[meta-xilinx] u-boot SPL from QSPI flash

[Mike Looijmans]

> Yeah, but I was thinking today...seems to make more sense to do use the sd
> card for development, cause flashing the SPI is a PITA that requires using the
> Xilinx tools.

I never use them.

I boot from SD card, and program the flash from within linux using "flashcp" 
and "ubiformat" commands.

Takes less than half a minute to completely replace the kernel and rootfs.

For speedy booting, put the bootloaders in the QSPI flash, and set the jumpers 
to boot from flash.

My patches made it so that u-boot will still look for an "autorun.scr" on the 
SD card, so you can boot from SD while getting the bootloader from flash.


I plan on adding UBI support to the bootloader. Then all the partitions - 
except the bootloader ones - can be replaced with one big ubi volume.

This will increase the boot time a bit, but allows everything (fpga image, 
kernel, devicetree) to just live inside the filesystem, and give much better 
wear leveling.

For fastest boot from flash, the thing to do is:
- Use an lzo-compressed squash root filesystem
- Use u-boot SPL to load and start the kernel directly.

I think you can get a "login" prompt in maybe less than 2 seconds then.

Mike.



Met vriendelijke groet / kind regards,

Mike Looijmans

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