memory: tegra30-emc: Firm up suspend/resume sequence

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>
Signed-off-by: Thierry Reding <treding@nvidia.com>

diff --git a/drivers/memory/tegra/tegra30-emc.c b/drivers/memory/tegra/tegra30-emc.c
index d61cb74..b86ae0c 100644 (file)
--- a/drivers/memory/tegra/tegra30-emc.c
+++ b/drivers/memory/tegra/tegra30-emc.c
@@ -346,7 +346,6 @@ struct tegra_emc {
        bool vref_cal_toggle : 1;
        bool zcal_long : 1;
        bool dll_on : 1;
-       bool prepared : 1;
        bool bad_state : 1;
 
        struct {
@@ -758,9 +757,6 @@ 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;
 }
 
@@ -769,13 +765,12 @@ 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;
        }
 
@@ -797,22 +792,23 @@ 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;
@@ -1354,13 +1350,17 @@ unset_cb:
 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;
@@ -1375,6 +1375,8 @@ static int tegra_emc_resume(struct device *dev)
        emc_setup_hw(emc);
        emc->bad_state = false;
 
+       clk_rate_exclusive_put(emc->clk);
+
        return 0;
 }