[PATCH] clk: keystone: sci-clk: Handle missing get_num_parents operation

[Beleswar Padhi]

The sci-clk driver unconditionally calls the get_num_parents TI-SCI
operation while scanning clocks, both from DT and from firmware. This
works for all cases today, but with future support for some System
Controllers (e.g. PDM on TDA54), this may not be always right.

The PDM system controller on TI TDA54 SoC manages clock parents
internally and does not support the clock parent related ops. Therefore,
when scanning clocks from DT, treat the clock as having a single parent
if get_num_parents is not provided. Such a clock is registered without
parents, so the get_parent and set_parent operations are never invoked
for it.

Scanning clocks from firmware relies on get_num_parents to discover the
valid clock IDs, so return -EOPNOTSUPP in that case instead.

Signed-off-by: Beleswar Padhi <b-padhi@xxxxxx>
---
Testing Done:
 - Boot test on all keystone and K3 platforms.
 - Verified that the patch does not result in any warnings or errors

Logs:
https://gist.github.com/3V3RYONE/d821cea46f5dc1e70a759c97878fa487

Note:
This patch is independent and can be applied directly.

 drivers/clk/keystone/sci-clk.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/keystone/sci-clk.c b/drivers/clk/keystone/sci-clk.c
index 9d2094bd48e3b..5bf615893a8c0 100644
--- a/drivers/clk/keystone/sci-clk.c
+++ b/drivers/clk/keystone/sci-clk.c
@@ -468,6 +468,13 @@ static int ti_sci_scan_clocks_from_fw(struct sci_clk_provider *provider)
 	int gap_size = 0;
 	struct device *dev = provider->dev;
 
+	/*
+	 * Clocks are discovered by probing the firmware with get_num_parents,
+	 * which is not available with every system firmware (e.g. ABI5.0 PDM).
+	 */
+	if (!provider->ops->get_num_parents)
+		return -EOPNOTSUPP;
+
 	while (1) {
 		ret = provider->ops->get_num_parents(provider->sci, dev_id,
 						     clk_id,
@@ -589,10 +596,18 @@ static int ti_sci_scan_clocks_from_dt(struct sci_clk_provider *provider)
 				sci_clk->dev_id = args.args[0];
 				sci_clk->clk_id = args.args[1];
 				sci_clk->provider = provider;
-				provider->ops->get_num_parents(provider->sci,
-							       sci_clk->dev_id,
-							       sci_clk->clk_id,
-							       (void *)&sci_clk->num_parents);
+				/*
+				 * Firmware without get_num_parents (e.g. ABI5.0
+				 * PDM) manages clock parents internally, so
+				 * treat the clock as having a single parent.
+				 */
+				if (provider->ops->get_num_parents)
+					provider->ops->get_num_parents(provider->sci,
+								       sci_clk->dev_id,
+								       sci_clk->clk_id,
+								       &sci_clk->num_parents);
+				else
+					sci_clk->num_parents = 1;
 				list_add_tail(&sci_clk->node, &clks);
 
 				num_clks++;
-- 
2.34.1