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SubjectRe: [PATCH v2 12/19] PM / devfreq: tegra: Avoid inconsistency of current frequency value
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Date
Hi,

On 19. 4. 15. 오후 11:54, Dmitry Osipenko wrote:
> The frequency value potentially could change in-between. It doesn't
> cause any real problem at all right now, but that could change in the
> future. Hence let's avoid the inconsistency.
>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
> drivers/devfreq/tegra-devfreq.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
> index a668e4fbc874..f1a6f951813a 100644
> --- a/drivers/devfreq/tegra-devfreq.c
> +++ b/drivers/devfreq/tegra-devfreq.c
> @@ -496,13 +496,15 @@ static int tegra_devfreq_get_dev_status(struct device *dev,
> {
> struct tegra_devfreq *tegra = dev_get_drvdata(dev);
> struct tegra_devfreq_device *actmon_dev;
> + unsigned long cur_freq;
>
> - stat->current_frequency = tegra->cur_freq * KHZ;
> + cur_freq = READ_ONCE(tegra->cur_freq);
>
> /* To be used by the tegra governor */
> stat->private_data = tegra;
>
> /* The below are to be used by the other governors */
> + stat->current_frequency = cur_freq * KHZ;
>
> actmon_dev = &tegra->devices[MCALL];
>
> @@ -513,7 +515,7 @@ static int tegra_devfreq_get_dev_status(struct device *dev,
> stat->busy_time *= 100 / BUS_SATURATION_RATIO;
>
> /* Number of cycles in a sampling period */
> - stat->total_time = ACTMON_SAMPLING_PERIOD * tegra->cur_freq;
> + stat->total_time = ACTMON_SAMPLING_PERIOD * cur_freq;
>
> stat->busy_time = min(stat->busy_time, stat->total_time);
>
>

The read/write access of tegra->cur_freq is in the single routine
of update_devfreq() as following. I think that there are no any
potential problem about the inconsistency of tegra->cur_freq.

IMHO, if there are no any problem now, I'm not sure that we need
to apply this patch.

update_devfreq()
{
devfreq->governor->get_target_freq()
devfreq_update_stats(devfreq)
tegra_devfreq_get_dev_status()
stat->current_frequency = tegra->cur_freq * KHZ;

devfreq_set_target()
tegra_devfreq_target()
clk_set_min_rate(emc_rate, )
tegra_actmon_rate_notify_cb()
tegra->cur_freq = data->new_rate / KHZ;

clk_set_rate(emc_rate, )
tegra_actmon_rate_notify_cb()
tegra->cur_freq = data->new_rate / KHZ;
}


--
Best Regards,
Chanwoo Choi
Samsung Electronics

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