Hi Viresh On Fri, 8 Mar 2013, Viresh Kumar wrote:
> big LITTLE is ARM's new Architecture focussing power/performance needs of > modern > world. More information about big LITTLE can be found here: > > http://www.arm.com/products/processors/technologies/biglittleprocessing.php > http://lwn.net/Articles/481055/ > > In order to keep cpufreq support for all big LITTLE platforms simple/generic, > this patch tries to add a generic cpufreq driver layer for all big LITTLE > platforms. I like generic drivers :) cpufreq-cpu0 is yet another such generic (cpufreq) driver. Now, comparing the functionality of the two: [snip] > +/* Set clock frequency */ > +static int bL_cpufreq_set_target(struct cpufreq_policy *policy, > + unsigned int target_freq, unsigned int relation) > +{ > + struct cpufreq_freqs freqs; > + u32 cpu = policy->cpu, freq_tab_idx, cur_cluster; > + int ret = 0; > + > + cur_cluster = cpu_to_cluster(policy->cpu); > + > + freqs.old = bL_cpufreq_get(policy->cpu); > + > + /* Determine valid target frequency using freq_table */ > + cpufreq_frequency_table_target(policy, freq_table[cur_cluster], > + target_freq, relation, &freq_tab_idx); > + freqs.new = freq_table[cur_cluster][freq_tab_idx].frequency; > + > + freqs.cpu = policy->cpu; > + > + pr_debug("%s: cpu: %d, cluster: %d, oldfreq: %d, target freq: %d, new > freq: %d\n", > + __func__, cpu, cur_cluster, freqs.old, target_freq, > + freqs.new); > + > + if (freqs.old == freqs.new) > + return 0; > + > + for_each_cpu(freqs.cpu, policy->cpus) > + cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE); > + > + ret = clk_set_rate(clk[cur_cluster], freqs.new * 1000); we see, that this driver "only" switches CPU clock frequencies. Whereas the cpufreq-cpu0 driver also manipulates a regulator (if available) directly. I understand, power-saving is also an important consideration for big.LITTLE systems. So, I presume, you plan to implement voltage switching in cpufreq notifiers? Now, my question is: is this (notifier) actually the preferred method and the cpufreq-cpu0 driver is doing it "wrongly?" Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
