Hi Sudhakar, hi Mike, On Tue, Jan 17, 2012 at 1:43 PM, Michael Williamson <michael.william...@criticallink.com> wrote: > On 1/17/2012 12:39 AM, Rajashekhara, Sudhakar wrote: >> We had two options to keep the pll0_sysclk3 frequency under allowable >> limits: >> a. Whenever cpu frequency changes, check whether the current value of >> PLL0_SYSCLK3 is greater than the allowed value and adjust accordingly. >> b. Fix the PLL0_SYSCLK3 divider value at some constant such that at all >> operating points, the frequency is within the allowed value. > >> We did some experiments on the NAND performance with the above two options. >> We found out that except for the case when CPU is operating at 100 MHz, >> there was a minor variation in the performance figures (of the order of >> 2-4%). >> Note that we had implemented CPU freq support for NAND during this >> experiment. >> >> Based on the findings we'll be implementing option 'b' in our next release. >> EMIFA frequency will be fixed at 1/5 of CPU rate. > > Well, that's all fine and swell, except we have OMAP-L138 platforms > (built using the MityDSP-L138 SOM) that use the EMIFA for other > devices than NAND, such as an FPGA (and no SDRAM). Dropping the default > 300 MHz OPP EMIFA speed from 100 MHz down to 60 MHz will directly translate > to a 40% reduction in potential bus bandwidth. If you are making this device > wide, it would really be nice to have an option that is more consistent > with option A and let the platform designer decide what rate the EMIFA > clock should run at based on his hardware requirements.
In my opinion hardcoding OPPs in a SoC specific file (arch/arm/mach-davinci/da850.c) was a bad idea. Setting EMIFA clock to 1/5 of CPU rate may be fine for some boards, but for others it may be a bad decision. How about boards with input clock frequencies other than 24 MHz? Currently the OPP settings are only correct if a 24 MHz quartz or oscillator is used. So I think the OPPs should move out of the SoC specific file. Regards, Christian _______________________________________________ Davinci-linux-open-source mailing list Davinci-linux-open-source@linux.davincidsp.com http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source
