flash read performance

[Andre Puschmann]

Hi,

> I was faced with the same wondering in the past : bootloader NOR access 
> was really much faster that Linux one.

About how much faster? It really depends on the access method. I am
using u-boot and if I use the basic cp.b routine its about the same
_slow_ speed. I tried to use the asm-optimised memcpy routine that the 
kernel has. This is much faster, around 5MB/s.

> Yes, no DMA was used (but the same on bootloader, and anyway that 
> doesn't impact the data rate, only the CPU load), but even worse, Linux 
> code was using memcpy_fromio which a basic byte by byte loop copy in the 
> default ARM implementation.

Yes, memcpy_fromio is quite slow. But using normal memcpy is not 
suggested, only use writel()/readl() and memcpy_[from|to]io().

I am not sure about the right _fast_ way to to such copies.


Regards,
Andre