netdev - Re: [PATCH net 2/3] net: cdc_mbim: send ZLP after max sized NTBs

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Message-ID: <87wqv64gr9.fsf@home.kaliuta.org>
Date:	Mon, 21 Jan 2013 18:56:10 +0200
From:	Yauheni Kaliuta <y.kaliuta@...il.com>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Greg Suarez <gsuarez@...thmicro.com>,
	Alexey Orishko <alexey.orishko@...ricsson.com>,
	Oliver Neukum <oneukum@...e.de>
Subject: Re: [PATCH net 2/3] net: cdc_mbim: send ZLP after max sized NTBs


Hi, Bjørn!

>>>>> "BM" == Bjørn Mork writes:

 > We normally avoid sending ZLPs by padding NTBs with a zero byte
 > if the NTB is shorter than dwNtbOutMaxSize, resulting in a short
 > USB packet instead of a ZLP.  But in the case where the NTB length
 > is exactly dwNtbOutMaxSize and this is an exact multiplum of
 > wMaxPacketSize, then we must send a ZLP.

The idea of NCM was to avoid extra ZLPs. If your transfer is exactly
dwNtbOutMaxSize, it's known, you can submit such request on the receiver
side and you do not need any EOT indicatation, so the frametime can be
used for useful data.

I didn't check MBIM specs, but I guess, it wasn't changed. But better get
Alexey's answer for sure.

 > This fixes an issue seen on a Sierra Wireless MC7710 device
 > where the transmission would fail whenever we ended up padding
 > the NTBs to max size.

Is it buggy?

 > Signed-off-by: Bjørn Mork <bjorn@...k.no>
 > ---
 >  drivers/net/usb/cdc_mbim.c |    2 +-
 >  1 file changed, 1 insertion(+), 1 deletion(-)

 > diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c
 > index 42f51c7..3a5673a 100644
 > --- a/drivers/net/usb/cdc_mbim.c
 > +++ b/drivers/net/usb/cdc_mbim.c
 > @@ -366,7 +366,7 @@ err:
 >  
 >  static const struct driver_info cdc_mbim_info = {
 >          .description = "CDC MBIM",
 > -        .flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN,
 > +        .flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN | FLAG_SEND_ZLP,
 >          .bind = cdc_mbim_bind,
 >          .unbind = cdc_mbim_unbind,
 >          .manage_power = cdc_mbim_manage_power,
 > -- 
 > 1.7.10.4



-- 
WBR, Yauheni Kaliuta
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