Hi Oliver!
I wish sincerely to thank you again for your time and patience.
On Fri, 26 Jun 2015, Oliver Neukum wrote:
Date: Fri, 26 Jun 2015 10:14:02
From: Oliver Neukum <oneukum@xxxxxxxx>
To: Enrico Mioso <mrkiko.rs@xxxxxxxxx>
Cc: linux-usb@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx
Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
On Thu, 2015-06-25 at 17:19 +0200, Enrico Mioso wrote:
Hi Oliver! And thank you again.
I like / recommend the usage of open messaging standards: my preferred XMPP ID
(JID) is: mrkiko@xxxxxx.
On Thu, 25 Jun 2015, Oliver Neukum wrote:
Date: Thu, 25 Jun 2015 15:38:46
From: Oliver Neukum <oneukum@xxxxxxx>
To: Enrico Mioso <mrkiko.rs@xxxxxxxxx>
Cc: linux-usb@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx
Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
On Thu, 2015-06-25 at 13:44 +0200, Enrico Mioso wrote:
On Thu, 25 Jun 2015, Oliver Neukum wrote:
Is there any advantage in keeping this in a single function?
I did this choice in the light of the fact I think the tx_fixup function will
become more complex than it is now, when aggregating frames.
Yes, but that is a reason to split the helpers up not the opposite.
Right - I understood only now your observation.
the only reason to write the manager that way was that it shouldn't become very
complex - it should simply do things to frames, helping out in building valid
NCM packages.
I answer here your other message to make it more convenient to read: my
intention for the tx_fixup function would be to:
- aggregate frames
- send them out when:
- a timer expires
How would you do that in tx_fixup()? If a timer is required then you
need a separate function.
Sure. I meant: I will adapt it in case needed, and expectin the code to become
a little bit more convoluted.
You cannot become any more convoluted even if you try.
OR
- we have enough data in the aggregate, and cannot add more.
Yes.
You need a third case:
- the interface is taken down.
But in general the logic for that is already there. So can you explain
what additional goals you have?
regarding the "timer logic" I saw it in cdc_ncm.c, but I should study it in
more detail to understand it and implement it here where needed in case.
It is involved. Basically a timer for transmission creates locking
issues. cdc-ncm uses an hrtimer which calls a bottom half which
calls xmit with a NULL skb.
/* if there is a remaining skb, it gets priority */
if (skb != NULL) {
swap(skb, ctx->tx_rem_skb);
swap(sign, ctx->tx_rem_sign);
} else {
ready2send = 1;
}
The else branch here is the timer triggering.
The actual transmission is done in usbnet if cdc_ncm_fill_tx_frame()
returns an skb.
I doubt you can can come up with anything more convoluted
but it simplifies locking.
Well, no, but it supposes a matched commit phase. Can you guarantee
that? I was under the oppression that in that phase you want to actually
give a frame over to the hardware.
No. When Italk about committing, I think about "writing things to out skb".
another reason why i found confortable writing the code this way was to
maintain a kind of statefullness in a more "clean" way.
But I understand this is kind of agruable, and I can if needed break it up as
desired.
Regarding the commit phase - I am not sure I understand your comment, sorry
about that.
However, my intention would be to allow the caller to do calls in sequences
like:
- init frame
- ncm update
- ncm update
- ncm update
...
- ncm update
- ncm commit
(to work in "huawei" mode)
OR
- ncm init frame
- ncm commit
- ncm update
- ncm update
- ncm update
- ncm update
- finalize nth
(to work in "cdc_ncm.c"-mode)..
Sounds like a plan.
But to prevent usbnet from submittinx RX'd packets, I should be doing something
nasty here. And unfortunately don't understand why.
// some devices want funky USB-level framing, for
// win32 driver (usually) and/or hardware quirks
if (info->tx_fixup) {
skb = info->tx_fixup (dev, skb, GFP_ATOMIC);
if (!skb) {
/* packet collected; minidriver waiting for more
*/
if (info->flags & FLAG_MULTI_PACKET)
goto not_drop;
So you just return NULL if you are ready to queue more. But you
need the FLAG_MULTI_PACKET flag.
Unfortuantely I might have not explained myself better.
I should thank you for this illumination on the timer part: since I know I'll need this.
But what's stopping me right now is actually the RX, not the TX part.
Sure, the RX function I am using comes from cdc_ncm.c and works fine: unfortunately, usbnet will not call it.
Infact, my dmesg ends up FULL of
"kevent 2 may have been dropped" messages.
And looking around I discovered I end up triggering a memory check in usbnet.c,
at line 475
skb = __netdev_alloc_skb_ip_align(dev->net, size, flags);
if (!skb) { /* triggered */
netif_dbg(dev, rx_err, dev->net, "no rx skb\n");
usbnet_defer_kevent (dev, EVENT_RX_MEMORY);
usb_free_urb (urb);
return -ENOMEM;
}
And genuinely, I can't understand why.
To test what I was doing wrong, I started with the stock huawei_cdc_ncm.c that
works fine.
then I started allocating the temporary NDP in the bind function: and the
problem started triggering, so I can't RX.
Allocating and deallocating the temporary NDP as-neede as happens now, triggers
the problem inevitably after some packets: ping works for a while.
I was investigating on calls to obtain "private memory" as it happens in the
hso.c driver and others, but wanted some feedback.
What happens then is I get a worker thread using all the CPU and ksoftirqs/0
going mad.
Googling around resulted mainly in people complaining about this same problem
with the drivers/net/usb/smsc95xx.c driver, used in the Raspberry PI for the
Ethernet card.
I imagine in my case what's doing wrong could be terrible but I am not abe to
tell right now.
I tried thinking how to avoid allocating the temporary NDP somehow: without a
solution. And nowI would like to understand what's going wrong even for my
personal kwoledge.
Regards
Oliver
Thank you again, and have a good weekend.
Enrico
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