On 04/25/2014 01:58 PM, Viresh Kumar wrote:
> On 25 April 2014 13:48, Srivatsa S. Bhat
> <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote:
>> During frequency transitions, the cpufreq core takes the responsibility of
>> invoking cpufreq_freq_transition_begin() and cpufreq_freq_transition_end()
>> for those cpufreq drivers that define the ->target_index callback but don't
>> set the ASYNC_NOTIFICATION flag.
>>
>> The powernow-k6 cpufreq driver falls under this category, but this driver was
>> invoking the _begin() and _end() APIs itself around frequency transitions,
>> which led to double invocation of the _begin() API. The _begin API makes
>> contending callers wait until the previous invocation is complete. Hence,
>> the powernow-k6 driver ended up waiting on itself, leading to system hangs
>> during boot.
>>
>> Fix this by removing the calls to the _begin() and _end() APIs from the
>> powernow-k6 driver, since they rightly belong to the cpufreq core.
>>
>> (Note that during ->exit(), the powernow-k6 driver sets the frequency
>> without any help from the cpufreq core. So add explicit calls to the
>> _begin() and _end() APIs around that frequency transition alone, to take
>> care of that special case. Also, add a missing 'break' statement there.)
>>
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
>> ---
>>
>> drivers/cpufreq/powernow-k6.c | 20 +++++++++++---------
>> 1 file changed, 11 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/cpufreq/powernow-k6.c b/drivers/cpufreq/powernow-k6.c
>> index 49f120e..6a4c34e 100644
>> --- a/drivers/cpufreq/powernow-k6.c
>> +++ b/drivers/cpufreq/powernow-k6.c
>> @@ -138,22 +138,14 @@ static void powernow_k6_set_cpu_multiplier(unsigned int best_i)
>> static int powernow_k6_target(struct cpufreq_policy *policy,
>> unsigned int best_i)
>> {
>> - struct cpufreq_freqs freqs;
>>
>> if (clock_ratio[best_i].driver_data > max_multiplier) {
>> printk(KERN_ERR PFX "invalid target frequency\n");
>> return -EINVAL;
>> }
>>
>> - freqs.old = busfreq * powernow_k6_get_cpu_multiplier();
>> - freqs.new = busfreq * clock_ratio[best_i].driver_data;
>> -
>> - cpufreq_freq_transition_begin(policy, &freqs);
>> -
>> powernow_k6_set_cpu_multiplier(best_i);
>>
>> - cpufreq_freq_transition_end(policy, &freqs, 0);
>> -
>> return 0;
>> }
>>
>> @@ -228,8 +220,18 @@ static int powernow_k6_cpu_exit(struct cpufreq_policy *policy)
>> {
>> unsigned int i;
>> for (i = 0; i < 8; i++) {
>> - if (i == max_multiplier)
>> + if (i == max_multiplier) {
>
> This wouldn't work, it has to be: (clock_ratio[i].driver_data == max_multiplier)
>
Hmm, looks like an existing bug in the driver. Will fix this in the next
version.
Regards,
Srivatsa S. Bhat
>> + struct cpufreq_freqs freqs;
>> +
>> + freqs.old = policy->cur;
>> + freqs.new = clock_ratio[i].frequency;
>> + freqs.flags = 0;
>> +
>> + cpufreq_freq_transition_begin(policy, &freqs);
>> powernow_k6_target(policy, i);
>> + cpufreq_freq_transition_end(policy, &freqs, 0);
>> + break;
>> + }
>> }
>> return 0;
>> }
>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
>
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