"Bedia, Vaibhav" <vaibhav.bedia@xxxxxx> writes: > Hi Kevin, > > On Sat, Dec 03, 2011 at 03:57:57, Hilman, Kevin wrote: > [...] >> > >> > Any comments on this approach? >> >> Sorry, I didn't see this patch before, and I don't see it in the >> linux-omap archives either. Not sure what happened there... >> >> > This enables us to make use of generic regulators calls from the >> > voltage layer. >> >> From this patch, I don't see how the regulator API is being used from >> the voltage layer, so I don't fully understand what you're trying to >> achieve. >> >> IOW, why should the voltagedomain code be calling the regulator API? >> >> The voltage domain code was designed with the opposite goal: namely, >> that a regulator driver would be calling the voltage domain layer, not >> vice versa. > > Sorry, I should have posted more detail on how we are making use of the > change proposed here and how it helps in getting cpufreq and DVFS working. > > We want to use the existing OMAP implementation of cpufreq (and DVFS) on > the devices which do not have VC/VP. > > The current OMAP cpufreq code under drivers/ invokes clk_set_rate(). > > We had a look at the future DVFS implementation for OMAP[1] and merged in > the relevant patches (hope this is close to what's planned). Unfortunately, that implementation is not what's planned, and in fact was rejected some time ago. > After this change, cpufreq invokes omap_device_scale(). The DVFS code > makes use of the OPP layer and adds a request for voltage and frequency > change. However, the voltage change request expects the scaling to be done > in scaling functions defined in the voltage layer (vc->scale or vp->scale) > > On devices which do not have VC/VP, instead of just hacking the current > implementation to get the voltage scaling done, we thought of adding > a separate path. A much better path for SoCs without VC/VP is to simply modify the CPUfreq driver to use the regulator API to scale voltage before calling clk_set_rate() (if scaling up) and after scaling the frequency (if scaling down.) In fact, that is the direction we're going for DVFS, even for VC/VP platforms. There will be a regulator driver which will call the voltagedomain/VC/VP calls to scale the voltage when needed, so from a DVFS perspective, you use the clock API to change frequency, and the regulator API to change voltages. This should be a much simpler approach for you, and much easier to understand. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
