On 02/26/2017 12:51 AM, Alexander Aring wrote:
On 02/22/2017 08:20 PM, Alexandre Macabies wrote:
Hello,
This is not a formal patch. I am trying to add timestamping support to
the drivers/net/ieee802154/mrf24j40.c driver. I need more precise
timestamps that the software ones attached to the packets when
entering/leaving the kernel.
As far as I am aware, the MRF24J40 has no registers[1] to retrieve
hardware timestamps. Thus the idea is to use ktime_get() timestamps at
the proper places in the driver -- hence the *pseudo*-hardware.
Sometimes e.g. at86rf230 has interrupts for that.
- for incoming packets, call ktime_get() in the interrupt handler and
store it for later user. Then push it to skb_hwtstamps just before
sending the skb to ieee802154_rx_irqsafe().
- for outgoing packets, call ktime_get() in the "TX complete"
interrupt handler. This interrupt will only be triggered if the packet
is indeed going out the physical radio, which may no always be the
case, eg. if we send raw garbage on the wpan interface. But I guess
this is fine.
I implemented these changes according to [2] and by looking at existing
timestamping code in other (mostly ethernet) drivers.
Does this method make any sense? Could you do a review of my changes?
Would you be interested in up-streaming these changes once reviewed and
cleaned up?
question: does it work for you use case? :-)
I think it's looking small enough to fit make a minimal implementation
for such tx timestamping for all other users which looking for such
feature.
It seems fairly device-specific. I'm not sure what you mean here or how
it would work.
My question would also be:
Do you can move such handling into ieee802154 subsystem?
Add some functions to mac802154/util.c (should be fine at first, maybe
we need another file if we get hardmac support).
Then offer some API that others driver know when calling timestamp
function (in a very abstract way).
For me:
TX start is when you set some bit to transmit finally the frame.
TX end if when you know that the interrupt was a "tx done" irq.
That's what I see you currently have done in the driver and makes sense
to me.
(Adding alan, the maintainer of the driver)
Thanks for the heads-up Alex.
I think as far as making it generic, timestamping is generic at the
skb-level, which is where it makes sense (since this is not something
specific to 802154, but done on other types of network interfaces as well.
Depending on what kind of precision you need, you might need to get the
timestamping into the actual ISR (which is right now given to (spi->isr)).
Alan.
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