[flashrom] performance of flashrom (with FT2232H)

[Stefan Tauner]

On Wed, 14 Jan 2015 16:23:32 +0300
"Amelkin,  Aleksandr" <Aleksandr.Amelkin at t-platforms.ru> wrote:

> I noticed that it takes painfully long for flashrom to even simply read a 16MB flash chip
> using FT2232H (Olimex ARM-USB-TINY-H) programmer.
> 
> The time it takes would be appropriate for kHz-range SPI clocks, not for 30MHz SPI clock
> that FT2232H provides.
> 
> I checked with an oscilloscope and found out that there are long multi-millisecond delays between short (~150us) SPI clock bursts during simple chip read operation ('-r' or 'reading old flash chip contents'). The delays are 2ms for native Windows 7 64-bit on an Intel Core-i7 2600 @ 3.4GHz, or as long as 7ms for a Ubuntu Linux running in a virtual box on the same Windows machine.
> 
> I didn't look any deeper though.
> 
> Has anyone done any profiling or have any ideas as to what may be causing this behavior?

I suspect the main part of this is the latency of the (FTDI) USB
protocol. Maybe the performance of the flashrom driver can be improved
with bigger buffers/bursts of reads but I am not aware of any obvious
bottlenecks.

-- 
Kind regards/Mit freundlichen Grüßen, Stefan Tauner