write(priv, 0, M_CAN_FIFO_ID, id); m_can_fifo_write(priv, 0, M_CAN_FIFO_DLC, can_len2dlc(cf->len) << 16); - for (i = 0; i < cf->len; i += 4) + for (i = 0; i < cf->len; i += 4) { m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(i / 4), *(u32 *)(cf->data + i)); + /* FIXME: we meet an IC issue that we have to write the full 8
FIXME usually indicates that the driver needs some work here. Just describe your hardware bug, you might add a reference to an errata if available, though.
+ * bytes (whatever value for the second word) in Message RAM to + * avoid bit error for transmit data less than 4 bytes + */ + if (cf->len <= 4) + m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(i / 4 + 1), + 0x0);
This workaround doesn't handle the dlc == 0 case, your error description isn't completely if this is a problem, too. It should be possible to change the for loop to go always to 8, or simply unroll the loop: /* errata description goes here */ m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(0), *(u32 *)(cf->data + 0)); m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(1), *(u32 *)(cf->data + 4));
+ }
+
can_put_echo_skb(skb, dev, 0);
if (priv->can.ctrlmode & CAN_CTRLMODE_FD) {Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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