Very slow nor flash write

[Nicolas Pitre]

On Thu, 22 Nov 2007, Alexey Korolev wrote:

> Hi Timo
> 
> > I have an LH7A400 board and there intel 28F160B3T nor flash chip. I managed to configure Linux 2.6.18 to access the chip as an MTD device. However, the write access was very slow, about 40ms per word or 0.00005 MB/s ;-)
> > 
> > I traced the problem to inval_cache_and_wait_for_operation() in cfi_cmdset_0001.c. In the for-loop, if the write access haven't finished when checked for the first time, a long "msleep(sleep_time/1000);" is triggered. The sleep duration is very long because chip_op_time value is 50000. The value comes from "cfi->chips[i].word_write_time = 50000;" in cfi_cmdset_0001(). That is wrong, I think. I changed it to 200 and now the writing is as fast as expected.
> > 
> > Now, the question is: How this should be fixed *correctly*? The 200 is the maximum word program time for this particular chip. Maybe it should have different value for different chips.
> 
> It seems the problem really exists and needs to be solved. The default 
> value of word programming timeo is defined improperly 50000usec for 
> one word is too much - but it is not good to set it very low because 
> inval_cache_and_wait function could return with timeo out error. The 
> best thing would be to set default word programming time for the 
> slowest case. I think 10KB/s would be worst enough case.

No.  You don't know if that is indeed the _absolute_ worst case, and 
doing so just moves the problem elsewhere.

Why not simply adding a fixup entry for this particular flash model to 
override word_write_time with the appropriate value instead?


Nicolas