clk: ingenic-tcu: Fix missing TCU clock for X1000 SoCs

The TCU clock gate on X1000 wasn't requested by the driver and could
be gated automatically later on in boot, which prevents timers from
running and breaks PWM.

Add a workaround to support old device trees that don't specify the
"tcu" clock gate. In this case the kernel will print a warning and
attempt to continue without the clock, which is wrong, but it could
work if "clk_ignore_unused" is in the kernel arguments.

Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@gmail.com>

drivers/clk/ingenic/tcu.c

@@ -31,6 +31,7 @@ struct ingenic_soc_info {
 	unsigned int num_channels;
 	bool has_ost;
 	bool has_tcu_clk;
+	bool allow_missing_tcu_clk;
 };
 
 struct ingenic_tcu_clk_info {
@@ -320,7 +321,8 @@ static const struct ingenic_soc_info jz4770_soc_info = {
 static const struct ingenic_soc_info x1000_soc_info = {
 	.num_channels = 8,
 	.has_ost = false, /* X1000 has OST, but it not belong TCU */
-	.has_tcu_clk = false,
+	.has_tcu_clk = true,
+	.allow_missing_tcu_clk = true,
 };
 
 static const struct of_device_id __maybe_unused ingenic_tcu_of_match[] __initconst = {
@@ -354,15 +356,27 @@ static int __init ingenic_tcu_probe(struct device_node *np)
 	if (tcu->soc_info->has_tcu_clk) {
 		tcu->clk = of_clk_get_by_name(np, "tcu");
 		if (IS_ERR(tcu->clk)) {
-			ret = PTR_ERR(tcu->clk);
-			pr_crit("Cannot get TCU clock\n");
-			goto err_free_tcu;
-		}
-
-		ret = clk_prepare_enable(tcu->clk);
-		if (ret) {
-			pr_crit("Unable to enable TCU clock\n");
-			goto err_put_clk;
+			/*
+			 * Old device trees for some SoCs did not include the
+			 * TCU clock because this driver (incorrectly) didn't
+			 * use it. In this case we complain loudly and attempt
+			 * to continue without the clock, which might work if
+			 * booting with workarounds like "clk_ignore_unused".
+			 */
+			if (tcu->soc_info->allow_missing_tcu_clk &&
+			    PTR_ERR(tcu->clk) == -EINVAL) {
+				pr_warn("TCU clock missing from device tree, please update your device tree\n");
+				tcu->clk = NULL;
+			} else {
+				pr_crit("Cannot get TCU clock from device tree\n");
+				goto err_free_tcu;
+			}
+		} else {
+			ret = clk_prepare_enable(tcu->clk);
+			if (ret) {
+				pr_crit("Unable to enable TCU clock\n");
+				goto err_put_clk;
+			}
 		}
 	}
 
@@ -432,10 +446,10 @@ static int __init ingenic_tcu_probe(struct device_node *np)
 			clk_hw_unregister(tcu->clocks->hws[i]);
 	kfree(tcu->clocks);
 err_clk_disable:
-	if (tcu->soc_info->has_tcu_clk)
+	if (tcu->clk)
 		clk_disable_unprepare(tcu->clk);
 err_put_clk:
-	if (tcu->soc_info->has_tcu_clk)
+	if (tcu->clk)
 		clk_put(tcu->clk);
 err_free_tcu:
 	kfree(tcu);