Re: [PATCH v4 02/24] PM / devfreq: tegra30: Keep interrupt disabled while governor is stopped

Dmitry Osipenko
2019-07-17T16:44:18Z

17.07.2019 9:37, Chanwoo Choi пишет:
> On 19. 7. 16. 오후 10:03, Dmitry Osipenko wrote:
>> 16.07.2019 14:47, Chanwoo Choi пишет:
>>> On 19. 7. 8. 오전 7:32, Dmitry Osipenko wrote:
>>>> There is no real need to keep interrupt always-enabled, will be nicer
>>>> to keep it disabled while governor is inactive.
>>>>
>>>> Suggested-by: Thierry Reding <thierry.reding@gmail.com>
>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>>>> ---
>>>> drivers/devfreq/tegra30-devfreq.c | 43 ++++++++++++++++---------------
>>>> 1 file changed, 22 insertions(+), 21 deletions(-)
>>>>
>>>> diff --git a/drivers/devfreq/tegra30-devfreq.c b/drivers/devfreq/tegra30-devfreq.c
>>>> index a27300f40b0b..5e2b133babdd 100644
>>>> --- a/drivers/devfreq/tegra30-devfreq.c
>>>> +++ b/drivers/devfreq/tegra30-devfreq.c
>>>> @@ -11,6 +11,7 @@
>>>> #include <linux/devfreq.h>
>>>> #include <linux/interrupt.h>
>>>> #include <linux/io.h>
>>>> +#include <linux/irq.h>
>>>> #include <linux/module.h>
>>>> #include <linux/mod_devicetable.h>
>>>> #include <linux/platform_device.h>
>>>> @@ -416,8 +417,6 @@ static void tegra_actmon_start(struct tegra_devfreq *tegra)
>>>> {
>>>> unsigned int i;
>>>>
>>>> - disable_irq(tegra->irq);
>>>> -
>>>> actmon_writel(tegra, ACTMON_SAMPLING_PERIOD - 1,
>>>> ACTMON_GLB_PERIOD_CTRL);
>>>>
>>>> @@ -442,8 +441,6 @@ static void tegra_actmon_stop(struct tegra_devfreq *tegra)
>>>> }
>>>>
>>>> actmon_write_barrier(tegra);
>>>> -
>>>> - enable_irq(tegra->irq);
>>>> }
>>>>
>>>> static int tegra_devfreq_target(struct device *dev, unsigned long *freq,
>>>> @@ -552,6 +549,12 @@ static int tegra_governor_event_handler(struct devfreq *devfreq,
>>>> {
>>>> struct tegra_devfreq *tegra = dev_get_drvdata(devfreq->dev.parent);
>>>>
>>>> + /*
>>>> + * Couple device with the governor early as it is needed at
>>>> + * the moment of governor's start (used by ISR).
>>>> + */
>>>> + tegra->devfreq = devfreq;
>>>
>>> I'm not sure it is necessary. Almost devfreq device get
>>> the devfreq instance on probe timing through devfreq_add_device directly.
>>
>> This is necessary because this assignment is for the "governor" and not
>> the "device". Governor is started during of devfreq_add_device(), hence
>> there is no better way to assign device to the driver's governor.
>
> OK. I understand.
>
> But, I have a question. Is it working before this patch?
> How can you test it on that tegra->devfreq is NULL?

It was working before this patch because previously interrupt was
requested *after* devfreq_add_device(), now the IRQ requesting happens
*before* devfreq_add_device() and enabling *during of*. If interrupt
fires before the assignment happened, then ISR gets a NULL deference and
this is easily reproducible.

Please note that 'tegra->devfreq' is used only by the ISR and onward, in
the further patches of this series the usage is extended by the cpufreq
notifier.

>>
>>>> +
>>>> switch (event) {
>>>> case DEVFREQ_GOV_START:
>>>> devfreq_monitor_start(devfreq);
>>>> @@ -586,10 +589,11 @@ static struct devfreq_governor tegra_devfreq_governor = {
>>>>
>>>> static int tegra_devfreq_probe(struct platform_device *pdev)
>>>> {
>>>> - struct tegra_devfreq *tegra;
>>>> struct tegra_devfreq_device *dev;
>>>> - unsigned int i;
>>>> + struct tegra_devfreq *tegra;
>>>> + struct devfreq *devfreq;
>>>> unsigned long rate;
>>>> + unsigned int i;
>>>> int err;
>>>>
>>>> tegra = devm_kzalloc(&pdev->dev, sizeof(*tegra), GFP_KERNEL);
>>>> @@ -625,6 +629,16 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>>>> }
>>>> tegra->irq = err;
>>>>
>>>> + irq_set_status_flags(tegra->irq, IRQ_NOAUTOEN);
>>>> +
>>>> + err = devm_request_threaded_irq(&pdev->dev, tegra->irq, NULL,
>>>> + actmon_thread_isr, IRQF_ONESHOT,
>>>> + "tegra-devfreq", tegra);
>>>> + if (err) {
>>>> + dev_err(&pdev->dev, "Interrupt request failed: %d\n", err);
>>>> + return err;
>>>> + }
>>>> +
>>>> reset_control_assert(tegra->reset);
>>>>
>>>> err = clk_prepare_enable(tegra->clock);
>>>> @@ -672,28 +686,15 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>>>> }
>>>>
>>>> tegra_devfreq_profile.initial_freq = clk_get_rate(tegra->emc_clock);
>>>> - tegra->devfreq = devfreq_add_device(&pdev->dev,
>>>> - &tegra_devfreq_profile,
>>>> - "tegra_actmon",
>>>> - NULL);
>>>> + devfreq = devfreq_add_device(&pdev->dev, &tegra_devfreq_profile,
>>>> + "tegra_actmon", NULL);
>>>> if (IS_ERR(tegra->devfreq)) {
>>>
>>> Have to check 'devfreq' instead of 'tegra->devfreq'.
>>> Did you test it? It might be failed because 'tegra->devfreq is NULL.
>>
>> That's a good catch! Thank you very much.
>>
>>>> err = PTR_ERR(tegra->devfreq);
>>>
>>> ditto.
>>
>> Ok