clk: tegra: cclk: Add helpers for handling PLLX rate changes

CCLK should be re-parented away from PLLX if PLLX's rate is changing.
The PLLP parent is a common safe CPU parent for all Tegra SoCs, thus
CCLK will be re-parented to PLLP before PLLX rate-change begins and then
switched back to PLLX after the rate-change completion. This patch adds
helper functions which perform CCLK re-parenting, these helpers will be
utilized by further patches.

Acked-by: Peter De Schrijver <[e-mail]>
Tested-by: Peter Geis <[e-mail]>
Tested-by: Marcel Ziswiler <[e-mail]>
Tested-by: Jasper Korten <[e-mail]>
Tested-by: David Heidelberg <[e-mail]>
Tested-by: Nicolas Chauvet <[e-mail]>
Signed-off-by: Dmitry Osipenko <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/clk/tegra/clk-tegra-super-cclk.c

···
 
 #define SUPER_CDIV_ENB		BIT(31)
 
+static struct tegra_clk_super_mux *cclk_super;
+static bool cclk_on_pllx;
+
 static u8 cclk_super_get_parent(struct clk_hw *hw)
 {
 	return tegra_clk_super_ops.get_parent(hw);
···
 	struct clk_init_data init;
 	u32 val;
 
+	if (WARN_ON(cclk_super))
+		return ERR_PTR(-EBUSY);
+
 	super = kzalloc(sizeof(*super), GFP_KERNEL);
 	if (!super)
 		return ERR_PTR(-ENOMEM);
···
 	clk = clk_register(NULL, &super->hw);
 	if (IS_ERR(clk))
 		kfree(super);
+	else
+		cclk_super = super;
 
 	return clk;
+}
+
+int tegra_cclk_pre_pllx_rate_change(void)
+{
+	if (IS_ERR_OR_NULL(cclk_super))
+		return -EINVAL;
+
+	if (cclk_super_get_parent(&cclk_super->hw) == PLLX_INDEX)
+		cclk_on_pllx = true;
+	else
+		cclk_on_pllx = false;
+
+	/*
+	 * CPU needs to be temporarily re-parented away from PLLX if PLLX
+	 * changes its rate. PLLP is a safe parent for CPU on all Tegra SoCs.
+	 */
+	if (cclk_on_pllx)
+		cclk_super_set_parent(&cclk_super->hw, PLLP_INDEX);
+
+	return 0;
+}
+
+void tegra_cclk_post_pllx_rate_change(void)
+{
+	if (cclk_on_pllx)
+		cclk_super_set_parent(&cclk_super->hw, PLLX_INDEX);
 }

drivers/clk/tegra/clk.h

···
 		const char * const *parent_names, u8 num_parents,
 		unsigned long flags, void __iomem *reg, u8 clk_super_flags,
 		spinlock_t *lock);
+int tegra_cclk_pre_pllx_rate_change(void);
+void tegra_cclk_post_pllx_rate_change(void);
 
 /**
  * struct tegra_sdmmc_mux - switch divider with Low Jitter inputs for SDMMC