Read times drop when increasing frequency to 25 MHz and 50 MHz,
but not in between or for further increase. So, use 50 MHz as the
lowest frequency with the fastest speed.
Test results (thanks to Roger):
The device reports a mx25l6405d flash chip. I tried all the maximum
values in the devices' datasheet (Table 10. AC CHARACTERISTICS). All of
them worked with and without "m25p,fast-read":
> 10 MHz
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 1m 33.00s
user 0m 0.01s
sys 1m 7.56s
> 25 MHz
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 34.42s
user 0m 0.02s
sys 0m 23.58s
> 25 MHz, fast read
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 34.45s
user 0m 0.02s
sys 0m 23.59s
> 33 MHz
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 34.39s
user 0m 0.00s
sys 0m 23.60s
> 33 MHz, fast read
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 34.46s
user 0m 0.01s
sys 0m 23.62s
> 50 MHz
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 26.81s
user 0m 0.01s
sys 0m 18.25s
> 50 MHz, fast read
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 26.84s
user 0m 0.00s
sys 0m 18.25s
> 66 MHz
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 26.80s
user 0m 0.01s
sys 0m 18.23s
> 66 MHz, fast read
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 26.80s
user 0m 0.02s
sys 0m 18.23s
> 86 MHz
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 26.84s
user 0m 0.01s
sys 0m 18.24s
> 86 MHz, fast read
root@OpenWrt:~# time cat /dev/mtd* > /dev/null
real 0m 26.80s
user 0m 0.02s
sys 0m 18.23s
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Tested-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>
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