Broken UF2 bootloader in linux mint.

[hetii]

Hello.

After loading uf2 bootloader by: sudo make -C examples/boot-uf2-dfu load new block device is detected but without any partition:

Enumeration logs:

2026-01-08T13:35:40.594065+01:00 nec kernel: usb 5-3.3: new high-speed USB device number 14 using xhci_hcd
2026-01-08T13:35:40.667067+01:00 nec kernel: usb 5-3.3: New USB device found, idVendor=04b4, idProduct=8613, bcdDevice=a0.01
2026-01-08T13:35:40.667075+01:00 nec kernel: usb 5-3.3: New USB device strings: Mfr=0, Product=0, SerialNumber=0
2026-01-08T13:35:40.668064+01:00 nec kernel: usbtest 5-3.3:1.0: FX2 device
2026-01-08T13:35:40.668069+01:00 nec kernel: usbtest 5-3.3:1.0: high-speed {control bulk-in bulk-out} tests (+alt)
2026-01-08T13:35:01.505082+01:00 nec rtkit-daemon[1496]: message repeated 9 times: [ Supervising 2 threads of 2 processes of 1 users.]
2026-01-08T13:35:40.671193+01:00 nec mtp-probe: checking bus 5, device 14: "/sys/devices/pci0000:00/0000:00:08.1/0000:0a:00.3/usb5/5-3/5-3.3"
2026-01-08T13:35:40.671566+01:00 nec mtp-probe: bus: 5, device: 14 was not an MTP device
2026-01-08T13:35:40.685991+01:00 nec mtp-probe: checking bus 5, device 14: "/sys/devices/pci0000:00/0000:00:08.1/0000:0a:00.3/usb5/5-3/5-3.3"
2026-01-08T13:35:40.686087+01:00 nec mtp-probe: bus: 5, device: 14 was not an MTP device


