linux-kernel - Re: [Bug #11382] e1000e: 2.6.27-rc1 corrupts EEPROM/NVM

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Message-ID: <48DBDC92.80605@zytor.com>
Date:	Thu, 25 Sep 2008 11:46:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jiri Kosina <jkosina@...e.cz>
CC:	Frans Pop <elendil@...net.nl>, airlied@...il.com,
	Jeff Garzik <jeff@...zik.org>, davem@...emloft.net,
	Andrew Morton <akpm@...ux-foundation.org>,
	jeffrey.t.kirsher@...el.com, david.vrabel@....com, rjw@...k.pl,
	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	chrisl@...are.com, Ingo Molnar <mingo@...e.hu>,
	jbarnes@...tuousgeek.org, jesse.brandeburg@...il.com
Subject: Re: [Bug #11382] e1000e: 2.6.27-rc1 corrupts EEPROM/NVM

Jiri Kosina wrote:
> 
> Yes, I think that xorg/xorg i915 driver/libdrm/GEM/whatever are the 
> biggest suspect currently, according to the data that has been gathered so 
> far.
> 
> Still, what confuses me a little bit -- the EEPROM of the card is set to 
> all 0xff, once the corruption happens. Isn't that a quite a coincidence, 
> that bytes representing "nothing" in this context are used?
> 

Typical card EEPROMs are serial - either I2C or SPI.  I believe the 
Intel cards use SPI EEPROMs, but I'm not sure.

[Disclaimer: I don't actually know SPI all that well; I know I2C better. 
  However, I'm pretty sure the following argument does apply to both.]

Consider a corruption which turns a read command into a write command -- 
often just a single bit difference.  Now, the EEPROM will expect data in 
to write, but nothing will be driving the data line, so it will 
typically be a 1.  As the host tries to read, it will therefore fill the 
EEPROM with all ones.

	-hpa
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