memory: tegra30-emc: Firm up hardware programming sequence

Previously there was a problem where a late handshake handling caused
a memory corruption, this problem was resolved by issuing calibration
command right after changing the timing, but looks like the solution
wasn't entirely correct since calibration interval could be disabled as
well. Now programming sequence is completed immediately after receiving
handshake from CaR, without potentially long delays and in accordance to
the TRM's programming guide.

Secondly, the TRM's programming guide suggests to flush EMC writes by
reading any *MC* register before doing CaR changes. This is also addressed
now.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/memory/tegra/tegra30-emc.c

@@ -332,7 +332,9 @@ struct tegra_emc {
 	struct clk *clk;
 	void __iomem *regs;
 	unsigned int irq;
+	bool bad_state;
 
+	struct emc_timing *new_timing;
 	struct emc_timing *timings;
 	unsigned int num_timings;
 
@@ -346,7 +348,6 @@ struct tegra_emc {
 	bool vref_cal_toggle : 1;
 	bool zcal_long : 1;
 	bool dll_on : 1;
-	bool bad_state : 1;
 
 	struct {
 		struct dentry *root;
@@ -355,6 +356,66 @@ struct tegra_emc {
 	} debugfs;
 };
 
+static int emc_seq_update_timing(struct tegra_emc *emc)
+{
+	u32 val;
+	int err;
+
+	writel_relaxed(EMC_TIMING_UPDATE, emc->regs + EMC_TIMING_CONTROL);
+
+	err = readl_relaxed_poll_timeout_atomic(emc->regs + EMC_STATUS, val,
+				!(val & EMC_STATUS_TIMING_UPDATE_STALLED),
+				1, 200);
+	if (err) {
+		dev_err(emc->dev, "failed to update timing: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+static void emc_complete_clk_change(struct tegra_emc *emc)
+{
+	struct emc_timing *timing = emc->new_timing;
+	unsigned int dram_num;
+	bool failed = false;
+	int err;
+
+	/* re-enable auto-refresh */
+	dram_num = tegra_mc_get_emem_device_count(emc->mc);
+	writel_relaxed(EMC_REFCTRL_ENABLE_ALL(dram_num),
+		       emc->regs + EMC_REFCTRL);
+
+	/* restore auto-calibration */
+	if (emc->vref_cal_toggle)
+		writel_relaxed(timing->emc_auto_cal_interval,
+			       emc->regs + EMC_AUTO_CAL_INTERVAL);
+
+	/* restore dynamic self-refresh */
+	if (timing->emc_cfg_dyn_self_ref) {
+		emc->emc_cfg |= EMC_CFG_DYN_SREF_ENABLE;
+		writel_relaxed(emc->emc_cfg, emc->regs + EMC_CFG);
+	}
+
+	/* set number of clocks to wait after each ZQ command */
+	if (emc->zcal_long)
+		writel_relaxed(timing->emc_zcal_cnt_long,
+			       emc->regs + EMC_ZCAL_WAIT_CNT);
+
+	/* wait for writes to settle */
+	udelay(2);
+
+	/* update restored timing */
+	err = emc_seq_update_timing(emc);
+	if (err)
+		failed = true;
+
+	/* restore early ACK */
+	mc_writel(emc->mc, emc->mc_override, MC_EMEM_ARB_OVERRIDE);
+
+	WRITE_ONCE(emc->bad_state, failed);
+}
+
 static irqreturn_t tegra_emc_isr(int irq, void *data)
 {
 	struct tegra_emc *emc = data;
@@ -365,10 +426,6 @@ static irqreturn_t tegra_emc_isr(int irq, void *data)
 	if (!status)
 		return IRQ_NONE;
 
-	/* notify about EMC-CAR handshake completion */
-	if (status & EMC_CLKCHANGE_COMPLETE_INT)
-		complete(&emc->clk_handshake_complete);
-
 	/* notify about HW problem */
 	if (status & EMC_REFRESH_OVERFLOW_INT)
 		dev_err_ratelimited(emc->dev,
@@ -377,6 +434,18 @@ static irqreturn_t tegra_emc_isr(int irq, void *data)
 	/* clear interrupts */
 	writel_relaxed(status, emc->regs + EMC_INTSTATUS);
 
+	/* notify about EMC-CAR handshake completion */
+	if (status & EMC_CLKCHANGE_COMPLETE_INT) {
+		if (completion_done(&emc->clk_handshake_complete)) {
+			dev_err_ratelimited(emc->dev,
+					    "bogus handshake interrupt\n");
+			return IRQ_NONE;
+		}
+
+		emc_complete_clk_change(emc);
+		complete(&emc->clk_handshake_complete);
+	}
+
 	return IRQ_HANDLED;
 }
 
