netdev - Re: [PATCH 3/3] net: hisilicon: new hip04 ethernet driver

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Date:	Tue, 25 Mar 2014 18:54:28 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	Zhangfei Gao <zhangfei.gao@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	netdev <netdev@...r.kernel.org>,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 3/3] net: hisilicon: new hip04 ethernet driver

On Tuesday 25 March 2014 10:21:42 Eric Dumazet wrote:
> On Tue, 2014-03-25 at 18:05 +0100, Arnd Bergmann wrote:
> > On Tuesday 25 March 2014 10:00:30 Florian Fainelli wrote:
> >
> > > Using a timer to ensure completion of TX packets is a trick that
> > > worked in the past, but now that the networking stack got smarter,
> > > this might artificially increase the processing time of packets in the
> > > transmit path, and this will defeat features like TCP small queues
> > > etc.. as could be seen with the mvneta driver [1]. The best way really
> > > is to rely on TX completion interrupts when those exist as they cannot
> > > lie about the hardware status (in theory) and they should provide the
> > > fastest way to complete TX packets.
> > 
> > By as Zhangfei Gao pointed out, this hardware does not have a working
> > TX completion interrupt. Using timers to do this has always just been
> > a workaround for broken hardware IMHO.
> 
> For this kind of drivers, calling skb_orphan() from ndo_start_xmit() is
> mandatory.

Cool, thanks for the information, I was wondering already if there was
a way to deal with hardware like this.

	Arnd
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