2026-01-08T13:35:55.954995+01:00 nec sudo: pam_ecryptfs: pam_sm_authenticate: /home/dev is already mounted
2026-01-08T13:35:56.289066+01:00 nec kernel: usb 5-3.3: USB disconnect, device number 14
2026-01-08T13:35:56.467065+01:00 nec kernel: usb 5-3.3: new high-speed USB device number 15 using xhci_hcd
2026-01-08T13:35:56.554067+01:00 nec kernel: usb 5-3.3: New USB device found, idVendor=04b4, idProduct=8613, bcdDevice= 0.00
2026-01-08T13:35:56.554076+01:00 nec kernel: usb 5-3.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
2026-01-08T13:35:56.554078+01:00 nec kernel: usb 5-3.3: Product: FX2 series DFU/UF2-class bootloader, UF2 mode
2026-01-08T13:35:56.554078+01:00 nec kernel: usb 5-3.3: Manufacturer: whitequark@whitequark.org
2026-01-08T13:35:56.554079+01:00 nec kernel: usb 5-3.3: SerialNumber: 000000000000
2026-01-08T13:35:56.555060+01:00 nec kernel: usb-storage 5-3.3:1.0: USB Mass Storage device detected
2026-01-08T13:35:56.556059+01:00 nec kernel: scsi host2: usb-storage 5-3.3:1.0
2026-01-08T13:35:56.556063+01:00 nec kernel: usbtest 5-3.3:1.1: FX2 device
2026-01-08T13:35:56.556064+01:00 nec kernel: usbtest 5-3.3:1.1: high-speed {control bulk-in bulk-out} tests (+alt)
2026-01-08T13:35:56.558466+01:00 nec mtp-probe: checking bus 5, device 15: "/sys/devices/pci0000:00/0000:00:08.1/0000:0a:00.3/usb5/5-3/5-3.3"
2026-01-08T13:35:56.558592+01:00 nec mtp-probe: bus: 5, device: 15 was not an MTP device
2026-01-08T13:35:56.577179+01:00 nec mtp-probe: checking bus 5, device 15: "/sys/devices/pci0000:00/0000:00:08.1/0000:0a:00.3/usb5/5-3/5-3.3"
2026-01-08T13:35:56.577320+01:00 nec mtp-probe: bus: 5, device: 15 was not an MTP device
2026-01-08T13:35:57.570064+01:00 nec kernel: scsi 2:0:0:0: Direct-Access     Qi-Hardw Cypress UF2 Boot A0   PQ: 0 ANSI: 0
2026-01-08T13:35:57.571063+01:00 nec kernel: sd 2:0:0:0: Attached scsi generic sg0 type 0
2026-01-08T13:35:57.575063+01:00 nec kernel: sd 2:0:0:0: [sda] 65536 512-byte logical blocks: (33.6 MB/32.0 MiB)
2026-01-08T13:35:57.577058+01:00 nec kernel: sd 2:0:0:0: [sda] Test WP failed, assume Write Enabled
2026-01-08T13:35:57.579063+01:00 nec kernel: sd 2:0:0:0: [sda] Asking for cache data failed
2026-01-08T13:35:57.579068+01:00 nec kernel: sd 2:0:0:0: [sda] Assuming drive cache: write through
2026-01-08T13:35:57.631065+01:00 nec kernel:  sda:
2026-01-08T13:35:57.631071+01:00 nec kernel: sd 2:0:0:0: [sda] Attached SCSI removable disk
2026-01-08T13:35:57.720063+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK cmd_age=0s
2026-01-08T13:35:57.720069+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Sense Key : Hardware Error [current] 
2026-01-08T13:35:57.720070+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Add. Sense: No additional sense information
2026-01-08T13:35:57.720070+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 CDB: Read(10) 28 00 00 00 02 00 00 00 08 00
2026-01-08T13:35:57.720071+01:00 nec kernel: I/O error, dev sda, sector 512 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
2026-01-08T13:35:57.796064+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK cmd_age=0s
2026-01-08T13:35:57.796069+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Sense Key : Hardware Error [current] 
2026-01-08T13:35:57.796069+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Add. Sense: No additional sense information
2026-01-08T13:35:57.796070+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 CDB: Read(10) 28 00 00 00 02 00 00 00 08 00
2026-01-08T13:35:57.796071+01:00 nec kernel: I/O error, dev sda, sector 512 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
2026-01-08T13:35:57.796071+01:00 nec kernel: Buffer I/O error on dev sda, logical block 64, async page read

Details of: /dev/sda

sudo fdisk -l /dev/sda 
Disk /dev/sda: 32 MiB, 33554432 bytes, 65536 sectors
Disk model: Cypress UF2 Boot
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

OS:

Linux Mint 22.2 Zara 
Linux nec 6.14.0-29-generic #29~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Aug 14 16:52:50 UTC 2 x86_64 x86_64 x86_64 GNU/Linu

Regards.

[whitequark]

No partitions should be expected (Windows doesn't support removable USB SCSI devices with partitions); there should be a bare filesystem. But I'm also seeing I/O errors. Are you able to do hd /dev/sda at all?

[hetii]

Yes, I can call hd and get dump but ending with errors:
sudo LANG=C hd /dev/sda:

00000000  eb 3c 90 4d 53 57 49 4e  34 2e 31 00 02 01 01 00  |.<.MSWIN4.1.....|
00000010  01 10 00 00 00 f8 00 01  00 00 00 00 00 00 00 00  |................|
00000020  00 00 01 00 00 00 29 00  00 00 00 43 59 50 52 45  |......)....CYPRE|
00000030  53 53 20 55 46 32 46 41  54 31 36 20 20 20 00 00  |SS UF2FAT16   ..|
00000040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
...
0003fe00  55 53 42 53 93 03 00 00  00 00 00 00 00 00 00 00  |USBS............|
0003fe10  00 01 00 00 00 00 00 00  80 00 00 00 9b 06 18 5a  |...............Z|
0003fe20  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
0003fff0  00 00 00 00 00 00 00 00  00 00 00 00 30 6f b1 0a  |............0o..|
hd: /dev/sda: Input/output error
00040000