@@ -444,24 +513,6 @@ static bool emc_dqs_preset(struct tegra_emc *emc, struct emc_timing *timing,
 	return preset;
 }
 
-static int emc_seq_update_timing(struct tegra_emc *emc)
-{
-	u32 val;
-	int err;
-
-	writel_relaxed(EMC_TIMING_UPDATE, emc->regs + EMC_TIMING_CONTROL);
-
-	err = readl_relaxed_poll_timeout_atomic(emc->regs + EMC_STATUS, val,
-				!(val & EMC_STATUS_TIMING_UPDATE_STALLED),
-				1, 200);
-	if (err) {
-		dev_err(emc->dev, "failed to update timing: %d\n", err);
-		return err;
-	}
-
-	return 0;
-}
-
 static int emc_prepare_mc_clk_cfg(struct tegra_emc *emc, unsigned long rate)
 {
 	struct tegra_mc *mc = emc->mc;
@@ -627,9 +678,6 @@ static int emc_prepare_timing_change(struct tegra_emc *emc, unsigned long rate)
 		writel_relaxed(val, emc->regs + EMC_MRS_WAIT_CNT);
 	}
 
-	/* disable interrupt since read access is prohibited after stalling */
-	disable_irq(emc->irq);
-
 	/* this read also completes the writes */
 	val = readl_relaxed(emc->regs + EMC_SEL_DPD_CTRL);
 
@@ -745,17 +793,18 @@ static int emc_prepare_timing_change(struct tegra_emc *emc, unsigned long rate)
 				       emc->regs + EMC_ZQ_CAL);
 	}
 
-	/* re-enable auto-refresh */
-	writel_relaxed(EMC_REFCTRL_ENABLE_ALL(dram_num),
-		       emc->regs + EMC_REFCTRL);
-
 	/* flow control marker 3 */
 	writel_relaxed(0x1, emc->regs + EMC_UNSTALL_RW_AFTER_CLKCHANGE);
 
+	/*
+	 * Read and discard an arbitrary MC register (Note: EMC registers
+	 * can't be used) to ensure the register writes are completed.
+	 */
+	mc_readl(emc->mc, MC_EMEM_ARB_OVERRIDE);
+
 	reinit_completion(&emc->clk_handshake_complete);
 
-	/* interrupt can be re-enabled now */
-	enable_irq(emc->irq);
+	emc->new_timing = timing;
 
 	return 0;
 }
@@ -763,9 +812,7 @@ static int emc_prepare_timing_change(struct tegra_emc *emc, unsigned long rate)
 static int emc_complete_timing_change(struct tegra_emc *emc,
 				      unsigned long rate)
 {
-	struct emc_timing *timing = emc_find_timing(emc, rate);
 	unsigned long timeout;
-	int err;
 
 	timeout = wait_for_completion_timeout(&emc->clk_handshake_complete,
 					      msecs_to_jiffies(100));
@@ -774,33 +821,8 @@ static int emc_complete_timing_change(struct tegra_emc *emc,
 		return -EIO;
 	}
 
-	/* restore auto-calibration */
-	if (emc->vref_cal_toggle)
-		writel_relaxed(timing->emc_auto_cal_interval,
-			       emc->regs + EMC_AUTO_CAL_INTERVAL);
-
-	/* restore dynamic self-refresh */
-	if (timing->emc_cfg_dyn_self_ref) {
-		emc->emc_cfg |= EMC_CFG_DYN_SREF_ENABLE;
-		writel_relaxed(emc->emc_cfg, emc->regs + EMC_CFG);
-	}
-
-	/* set number of clocks to wait after each ZQ command */
-	if (emc->zcal_long)
-		writel_relaxed(timing->emc_zcal_cnt_long,
-			       emc->regs + EMC_ZCAL_WAIT_CNT);
-
-	udelay(2);
-	/* update restored timing */
-	err = emc_seq_update_timing(emc);
-
-	/* restore early ACK */
-	mc_writel(emc->mc, emc->mc_override, MC_EMEM_ARB_OVERRIDE);
-
-	if (err)
-		return err;
-
-	emc->bad_state = false;
+	if (READ_ONCE(emc->bad_state))
+		return -EIO;
 
 	return 0;
 }
@@ -826,7 +848,13 @@ static int emc_clk_change_notify(struct notifier_block *nb,
 
 	switch (msg) {
 	case PRE_RATE_CHANGE:
+		/*
+		 * Disable interrupt since read accesses are prohibited after
+		 * stalling.
+		 */
+		disable_irq(emc->irq);
 		err = emc_prepare_timing_change(emc, cnd->new_rate);
+		enable_irq(emc->irq);
 		break;
 
 	case ABORT_RATE_CHANGE: