netdev - Re: [PATCH net-next v3 2/2] stmmac: Fix kernel crashes for jumbo frames

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Message-ID: <1389741646.2025.218.camel@bwh-desktop.uk.level5networks.com>
Date:	Tue, 14 Jan 2014 23:20:46 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Vince Bridgers <vbridgers2013@...il.com>
CC:	<devicetree@...r.kernel.org>, <netdev@...r.kernel.org>,
	Giuseppe CAVALLARO <peppe.cavallaro@...com>,
	<robh+dt@...nel.org>, <pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, Kumar Gala <galak@...eaurora.org>,
	Dinh Nguyen <dinguyen@...era.com>,
	"Rayagond Kokatanur" <rayagond@...avyalabs.com>
Subject: Re: [PATCH net-next v3 2/2] stmmac: Fix kernel crashes for jumbo
 frames

On Tue, 2014-01-14 at 14:44 -0600, Vince Bridgers wrote:
> On Tue, Jan 14, 2014 at 1:53 PM, Ben Hutchings
[...]
> >>
> >>       /*
> >>        * Currently only the properties needed on SPEAr600
> >> @@ -60,6 +64,7 @@ static int stmmac_probe_config_dt(struct platform_device *pdev,
> >>       if (of_device_is_compatible(np, "st,spear600-gmac") ||
> >>               of_device_is_compatible(np, "snps,dwmac-3.70a") ||
> >>               of_device_is_compatible(np, "snps,dwmac")) {
> >> +             of_property_read_u32(np, "max-frame-size", &plat->maxmtu);
> > [...]
> >
> > Is it the maximum frame size, including Ethernet header?  (And then, is
> > the CRC or any VLAN header included in the frame size?)
> > Or is it the MTU, excluding all of those?
> > You really need to be very clear about what this number represents.
> 
> max-frame-size as read from the device tree is defined in the ePAPR
> v1.1 specification. I originally used a name of "max-mtu", but was
> asked to change that since this attribute was already defined in the
> ePAPR v1.1 specification.
[...]

Oh dear, this specification is just as confused as I am.  The example
value in §6.3.1.4 is 1518, implying that it is really the frame size,
including the Ethernet header, any VLAN tag, and maybe the CRC.  However
the full example in Appendix B1 has 0x5dc (== 1500) implying that it is
the MTU.

I suppose you should follow whatever interpretation is already used by
other drivers. :-/

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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