[flashrom] Trouble disabling write-protection on Chromebook

[David Hendricks]

On Mon, Dec 16, 2013 at 9:09 PM, <
BM-2cWKH3wgq8zXX9eHfba16oTc8b61ead4Yq at bitmessage.ch> wrote:

> >> As root in
> >> developer mode, the output of flashrom -v is "flashrom v0.9.4  : 4169bc8
> >> ...". The first time I ran flashrom --wp-disable, I got a message saying
> >> the operation FAILED with error=1. At that point I took the board apart
> >> again and cleaned the write-protect screw hole with q-tips dipped in
> >> rubbing alcohol. When I reassembled the Chromebook and tried again with
> >> flashrom -V --wp-disable, the last few lines I receive are:
> >>
> >> w25_set_srp0: old status: 0xb8
> >> w25_set_srp0: new status: 0xb8
> >> w25q_disable_writeprotect(): error=1.
> >> No -i argument is specified, set ignore_fmap.
> >> FAILED
> >> restore_power_management(): Power management enabled
> >>
> >> As you can see, I can't seem to disable write protection on this chip.
> >> I'm
> >> running stock ChromeOS. Any idea what I might be doing wrong? Thanks in
> >> advance.
> >
> >
> > That's weird... Since you have the system taken apart already, can you
> try
> > disconnecting the battery while the machine is unplugged? I'd recommend
> > leaving it disconnected for a minute or so, the idea being to give the
> SPI
> > ROM enough time to fully discharge and reset.
> >
>
> Thanks for responding. I took your advice and disconnected the battery for
> several minutes. After reassembling the board and running flashrom
> --wp-disable again I am receiving the same message (FAILED). flashrom
> --wp-status says:
>
> WP: status: 0x00b8
> WP: status.srp0: 1
> WP: status.srp1: 0
> WP: write protect is enabled.
> WP: write protect range: start=0x00000000, len=0x00200000


Hmmm, that looks correct for normal circumstances (with write-protection
enabled). Flashrom *should* be able to clear bit 7 of SRP0, so the status
should show up be 0x38 after running with --wp-disable.

Can you try running "flashrom -p host --wp-disable -V" and pasting the
output on paste.flashrom.org?

 > If you have a voltmeter handy, you can also try measuring the voltage on

 > the /WP pin (pin 3). More details on pin configuration can be found in
> the
> > datasheet:
> >
> http://www.winbond-usa.com/hq/enu/ProductAndSales/ProductLines/FlashMemory/SerialFlash/W25Q32DW.htm
> >
>
> I don't have voltmeter; I'm sure I could locate one given enough time
> though. Do you have any other suggestions as to steps I might be
> overlooking here? Otherwise, what should I be looking for specifically in
> the Winbond data sheet?
>

Unfortunately I don't have many ideas here... I've only seen this once and
it seemed to be a defective chip since I couldn't change the write-protect
status by removing the chip and using an external programmer. (This was on
a different machine, and not in a retail unit)

The only reason for failure should be if there is anything bridging the gap
between the copper pads around the write-protect screw hole, thereby
connecting /WP on the chip to ground. If you have a magnifying glass, can
you inspect just to make sure there is nothing connecting those pads? I
assume that since you cleaned the area with rubbing alcohol that there is
no residue from the sticker. I'm wondering if there is a tiny bit of copper
(perhaps from a manufacturing defect) bridging the gap. If so, I'll ask one
of our hardware engineers if it's safe to attempt severing it or if they
have any better ideas.

-- 
David Hendricks (dhendrix)
Systems Software Engineer, Google Inc.
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