Slow SD card access speed (read+write) with Jetson Nano production module

Hi WayneWWW,

We ran into some issues because of which I had to reopen this ticket, sorry. The thing is my dtb changes take into effect only after a hard reboot (power off + on). But when I do a soft reboot, the dtb changes related to SD card speed are not reflected and they show some older dtb values. For instance, when I do a soft reboot, and then check the ios, I get the following output:

cat /sys/kernel/debug/mmc1/ios
clock:		50000000 Hz
vdd:		21 (3.3 ~ 3.4 V)
bus mode:	2 (push-pull)
chip select:	0 (don't care)
power mode:	2 (on)
bus width:	2 (4 bits)
timing spec:	2 (sd high-speed)
signal voltage:	0 (3.30 V)
driver type:	0 (driver type B)

But I have changed the dtb already before flashing, so this should not be the case. Instead what I should get as an output is the following, which I also get with a hard reboot (power off+on).

cat /sys/kernel/debug/mmc1/ios    
clock:		204000000 Hz
vdd:		21 (3.3 ~ 3.4 V)
bus mode:	2 (push-pull)
chip select:	0 (don't care)
power mode:	2 (on)
bus width:	2 (4 bits)
timing spec:	6 (sd uhs SDR104)
signal voltage:	1 (1.80 V)
driver type:	0 (driver type B)

It seems an old dtb is loaded from somewhere which I need to prevent. How do I do this? For the soft reboot case, I also observe that the SD card access speeds are actually slower 4 times (like 23 MBps vs 85 MBps on a hard reboot), when tested with the gnome-disks benchmarking utility that I mentioned before.