Hi,
We have a custom board based on IMX6 Sabre Auto. The board supports voltage switching from 3.3 V to 1.8 V using the VSELECT signal in the SD card interfaces. However, when inserting a Lexar 633x 128 GB microSD card and using the hdparm utility the output shows the following ( speed is too slow considering that SDR104 max bus speed is 104 MB/s) :
/dev/mmcblk2: Timing cached reads: 656 MB in 2.00 seconds = 327.47 MB/sec
Timing buffered disk reads: 118 MB in 3.01 seconds = 39.18 MB/sec
We can confirm that the voltage is switching to 1.8V (measuring voltage) and that linux is identifying the microSD card as UHS SDR104 with the following test:
root@localhost:~# cat /sys/kernel/debug/mmc2/ios
clock: 198000000 Hz actual clock: 198000000 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: 0 (1.80 V)
Why is the SD access speed so slow? We are using kernel 3.14.28
Thanks
