soc/tegra: pmc: Query PCLK clock rate at probe time

The PCLK clock is running off SCLK, which is a critical clock that is very unlikely to randomly change its rate. It's also a bit clumsy (and apparently incorrect) to query the clock's rate with interrupts being disabled because clk_get_rate() takes a mutex and that's the case during suspend/cpuidle entering.

Signed-off-by Dmitry Osipenko <[email protected]>

---

Changelog:

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 | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

drivers/soc/tegra/pmc.c +16 -18

index 9f9c1c677cf4..aba3396b2e73 100644
@@ -1192,7 +1192,7 @@ 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;

@@ -1433,6 +1433,7 @@ 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 +1442,22 @@ 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;
+	ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
+	do_div(ticks, USEC_PER_SEC);
+	tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
 
-	if (rate != pmc->rate) {
-		u64 ticks;
+	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_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);
-
-		wmb();
-
-		pmc->rate = rate;
-	}
+	wmb();
 
 	value = tegra_pmc_readl(pmc, PMC_CNTRL);
 	value &= ~PMC_CNTRL_SIDE_EFFECT_LP0;

@@ -2082,8 +2074,14 @@ static int tegra_pmc_probe(struct platform_device *pdev)
 		pmc->clk = NULL;
 	}
 
+	pmc->rate = clk_get_rate(pmc->clk);
 	pmc->dev = &pdev->dev;
 
+	if (!pmc->rate) {
+		dev_err(&pdev->dev, "failed to get pclk rate\n");
+		pmc->rate = 100000000;
+	}
+
 	tegra_pmc_init(pmc);
 
 	tegra_pmc_init_tsense_reset(pmc);

Signature · 1 line

2.22.0

Quoted 6 lines

The PCLK clock is running off SCLK, which is a critical clock that is very unlikely to randomly change its rate. It's also a bit clumsy (and apparently incorrect) to query the clock's rate with interrupts being disabled because clk_get_rate() takes a mutex and that's the case during suspend/cpuidle entering.

SCLK and PCLK certainly can change rate at runtime, although the code to handle this hasn't reached upstream yet.

25.07.2019 12:36, Peter De Schrijver пишет:

Quoted 8 lines · Dmitry Osipenko

Quoted 6 lines

The PCLK clock is running off SCLK, which is a critical clock that is very unlikely to randomly change its rate. It's also a bit clumsy (and apparently incorrect) to query the clock's rate with interrupts being disabled because clk_get_rate() takes a mutex and that's the case during suspend/cpuidle entering.

Quoted 2 lines

SCLK and PCLK certainly can change rate at runtime, although the code to handle this hasn't reached upstream yet.

Okay, maybe this patch is indeed not very worthwhile then. I'm leaving it up to you, guys, to decide.

25.07.2019 14:15, Dmitry Osipenko пишет:

Quoted 9 lines

25.07.2019 12:36, Peter De Schrijver пишет:

Quoted 8 lines · Dmitry Osipenko

Quoted 6 lines

The PCLK clock is running off SCLK, which is a critical clock that is very unlikely to randomly change its rate. It's also a bit clumsy (and apparently incorrect) to query the clock's rate with interrupts being disabled because clk_get_rate() takes a mutex and that's the case during suspend/cpuidle entering.

Quoted 6 lines

Quoted 2 lines

SCLK and PCLK certainly can change rate at runtime, although the code to handle this hasn't reached upstream yet.

Okay, maybe this patch is indeed not very worthwhile then. I'm leaving it up to you, guys, to decide.

I now recalled what was the initial reason for this patch because happened to bump into the problem once again.. it's really problematic to call clk_get_rate() with the disabled preemption because some clk notifier handler may block (EMC) and cause reschedule, hence the CCF 'prepare' mutex is kept locked during of CPUIDLE driver entering LP2 state and thus causing system lockup, since scheduling with the disabled interrupts obviously won't work well.

So this patch actually is needed to be applied or some other solution have to be provided. Since PCLK rate currently isn't altering anywhere in the kernel, I'd suggest to imply apply this series. Please let me know if you have any objections. I may re-iterate this patch with an extended commit message, describing the resolved problem in a more details, if necessary.