Tony Lindgren wrote:
* Mike Rapoport <mike.rapop...@gmail.com> [100503 13:28]:
So it comes down to what provides better tolerance, the explicit NAND
timings in nanosecs or (rounded) timings in ticks derived from
bootloader settings...
My experience is that you can get the nanosec timings from the device
datasheet(s) and that just should work for any L3 frequency.
And what about boards that can have different NAND flash chips
assembled? What datasheet should be used to get the nanosecs? Note, that
detecting NAND ID in the bootloader and adjusting timings appropriately
is not that big deal, and doing it in the kernel seems to me really
impractical.
My experience is also that trying to do it the other way around won't work
because of rounding errors. Trying to produce nanosecond values out
of the tick values just is not accurate enough.
I'm still not convinced. Similar approach worked for me with several
devices attached to sort of GPMC controllers on different SoC. There
always was a way to set timings once in the bootloader and then detect
the timings in the kernel and update them during cpu-freq transitions...
That's why gpmc-onenand.c and usb-tusb6010.c timings are done the way
they are, and they're known to work at various L3 frequencies.
I'm not really familiar with OneNAND, but looking at gpmc-onenand.c I
see hardcoded timings. Moreover, the nanosecs values seem to get
adjusted for different L3 frequencies.
So, for NAND it would mean that platform would have to supply several
timing sets for different L3 freqs?
So maybe just not do anything, and print a warning on gpmc L3 changes
if the timings are not set?
I don't quite understand where exactly this warning should go. I
haven't found any treatment of L3 frequency changes in gpmc related
code neither in linux-omap nor in linux-omap-pm...
Ah, right. There's currently nothing doing that.. That would have to
be done based on cpufreq notifiers (or clock notifiers). But we don't
have any of that at least in the mainline yet. Hmm I don't even think
we currently scale the L3 for cpufreq.. Right now the best way to test
would be by booting at different L3 frequencies.
Anyways, my point is that setting gpmc_default_timings based on the
bootloader after doing the gpmc_cs_get_timings is most likely unsafe
for other L3 frequencies.
Regards,
Tony
--
Sincerely yours,
Mike.
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