SD card read speed U-boot vs OS

[Bor]

Hi,

 

U-boot reads my SD card with a speed of less then 1 MB/s.

This is the log from extraPutty for my kernel image:

[30:208][35:648] 5025176 bytes read in 5389 ms (910.2 KiB/s)

I find similar results from other people.

When I read the same file in a shell with dd I get a speed of 20 MB/s.

Clear the cache:

echo 3 > /proc/sys/vm/drop_caches

Read file from the /boot directory:

dd if=zImage of=/dev/null
9814+1 records in
9814+1 records out
5025176 bytes (5.0 MB) copied, 0.246444 s, 20.4 MB/s

This is the result I expect because the hardware is SD v2. (25 MB/s)

Goal: Faster boot by increasing the SD card read speed of U-boot.

Question: How to do this?  

Any remark is appreciated.

 

Regards,

 

Bor.

[zador.blood.stained]

U-boot MMC driver was designed to be small and simple, so it may not handle faster transfer modes, higher clock rates and DMA.

Even relative code size - ~1100 lines in kernel and ~480 lines in u-boot may tell the difference.