23.09.2019 16:31, Dmitry Osipenko пишет:
> 23.09.2019 16:01, Jon Hunter пишет:
>>
>> On 23/09/2019 13:49, Dmitry Osipenko wrote:
>>> 23.09.2019 13:56, Jon Hunter пишет:
>>>>
>>>>
>>>> On 04/08/2019 21:29, Dmitry Osipenko wrote:
>>>>> It is possible to get a lockup if kernel decides to enter LP2 cpuidle
>>>>> from some clk-notifier, in that case CCF's "prepare" mutex is kept locked
>>>>> and thus clk_get_rate(pclk) blocks on the same mutex with interrupts being
>>>>> disabled.
>>>>>
>>>>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
>>>>> ---
>>>>>
>>>>> Changelog:
>>>>>
>>>>> v4: Added clk-notifier to track PCLK rate-changes, which may become useful
>>>>> in the future. That's done in response to v3 review comment from Peter
>>>>> De Schrijver.
>>>>>
>>>>> Now properly handling case where clk pointer is intentionally NULL on
>>>>> the driver's probe.
>>>>>
>>>>> v3: Changed commit's message because I actually recalled what was the
>>>>> initial reason for the patch, since the problem reoccurred once again.
>>>>>
>>>>> v2: Addressed review comments that were made by Jon Hunter to v1 by
>>>>> not moving the memory barrier, replacing one missed clk_get_rate()
>>>>> with pmc->rate, handling possible clk_get_rate() error on probe and
>>>>> slightly adjusting the commits message.
>>>>>
>>>>> drivers/soc/tegra/pmc.c | 71 ++++++++++++++++++++++++++++++-----------
>>>>> 1 file changed, 53 insertions(+), 18 deletions(-)
>>>>>
>>>>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>>>>> index 9f9c1c677cf4..4e44943d0b26 100644
>>>>> --- a/drivers/soc/tegra/pmc.c
>>>>> +++ b/drivers/soc/tegra/pmc.c
>>>>> @@ -309,6 +309,7 @@ static const char * const tegra210_reset_sources[] = {
>>>>> * @pctl_dev: pin controller exposed by the PMC
>>>>> * @domain: IRQ domain provided by the PMC
>>>>> * @irq: chip implementation for the IRQ domain
>>>>> + * @clk_nb: pclk clock changes handler
>>>>> */
>>>>> struct tegra_pmc {
>>>>> struct device *dev;
>>>>> @@ -344,6 +345,8 @@ struct tegra_pmc {
>>>>>
>>>>> struct irq_domain *domain;
>>>>> struct irq_chip irq;
>>>>> +
>>>>> + struct notifier_block clk_nb;
>>>>> };
>>>>>
>>>>> static struct tegra_pmc *pmc = &(struct tegra_pmc) {
>>>>> @@ -1192,7 +1195,7 @@ static int tegra_io_pad_prepare(struct tegra_pmc *pmc, enum tegra_io_pad id,
>>>>> return err;
>>>>>
>>>>> if (pmc->clk) {
>>>>> - rate = clk_get_rate(pmc->clk);
>>>>> + rate = pmc->rate;
>>>>> if (!rate) {
>>>>> dev_err(pmc->dev, "failed to get clock rate\n");
>>>>> return -ENODEV;
>>>>
>>>> So this error should never happen now, right? Assuming that rate is
>>>> never set to 0. But ...
>>>
>>> Good catch!
