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/