I also have slow read/write SD card speed on production SOM (b00) after I have followed the link below.
Link that I have followed: Slow SD card access speed (read+write) with Jetson Nano production module
My System: Production Nano SOM (b00) with custom carrier board.
SDK Manager with Jetpack 4.4.1
SD Card mount permanent (non-removable)
tried by editing tegra210-p3448-0002-p3449-0000-b00.dts file by:
added: sd-uhs-sdr104.50,25, and 12
deleted: max-clk-limit = <400000>;
sudo ./flash -r -k DTB mmcblk0p1
Check dmesg and clock speed:
Did not find "new ultra high speed SDR104 SDXC card " in dmesg
cat /sys/kernel/debug/mmc1/clock: 9,600,000 (not 204MHz)
cat /sys/kernel/debug/mmc1/ios: 9,600,000
cat /sys/kernel/debug/mmc1/speed: 1