>>>
>>>>> @@ -1433,6 +1436,7 @@ void tegra_pmc_set_suspend_mode(enum tegra_suspend_mode mode)
>>>>> void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>>>>> {
>>>>> unsigned long long rate = 0;
>>>>> + u64 ticks;
>>>>> u32 value;
>>>>>
>>>>> switch (mode) {
>>>>> @@ -1441,31 +1445,22 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>>>>> break;
>>>>>
>>>>> case TEGRA_SUSPEND_LP2:
>>>>> - rate = clk_get_rate(pmc->clk);
>>>>> + rate = pmc->rate;
>>>>> break;
>>>>>
>>>>> default:
>>>>> break;
>>>>> }
>>>>>
>>>>> - if (WARN_ON_ONCE(rate == 0))
>>>>> - rate = 100000000;
>>>>> -
>>>>> - if (rate != pmc->rate) {
>>>>> - u64 ticks;
>>>>> -
>>>>> - ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
>>>>> - do_div(ticks, USEC_PER_SEC);
>>>>> - tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
>>>>> + ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
>>>>> + do_div(ticks, USEC_PER_SEC);
>>>>> + tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
>>>>>
>>>>> - ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
>>>>> - do_div(ticks, USEC_PER_SEC);
>>>>> - tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
>>>>> + ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
>>>>> + do_div(ticks, USEC_PER_SEC);
>>>>> + tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
>>>>>
>>>>> - wmb();
>>>>> -
>>>>> - pmc->rate = rate;
>>>>> - }
>>>>> + wmb();
>>>>>
>>>>> value = tegra_pmc_readl(pmc, PMC_CNTRL);
>>>>> value &= ~PMC_CNTRL_SIDE_EFFECT_LP0;
>>>>> @@ -2019,6 +2014,20 @@ static int tegra_pmc_irq_init(struct tegra_pmc *pmc)
>>>>> return 0;
>>>>> }
>>>>>
>>>>> +static int tegra_pmc_clk_notify_cb(struct notifier_block *nb,
>>>>> + unsigned long action, void *ptr)
>>>>> +{
>>>>> + struct clk_notifier_data *data = ptr;
>>>>> + struct tegra_pmc *pmc;
>>>>> +
>>>>> + if (action == POST_RATE_CHANGE) {
>>>>> + pmc = container_of(nb, struct tegra_pmc, clk_nb);
>>>>> + pmc->rate = data->new_rate;
>>>>> + }
>>>>> +
>>>>> + return NOTIFY_OK;
>>>>> +}
>>>>> +
>>>>> static int tegra_pmc_probe(struct platform_device *pdev)
>>>>> {
>>>>> void __iomem *base;
>>>>> @@ -2082,6 +2091,30 @@ static int tegra_pmc_probe(struct platform_device *pdev)
>>>>> pmc->clk = NULL;
>>>>> }
>>>>>
>>>>> + /*
>>>>> + * PCLK clock rate can't be retrieved using CLK API because it
>>>>> + * causes lockup if CPU enters LP2 idle state from some other
>>>>> + * CLK notifier, hence we're caching the rate's value locally.
>>>>> + */
>>>>> + if (pmc->clk) {
>>>>> + pmc->clk_nb.notifier_call = tegra_pmc_clk_notify_cb;
>>>>> + err = clk_notifier_register(pmc->clk, &pmc->clk_nb);
>>>>> + if (err) {
>>>>> + dev_err(&pdev->dev,
>>>>> + "failed to register clk notifier\n");
>>>>> + return err;
>>>>> + }
>>>>> +
>>>>> + pmc->rate = clk_get_rate(pmc->clk);
>>>>> + }
>>>>> +
>>>>> + if (!pmc->rate) {
>>>>> + if (pmc->clk)
>>>>> + dev_err(&pdev->dev, "failed to get pclk rate\n");
>>>>> +
>>>>> + pmc->rate = 100000000;
>>>>
>>>> I wonder if we should just let this fail. Or set to 0 so that if the
>>>> rate is not set we will never suspend or configure the IO pads? I could
>>>> run some quick tests to see if there are any problems by failing here.
>>>
>>> Do you mean to fail the PMC driver to probe? I guess that will be fatal
>>> and system won't be in a useful state, from a user perspective that
>>> should be equal to a hang on boot with a black screen. On the other
>>> hand, it seems that failing tegra_io_pad_prepare() should have similar
>>> fatal result.
>>>
>>> I'm wondering whether that IO PAD misconfiguration could be harmful. If
>>> not, then looks like falling back to 100Mhz should be good enough. In
>>> practice clk_get_rate() shouldn't ever fail unless there is some serious
>>> bug in clk/. What do you think?
>>
>> Exactly. I think that if clk_get_rate() is failing then something bad is
>> happening. I can see if this causes any obvious problems across the
>> different boards we test, but it would be great to get rid of this
>> 100MHz value (unless Peter knows of a good reason to keep it).
>
> Okay!
>
> Peter, do you have any thoughts about whether it worth to keep the
> 100MHz workaround?
>
> BTW.. looking at tegra_io_pad_prepare() again, I think that it should be
> fine to simply keep the clk_get_rate() there.
[it will be fine without having the clk notifier or without the locking
within the notifier that I suggested below]
> It also looks like clk notifier should actually take powergates_lock to
> be really robust and not potentially race with tegra_io_pad_prepare(). I
> can fix up it in v5, but.. maybe it will be better to postpone the clk
> notifier addition until there will be a real use-case for PMC clk
> freq-scaling and for now assume that clk rate is static?
>