tail -f /var/log/syslog

2026-01-08T14:07:04.733069+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK cmd_age=0s
2026-01-08T14:07:04.733080+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Sense Key : Hardware Error [current] 
2026-01-08T14:07:04.733081+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Add. Sense: No additional sense information
2026-01-08T14:07:04.733082+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 CDB: Read(10) 28 00 00 00 01 e0 00 00 f0 00
2026-01-08T14:07:04.733083+01:00 nec kernel: I/O error, dev sda, sector 480 op 0x0:(READ) flags 0x84700 phys_seg 17 prio class 0
2026-01-08T14:07:05.049072+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK cmd_age=0s
2026-01-08T14:07:05.049079+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Sense Key : Hardware Error [current] 
2026-01-08T14:07:05.049080+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Add. Sense: No additional sense information
2026-01-08T14:07:05.049081+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 CDB: Read(10) 28 00 00 00 02 00 00 00 08 00
2026-01-08T14:07:05.049081+01:00 nec kernel: I/O error, dev sda, sector 512 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
2026-01-08T14:07:05.049081+01:00 nec kernel: Buffer I/O error on dev sda, logical block 64, async page read

I see also new usb device icon on my device lists, but double click is not able to mount it:

In shell I was able to mount it by:

mkdir sda
sudo mount /dev/sda sda
ls -al sda/
razem 34
drwxr-xr-x 2 root root   512 sty  1  1970 .
drwxrwxr-x 1 dev  dev    164 sty  8 14:10 ..
-rwxr-xr-x 1 root root 32768 kwi 20  2069 CURRENT.UF2
-r-xr-xr-x 1 root root    82 kwi 20  2069 INDEX.HTM
-r-xr-xr-x 1 root root   118 kwi 20  2069 INFO_UF2.TXT
-r-xr-xr-x 1 root root   351 kwi 20  2069 STATUS.TXT

but the mount operation causes errors to appear in the logs, similar to when hd is called.
I have already replaced the cables with brand new ones and checked the sockets.

[whitequark]

It's not a problem with your system. What causes the issue, I believe, is that certain "unused" sectors return an I/O error when requested. This used to work fine but no longer does, and this is a firmware bug. Try changing this line to return true;:

https://github.com/whitequark/libfx2/blob/29325493f971d3986b2a10e8c729a6e038feb598/firmware/library/uf2fat.c#L234

[hetii]

I change given line, then clean firmware and uf2 and recompile it from scratch.

I'm still able to mount it by manual mount call with below errors in logs:

2026-01-08T14:36:36.367063+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK cmd_age=0s
2026-01-08T14:36:36.367068+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Sense Key : Hardware Error [current] 
2026-01-08T14:36:36.367069+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Add. Sense: No additional sense information
2026-01-08T14:36:36.367071+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 CDB: Read(10) 28 00 00 00 02 00 00 00 08 00
2026-01-08T14:36:36.367071+01:00 nec kernel: I/O error, dev sda, sector 512 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
2026-01-08T14:36:36.443073+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_ERROR driverbyte=DRIVER_OK cmd_age=0s
2026-01-08T14:36:36.443077+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Sense Key : Hardware Error [current] 
2026-01-08T14:36:36.443078+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 Add. Sense: No additional sense information
2026-01-08T14:36:36.443078+01:00 nec kernel: sd 2:0:0:0: [sda] tag#0 CDB: Read(10) 28 00 00 00 02 00 00 00 08 00
2026-01-08T14:36:36.443079+01:00 nec kernel: I/O error, dev sda, sector 512 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
2026-01-08T14:36:36.443079+01:00 nec kernel: Buffer I/O error on dev sda, logical block 64, async page read

[whitequark]

OK, not sure then.

[hetii]

I just recheck again and the errors still popup in logs but the mount by clicking on new usb device in folder view works now, so kind of progress.
Edit:
I was wrong :) The clicking on new usb device works only if I mount it manually first by shell to some folder, so the clicking seems just open the existing mount point instead mount it from scratch.