[flashrom] FAILED: W25Q64.V bios flash on a ThinkPad

[Charlotte Plusplus]

Hello

I am trying to flash a W25Q64.V in a Thinkpad W520 using a Raspberry Pi
To make it easier, I soldered an ISP connector on the motherboard J100
connector (https://www.coreboot.org/Board:lenovo/t520#Flashing) to
make sure I would have a good electrical connection.
WP and HOLD were left floating, and I used the 3.3V from the Raspberry Pi pin 1.
The electrical connection was good: I could read the flash. I did it 4
times to make sure the MD5 matched. They did. The strings inside the
flash matched the bios version, and ifdtool did recognize the image.

When I tried to flash however, something weird happened:

flashrom -w coreboot.pre apt-ge-p linux_spi:dev=/dev/spidev0.0
Calibrating delay loop... delay loop is unreliable, trying to continue OK.
Found Winbond flash chip "W25Q64.V" (8192 kB, SPI) on linux_spi.
Reading old flash chip contents... done.
Erasing and writing flash chip... Erase/write done.
Verifying flash... FAILED at 0x007bbe00! Expected=0x24, Found=0x98,
failed byte count from 0x00000000-0x007fffff: 0x8e4
Your flash chip is in an unknown state.
Please report this on IRC at chat.freenode.net (channel #flashrom) or
mail flashrom at flashrom.org, thanks!

Ever since, I can't access the chip. The laptop can't boot. The
original image can't be restored.

Whenever I try to read the flash using the exact same command line as
before, I get:

flashrom -r w520-bios-backup.bin -V -p linux_spi:dev=/dev/spidev0.0
(...)
Probing for Winbond W25Q64.W, 8192 kB: RDID byte 0 parity violation.
probe_spi_rdid_generic: id1 0x00, id2 0x00
(...)
Found Generic flash chip "unknown SPI chip (RDID)" (0 kB, SPI).

Funny enough, if I don't connect any cable to the raspberry, I get the
exact same error message.

I tried various configuration: with the raspberry pi power, with WP
and HOLD set to high, with external power and WP and HOLD set to high
- nothing works.
I checked the W25Q64 specsheet
(ttps://cdn.sparkfun.com/datasheets/Dev/Teensy/w25q64fv.pdf), the
system board schematics
(http://kythuatphancung.vn/uploads/download/5165b_Wistron_Kendo-3_WS_-_10222-SA_-_ThinkPad_W520.pdf)
but I just don't understand what is happening.

Any suggestion?? I have flashed with this raspberry before, and it
never when bad to the point that I could no longer even read the chip.

I am afraid something really wrong happened. Any help is appreciated.