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Subject[PATCH v2 1/3] memory: tegra30-emc: Firm up suspend/resume sequence
Date
The current code doesn't prevent race conditions of suspend/resume vs CCF.
Let's take exclusive control over the EMC clock during suspend in a way
that is free from race conditions.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
drivers/memory/tegra/tegra30-emc.c | 38 ++++++++++++++++--------------
1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/memory/tegra/tegra30-emc.c b/drivers/memory/tegra/tegra30-emc.c
index 0b6a5e451ea3..770808da957d 100644
--- a/drivers/memory/tegra/tegra30-emc.c
+++ b/drivers/memory/tegra/tegra30-emc.c
@@ -345,7 +345,6 @@ struct tegra_emc {
bool vref_cal_toggle : 1;
bool zcal_long : 1;
bool dll_on : 1;
- bool prepared : 1;
bool bad_state : 1;
};

@@ -751,9 +750,6 @@ static int emc_prepare_timing_change(struct tegra_emc *emc, unsigned long rate)
/* interrupt can be re-enabled now */
enable_irq(emc->irq);

- emc->bad_state = false;
- emc->prepared = true;
-
return 0;
}

@@ -762,13 +758,12 @@ static int emc_complete_timing_change(struct tegra_emc *emc,
{
struct emc_timing *timing = emc_find_timing(emc, rate);
unsigned long timeout;
- int ret;
+ int err;

timeout = wait_for_completion_timeout(&emc->clk_handshake_complete,
msecs_to_jiffies(100));
if (timeout == 0) {
dev_err(emc->dev, "emc-car handshake failed\n");
- emc->bad_state = true;
return -EIO;
}

@@ -790,22 +785,23 @@ static int emc_complete_timing_change(struct tegra_emc *emc,

udelay(2);
/* update restored timing */
- ret = emc_seq_update_timing(emc);
- if (ret)
- emc->bad_state = true;
+ err = emc_seq_update_timing(emc);

/* restore early ACK */
mc_writel(emc->mc, emc->mc_override, MC_EMEM_ARB_OVERRIDE);

- emc->prepared = false;
+ if (err)
+ return err;
+
+ emc->bad_state = false;

- return ret;
+ return 0;
}

static int emc_unprepare_timing_change(struct tegra_emc *emc,
unsigned long rate)
{
- if (emc->prepared && !emc->bad_state) {
+ if (!emc->bad_state) {
/* shouldn't ever happen in practice */
dev_err(emc->dev, "timing configuration can't be reverted\n");
emc->bad_state = true;
@@ -1181,13 +1177,17 @@ static int tegra_emc_probe(struct platform_device *pdev)
static int tegra_emc_suspend(struct device *dev)
{
struct tegra_emc *emc = dev_get_drvdata(dev);
+ int err;
+
+ /* take exclusive control over the clock's rate */
+ err = clk_rate_exclusive_get(emc->clk);
+ if (err) {
+ dev_err(emc->dev, "failed to acquire clk: %d\n", err);
+ return err;
+ }

- /*
- * Suspending in a bad state will hang machine. The "prepared" var
- * shall be always false here unless it's a kernel bug that caused
- * suspending in a wrong order.
- */
- if (WARN_ON(emc->prepared) || emc->bad_state)
+ /* suspending in a bad state will hang machine */
+ if (WARN(emc->bad_state, "hardware in a bad state\n"))
return -EINVAL;

emc->bad_state = true;
@@ -1202,6 +1202,8 @@ static int tegra_emc_resume(struct device *dev)
emc_setup_hw(emc);
emc->bad_state = false;

+ clk_rate_exclusive_put(emc->clk);
+
return 0;
}

--
2.24.0
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