The Xilinx SPI flashing proxies come from here:

https://github.com/quartiq/bscan_spi_bitstreams/blob/single-tap/bscan_spi_xc7a35t.bit?raw=true
https://github.com/quartiq/bscan_spi_bitstreams/blob/single-tap/bscan_spi_xc7a100t.bit?raw=true

These are the "old" single tap versions that are supported by the openocd
release packaged in distros (0.10). If you use the wrong versions you see this:

$ ./openocd/flash-arty microwatt_0.bit
Open On-Chip Debugger 0.10.0
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
none separate
Info : auto-selecting first available session transport "jtag". To override use 'transport select <transport>'.
adapter speed: 25000 kHz
fpga_program
Info : ftdi: if you experience problems at higher adapter clocks, try the command "ftdi_tdo_sample_edge falling"
Info : clock speed 25000 kHz
Info : JTAG tap: xc7.tap tap/device found: 0x0362d093 (mfg: 0x049 (Xilinx), part: 0x362d, ver: 0x0)
loaded file openocd/bscan_spi_xc7a35t.bit to pld device 0 in 0s 152803us
Info : JTAG tap: xc7.tap tap/device found: 0x0362d093 (mfg: 0x049 (Xilinx), part: 0x362d, ver: 0x0)
Error: Unknown flash device (ID 0x00ffffff)

If you find yourself with a later openocd version that contians 867bdb2e9248
("jtagspi: new protocol that includes transfer length"), such as v0.11 as
packaged by Debian Bullseye, you should use the bitstream from the master
branch:

https://github.com/quartiq/bscan_spi_bitstreams/blob/master/bscan_spi_xc7a35t.bit?raw=true
https://github.com/quartiq/bscan_spi_bitstreams/blob/master/bscan_spi_xc7a100t.bit?raw=true

These are in the microwatt repository as bscan_spi_xc7a*t_openocd_v0.11.bit.