[PATCH 7/7] can: m_can: workaround for transmit data less than 4 bytes
From: mkl@pengutronix.de (Marc Kleine-Budde)
Date: 2014-11-04 10:33:09
Also in:
linux-can, netdev
On 11/04/2014 10:27 AM, Dong Aisheng wrote:
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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));Yes, i tried to fix it as follows. /* FIXME: 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 */ if (cf->len <= 4) { 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)); } else { for (i = 0; i < cf->len; i += 4) m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(i / 4), *(u32 *)(cf->data + i)); Will update the patch.Both branches of the above if are doing the same thing, I think you can replace the while if ... else ... for with this:Not the same thing. The later one will cover payload up to 64 bytes.
Doh! I'm not used to CAN-FD, yet :) However, I'll apply this fix before adding the CAN-FD support.
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/* 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)); However if writing to DATA(0) and DATA(1) once in the open() function is enough this code should stay as it is.I tried put them into open() function and the quick test showed it worked. Do you think it's ok to put things into open() function for this issue as follows?diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c index 065e4f1..ca55988 100644 --- a/drivers/net/can/m_can/m_can.c +++ b/drivers/net/can/m_can/m_can.c@@ -901,6 +901,15 @@ static void m_can_chip_config(struct net_device *dev) /* set bittiming params */ m_can_set_bittiming(dev); + /* We meet an IC issue that we have to write the full 8
At least on the *insert SoC name here*, an issue with the Message RAM was discovered. Sending CAN frames with dlc less than 4 bytes will lead to bit errors, when the first 8 bytes of the Message RAM have not been initialized (i.e. written to). To work around this issue, the first 8 bytes are initialized here.
+ * bytes (whatever value for the second word) in Message RAM to
+ * avoid bit error for transmit data less than 4 bytes at the first
+ * time. By initializing the first 8 bytes of tx buffer before using
+ * it can avoid such issue.
+ */
+ m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(0), 0x0);
+ m_can_fifo_write(priv, 0, M_CAN_FIFO_DATA(1), 0x0);
+
m_can_config_endisable(priv, false);
}Can you trigger the issue when sending CAN-FD frames with dlc > 8 && dlc < 64? 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 | -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: OpenPGP digital signature URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20141104/f4b29b02/attachment-0001.sig>