[PATCH v4 2/2] clk: ingenic-tcu: Fix missing TCU clock for X1000 SoCs

[Aidan MacDonald <aidanmacdonald.0x0@gmail.com>]

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 | 38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/drivers/clk/ingenic/tcu.c b/drivers/clk/ingenic/tcu.c
index 77acfbeb4830..ce8c768db997 100644
--- a/drivers/clk/ingenic/tcu.c
+++ b/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);
-- 
2.35.1