netdev - Re: [PATCH resend] Renesas Ethernet AVB driver

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Date:	Mon, 13 Apr 2015 23:31:08 +0100
From:	Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:	Lino Sanfilippo <LinoSanfilippo@....de>
Cc:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, devicetree@...r.kernel.org,
	galak@...eaurora.org, netdev@...r.kernel.org,
	linux-sh@...r.kernel.org
Subject: Re: [PATCH resend] Renesas Ethernet AVB driver

On Tue, 2015-04-14 at 00:13 +0200, Lino Sanfilippo wrote:
> Hi,
> 
> On 13.04.2015 22:34, Sergei Shtylyov wrote:
> > Hello.
> > 
> > On 04/02/2015 04:56 PM, Ben Hutchings wrote:
> > 
> >> This driver looks somewhat similar to sh-eth, but lacks some of the
> >> recent bug fixes made to that.  At least commit 283e38db65e7 ("sh_eth:
> >> Fix serialisation of interrupt disable with interrupt & NAPI handler")
> >> appears to be applicable, but there are probably others.
> > 
> >     I suspect this issue applies to many drivers...
> >     I couldn't reproduce the bug that patch was fixing, so left this fix out 
> > for the time being. Others cases were fixed (if applicable).
> 
> Maybe its just harder to trigger but it indeed looks similar to what Ben
> has fixed for sh-eth. I wonder if that shutdown flag in the fix is
> really needed though. IMHO it should be save if we simply call
> napi_disable first, then disable irqs on hardware and finally
> synchronize_irq...

In sh_eth: if we call napi_disable() first, EESR_RX_CHECK can still be
set and nothing will clear it.  If only one CPU is online this can hard
hang the system.  Please trust that I did consider and rule out the
simpler approaches first.

I don't have the full documentation for the EtherAVB block, so I don't
know how its programming model differs from the other Ethernet DMA
engines.  It's possible that a simpler approach will work in ravb.

Ben.


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