[flashrom] [PATCH] Fast flash read speed with FTDI FT2232H programmer

[Stefan Tauner]

On Sun, 18 Jan 2015 08:50:57 +0300
Boris Baykov <dev at borisbaykov.com> wrote:

> 
> The patch increases flash read speed via FTDI FT2232H programmer.
> New ft2232_spi_read function used instead of spi_read_chunked
> to read by 64k chunks instead of 256b chunks.
> 
> According to 3-7 ms FTDI delay for each flash instruction
> this patch makes read operation faster in about 10 times.
> 
> To have stable transfers with 64k buffer SPI frequency should
> be decreased to 5 MHz. I don't know why but higher freqs
> aren't working correct. DEFAULT_DIVISOR is changed to 12.

Hi,

thanks for the patch. I see two major problems with it though. First of
all the divisor problem has to be investigated. I presume you have only
tested with a single hardware setup, right? I'd like to see results from
different dongles/setups... and/or a conclusive theory why the problems
happens at higher frequencies.

The other thing is the incompatibility of the chunk size... yes, a
majority of chips support this, but flashrom prioritizes other things:
stability and compatibility. I don't care for the slowness if that's
the price for it to work universally with all chips in the wild.

The chunk size problem can be fixed in the long run when we come up
with a better infrastructure for this kind of problem (e.g. storing the
maximum read chunk size per chip). However, this is not going to happen
soon. We have more pressing problems and way too many outstanding
patches with a higher priority than speed problems. Therefore I will
not commit anything like this soonish and recommend to keep this patch
or similar ones applied locally if you need it. This is not very
satisfying for anybody but the way it is currently, sorry.

-- 
Kind regards/Mit freundlichen Grüßen, Stefan Tauner