root@testbat:~# sudo avrdude -p attiny841 -C ~/avrdude_gpio.conf -c RasPi -v

avrdude: Version 6.3-20171130
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2014 Joerg Wunsch

         System wide configuration file is "/root/avrdude_gpio.conf"
         User configuration file is "/root/.avrduderc"
         User configuration file does not exist or is not a regular file, skipping

         Using Port                    : unknown
         Using Programmer              : RasPi
         AVR Part                      : ATtiny841
         Chip Erase delay              : 4500 us
         PAGEL                         : P00
         BS2                           : P00
         RESET disposition             : possible i/o
         RETRY pulse                   : SCK
         serial program mode           : yes
         parallel program mode         : yes
         Timeout                       : 200
         StabDelay                     : 100
         CmdexeDelay                   : 25
         SyncLoops                     : 32
         ByteDelay                     : 0
         PollIndex                     : 3
         PollValue                     : 0x53
         Memory Detail                 :

                                  Block Poll               Page                       Polled
           Memory Type Mode Delay Size  Indx Paged  Size   Size #Pages MinW  MaxW   ReadBack
           ----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
           eeprom        65     6     4    0 no        512    4      0  4000  4500 0xff 0xff
           signature      0     0     0    0 no          3    0      0     0     0 0x00 0x00
           lock           0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           lfuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           hfuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           calibration    0     0     0    0 no          1    0      0     0     0 0x00 0x00
           flash         65     6    16    0 yes      8192   16    512  4500  4500 0xff 0xff
           efuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00

         Programmer Type : linuxgpio
         Description     : Use the Linux sysfs interface to bitbang GPIO lines
         Pin assignment  : /sys/class/gpio/gpio{n}
           RESET   =  12
           SCK     =  24
           MOSI    =  23
           MISO    =  18

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.00s

avrdude: Device signature = 0x1e9315 (probably t841)
avrdude: safemode: lfuse reads as E2
avrdude: safemode: hfuse reads as DD
avrdude: safemode: efuse reads as F5

avrdude: safemode: lfuse reads as E2
avrdude: safemode: hfuse reads as DD
avrdude: safemode: efuse reads as F5
avrdude: safemode: Fuses OK (E:F5, H:DD, L:E2)

avrdude done.  Thank you.