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Date: Mon, 23 Sep 2019 14:01:02 +0100
From: Jon Hunter <jonathanh@...dia.com>
To: Dmitry Osipenko <digetx@...il.com>,
Thierry Reding <thierry.reding@...il.com>,
Peter De Schrijver <pdeschrijver@...dia.com>
CC: <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] soc/tegra: pmc: Query PCLK clock rate at probe
time
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@...il.com>
>>> ---
>>>
>>> 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).
Jon
--
nvpublic
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