net: pcs: rzn1-miic: Add per-SoC control for MIIC register unlock/lock

Make MIIC accessory register unlock/lock behaviour selectable via SoC/OF
data. Add init_unlock_lock_regs and miic_write to struct miic_of_data so
the driver can either perform the traditional global unlock sequence (as
used on RZ/N1) or use a different policy for other SoCs (for example
RZ/T2H, which does not require leaving registers unlocked).

miic_reg_writel() now calls the per-SoC miic_write callback to perform
register writes. Provide miic_reg_writel_unlocked() as the default writer
and set it for the RZ/N1 OF data so existing platforms keep the same
behaviour. Add a miic_unlock_regs() helper that implements the accessory
register unlock sequence so the unlock/lock sequence can be reused where
needed (for example when a SoC requires explicit unlock/lock around
individual accesses).

This change is preparatory work for supporting RZ/T2H.

Signed-off-by: Lad Prabhakar <[e-mail]>
Tested-by: Wolfram Sang <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/pcs/pcs-rzn1-miic.c

···
  * @sw_mode_mask: Switch mode mask
  * @reset_ids: Reset names array
  * @reset_count: Number of entries in the reset_ids array
+ * @init_unlock_lock_regs: Flag to indicate if registers need to be unlocked
+ *  before access.
+ * @miic_write: Function pointer to write a value to a MIIC register
  */
 struct miic_of_data {
 	struct modctrl_match *match_table;
···
 	u8 sw_mode_mask;
 	const char * const *reset_ids;
 	u8 reset_count;
+	bool init_unlock_lock_regs;
+	void (*miic_write)(struct miic *miic, int offset, u32 value);
 };
 
 /**
···
 	return container_of(pcs, struct miic_port, pcs);
 }
 
-static void miic_reg_writel(struct miic *miic, int offset, u32 value)
+static void miic_unlock_regs(struct miic *miic)
+{
+	/* Unprotect register writes */
+	writel(0x00A5, miic->base + MIIC_PRCMD);
+	writel(0x0001, miic->base + MIIC_PRCMD);
+	writel(0xFFFE, miic->base + MIIC_PRCMD);
+	writel(0x0001, miic->base + MIIC_PRCMD);
+}
+
+static void miic_reg_writel_unlocked(struct miic *miic, int offset, u32 value)
 {
 	writel(value, miic->base + offset);
+}
+
+static void miic_reg_writel(struct miic *miic, int offset, u32 value)
+{
+	miic->of_data->miic_write(miic, offset, value);
 }
 
 static u32 miic_reg_readl(struct miic *miic, int offset)
···
 	 * is going to be used in conjunction with the Cortex-M3, this sequence
 	 * will have to be moved in register write
 	 */
-	miic_reg_writel(miic, MIIC_PRCMD, 0x00A5);
-	miic_reg_writel(miic, MIIC_PRCMD, 0x0001);
-	miic_reg_writel(miic, MIIC_PRCMD, 0xFFFE);
-	miic_reg_writel(miic, MIIC_PRCMD, 0x0001);
+	if (miic->of_data->init_unlock_lock_regs)
+		miic_unlock_regs(miic);
 
 	/* TODO: Replace with FIELD_PREP() when compile-time constant
 	 * restriction is lifted. Currently __ffs() returns 0 for sw_mode_mask.
···
 	.miic_port_start = 1,
 	.miic_port_max = 5,
 	.sw_mode_mask = GENMASK(4, 0),
+	.init_unlock_lock_regs = true,
+	.miic_write = miic_reg_writel_unlocked,
 };
 
 static const struct of_device_id miic_of_mtable[] = {