Re: [PATCH AUTOSEL 4.19 123/158] cpufreq: Don't skip frequency validation for has_target() drivers

Sasha Levin
2019-07-22T00:40:40Z

On Tue, Jul 16, 2019 at 11:21:34AM +0200, Rafael J. Wysocki wrote:
>On 7/15/2019 4:17 PM, Sasha Levin wrote:
>>From: Viresh Kumar <viresh.kumar@linaro.org>
>>
>>[ Upstream commit 9801522840cc1073f8064b4c979b7b6995c74bca ]
>>
>>CPUFREQ_CONST_LOOPS was introduced in a very old commit from pre-2.6
>>kernel release by commit 6a4a93f9c0d5 ("[CPUFREQ] Fix 'out of sync'
>>issue").
>>
>>Basically, that commit does two things:
>>
>> - It adds the frequency verification code (which is quite similar to
>> what we have today as well).
>>
>> - And it sets the CPUFREQ_CONST_LOOPS flag only for setpolicy drivers,
>> rightly so based on the code we had then. The idea was to avoid
>> frequency validation for setpolicy drivers as the cpufreq core doesn't
>> know what frequency the hardware is running at and so no point in
>> doing frequency verification.
>>
>>The problem happened when we started to use the same CPUFREQ_CONST_LOOPS
>>flag for constant loops-per-jiffy thing as well and many has_target()
>>drivers started using the same flag and unknowingly skipped the
>>verification of frequency. There is no logical reason behind skipping
>>frequency validation because of the presence of CPUFREQ_CONST_LOOPS
>>flag otherwise.
>>
>>Fix this issue by skipping frequency validation only for setpolicy
>>drivers and always doing it for has_target() drivers irrespective of
>>the presence or absence of CPUFREQ_CONST_LOOPS flag.
>>
>>cpufreq_notify_transition() is only called for has_target() type driver
>>and not for set_policy type, and the check is simply redundant. Remove
>>it as well.
>>
>>Also remove () around freq comparison statement as they aren't required
>>and checkpatch also warns for them.
>>
>>Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
>>Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>Signed-off-by: Sasha Levin <sashal@kernel.org>
>>---
>> drivers/cpufreq/cpufreq.c | 13 +++++--------
>> 1 file changed, 5 insertions(+), 8 deletions(-)
>>
>>diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>index d3213594d1a7..80942ec34efd 100644
>>--- a/drivers/cpufreq/cpufreq.c
>>+++ b/drivers/cpufreq/cpufreq.c
>>@@ -321,12 +321,10 @@ static void cpufreq_notify_transition(struct cpufreq_policy *policy,
>> * which is not equal to what the cpufreq core thinks is
>> * "old frequency".
>> */
>>- if (!(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
>>- if (policy->cur && (policy->cur != freqs->old)) {
>>- pr_debug("Warning: CPU frequency is %u, cpufreq assumed %u kHz\n",
>>- freqs->old, policy->cur);
>>- freqs->old = policy->cur;
>>- }
>>+ if (policy->cur && policy->cur != freqs->old) {
>>+ pr_debug("Warning: CPU frequency is %u, cpufreq assumed %u kHz\n",
>>+ freqs->old, policy->cur);
>>+ freqs->old = policy->cur;
>> }
>> for_each_cpu(freqs->cpu, policy->cpus) {
>>@@ -1543,8 +1541,7 @@ static unsigned int __cpufreq_get(struct cpufreq_policy *policy)
>> if (policy->fast_switch_enabled)
>> return ret_freq;
>>- if (ret_freq && policy->cur &&
>>- !(cpufreq_driver->flags & CPUFREQ_CONST_LOOPS)) {
>>+ if (has_target() && ret_freq && policy->cur) {
>> /* verify no discrepancy between actual and
>> saved value exists */
>> if (unlikely(ret_freq != policy->cur)) {
>
>This is not -stable material, please drop it.

I've dropped it, thanks!

--
Thanks,
Sasha