1 files changed, 76 insertions, 2 deletions

diff --git a/drivers/clk/rockchip/clk-mmc-phase.c b/drivers/clk/rockchip/clk-mmc-phase.c
index 077fcdc7908b..026a26bb702d 100644
--- a/drivers/clk/rockchip/clk-mmc-phase.c
+++ b/drivers/clk/rockchip/clk-mmc-phase.c
@@ -25,6 +25,8 @@ struct rockchip_mmc_clock {
 	void __iomem	*reg;
 	int		id;
 	int		shift;
+	int		cached_phase;
+	struct notifier_block clk_rate_change_nb;
 };
 
 #define to_mmc_clock(_hw) container_of(_hw, struct rockchip_mmc_clock, hw)
@@ -58,6 +60,12 @@ static int rockchip_mmc_get_phase(struct clk_hw *hw)
 	u16 degrees;
 	u32 delay_num = 0;
 
+	/* See the comment for rockchip_mmc_set_phase below */
+	if (!rate) {
+		pr_err("%s: invalid clk rate\n", __func__);
+		return -EINVAL;
+	}
+
 	raw_value = readl(mmc_clock->reg) >> (mmc_clock->shift);
 
 	degrees = (raw_value & ROCKCHIP_MMC_DEGREE_MASK) * 90;
@@ -84,6 +92,23 @@ static int rockchip_mmc_set_phase(struct clk_hw *hw, int degrees)
 	u32 raw_value;
 	u32 delay;
 
+	/*
+	 * The below calculation is based on the output clock from
+	 * MMC host to the card, which expects the phase clock inherits
+	 * the clock rate from its parent, namely the output clock
+	 * provider of MMC host. However, things may go wrong if
+	 * (1) It is orphan.
+	 * (2) It is assigned to the wrong parent.
+	 *
+	 * This check help debug the case (1), which seems to be the
+	 * most likely problem we often face and which makes it difficult
+	 * for people to debug unstable mmc tuning results.
+	 */
+	if (!rate) {
+		pr_err("%s: invalid clk rate\n", __func__);
+		return -EINVAL;
+	}
+
 	nineties = degrees / 90;
 	remainder = (degrees % 90);
 
@@ -139,6 +164,41 @@ static const struct clk_ops rockchip_mmc_clk_ops = {
 	.set_phase	= rockchip_mmc_set_phase,
 };
 
+#define to_rockchip_mmc_clock(x) \
+	container_of(x, struct rockchip_mmc_clock, clk_rate_change_nb)
+static int rockchip_mmc_clk_rate_notify(struct notifier_block *nb,
+					unsigned long event, void *data)
+{
+	struct rockchip_mmc_clock *mmc_clock = to_rockchip_mmc_clock(nb);
+	struct clk_notifier_data *ndata = data;
+
+	/*
+	 * rockchip_mmc_clk is mostly used by mmc controllers to sample
+	 * the intput data, which expects the fixed phase after the tuning
+	 * process. However if the clock rate is changed, the phase is stale
+	 * and may break the data sampling. So here we try to restore the phase
+	 * for that case, except that
+	 * (1) cached_phase is invaild since we inevitably cached it when the
+	 * clock provider be reparented from orphan to its real parent in the
+	 * first place. Otherwise we may mess up the initialization of MMC cards
+	 * since we only set the default sample phase and drive phase later on.
+	 * (2) the new coming rate is higher than the older one since mmc driver
+	 * set the max-frequency to match the boards' ability but we can't go
+	 * over the heads of that, otherwise the tests smoke out the issue.
+	 */
+	if (ndata->old_rate <= ndata->new_rate)
+		return NOTIFY_DONE;
+
+	if (event == PRE_RATE_CHANGE)
+		mmc_clock->cached_phase =
+			rockchip_mmc_get_phase(&mmc_clock->hw);
+	else if (mmc_clock->cached_phase != -EINVAL &&
+		 event == POST_RATE_CHANGE)
+		rockchip_mmc_set_phase(&mmc_clock->hw, mmc_clock->cached_phase);
+
+	return NOTIFY_DONE;
+}
+
 struct clk *rockchip_clk_register_mmc(const char *name,
 				const char *const *parent_names, u8 num_parents,
 				void __iomem *reg, int shift)
@@ -146,6 +206,7 @@ struct clk *rockchip_clk_register_mmc(const char *name,
 	struct clk_init_data init;
 	struct rockchip_mmc_clock *mmc_clock;
 	struct clk *clk;
+	int ret;
 
 	mmc_clock = kmalloc(sizeof(*mmc_clock), GFP_KERNEL);
 	if (!mmc_clock)
@@ -162,8 +223,21 @@ struct clk *rockchip_clk_register_mmc(const char *name,
 	mmc_clock->shift = shift;
 
 	clk = clk_register(NULL, &mmc_clock->hw);
-	if (IS_ERR(clk))
-		kfree(mmc_clock);
+	if (IS_ERR(clk)) {
+		ret = PTR_ERR(clk);
+		goto err_register;
+	}
+
+	mmc_clock->clk_rate_change_nb.notifier_call =
+				&rockchip_mmc_clk_rate_notify;
+	ret = clk_notifier_register(clk, &mmc_clock->clk_rate_change_nb);
+	if (ret)
+		goto err_notifier;
 
 	return clk;
+err_notifier:
+	clk_unregister(clk);
+err_register:
+	kfree(mmc_clock);
+	return ERR_PTR(ret);
 }