lkml.org 
[lkml]   [2021]   [Jan]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 1/1] can: dev: add software tx timestamps
Date
Call skb_tx_timestamp() within can_put_echo_skb() so that a software
tx timestamp gets attached on the skb.

There two main reasons to include this call in can_put_echo_skb():

* It easily allow to enable the tx timestamp on all devices with
just one small change.

* According to Documentation/networking/timestamping.rst, the tx
timestamps should be generated in the device driver as close as
possible, but always prior to passing the packet to the network
interface. During the call to can_put_echo_skb(), the skb gets
cloned meaning that the driver should not dereference the skb
variable anymore after can_put_echo_skb() returns. This makes
can_put_echo_skb() the very last place we can use the skb without
having to access the echo_skb[] array.

Remarks:

* By default, skb_tx_timestamp() does nothing. It needs to be
activated by passing the SOF_TIMESTAMPING_TX_SOFTWARE flag either
through socket options or control messages.

* The hardware rx timestamp of a local loopback message is the
hardware tx timestamp. This means that there are no needs to
implement SOF_TIMESTAMPING_TX_HARDWARE for CAN sockets.

References:

Support for the error queue in CAN RAW sockets (which is needed for tx
timestamps) was introduced in:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=eb88531bdbfaafb827192d1fc6c5a3fcc4fadd96

Put the call to skb_tx_timestamp() just before adding it to the array:
https://lkml.org/lkml/2021/1/10/54

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
drivers/net/can/dev.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 3486704c8a95..3904e0874543 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -484,6 +484,8 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,

/* save this skb for tx interrupt echo handling */
priv->echo_skb[idx] = skb;
+
+ skb_tx_timestamp(skb);
} else {
/* locking problem with netif_stop_queue() ?? */
netdev_err(dev, "%s: BUG! echo_skb %d is occupied!\n", __func__, idx);
--
2.26.2
\
 
 \ /
  Last update: 2021-01-10 13:46    [W:0.035 / U:2.592 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site