netdev - RE: [E1000-devel] 82571EB: Detected Hardware Unit Hang

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Message-ID: <1354039840.2701.14.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Tue, 27 Nov 2012 18:10:40 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	"Fujinaka, Todd" <todd.fujinaka@...el.com>,
	Mary Mcgrath <mary.mcgrath@...cle.com>
CC:	Joe Jin <joe.jin@...cle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sf.net" <e1000-devel@...ts.sf.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...r.kernel.org>
Subject: RE: [E1000-devel] 82571EB: Detected Hardware Unit Hang

On Tue, 2012-11-27 at 17:32 +0000, Fujinaka, Todd wrote:
> Forgive me if I'm being too repetitious as I think some of this has
> been mentioned in the past.
> 
> We (and by we I mean the Ethernet part and driver) can only change the
> advertised availability of a larger MaxPayloadSize. The size is
> negotiated by both sides of the link when the link is established. The
> driver should not change the size of the link as it would be poking at
> registers outside of its scope and is controlled by the upstream
> bridge (not us).
[...]

MaxPayloadSize (MPS) is not negotiated between devices but is programmed
by the system firmware (at least for devices present at boot - the
kernel may be responsible in case of hotplug).  You can use the kernel
parameter 'pci=pcie_bus_perf' (or one of several others) to set a policy
that overrides this, but no policy will allow setting MPS above the
device's MaxPayloadSizeSupported (MPSS).

(These parameters are not documented in
Documentation/kernel-parameters.txt!  Someone ought to fix that.)

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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