[PATCH V2] cpufreq: ARM big LITTLE: Add generic cpufreq driver and its DT glue
Guennadi Liakhovetski
g.liakhovetski at gmx.de
Thu Mar 7 16:56:54 EST 2013
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/
More information about the linux-arm-kernel
mailing list