[PATCH net v2 1/4] net: pcs: xpcs-plat: fix runtime PM initialization

[Coia Prant]

The driver calls pm_runtime_set_active() before runtime PM is enabled and
before the CSR clock is prepared and enabled. If the device is later
suspended (e.g. during unbind), the runtime suspend callback tries to
disable a clock that was never enabled, producing:

    clk_csr already disabled
    clk_csr already unprepared

Set the initial runtime PM status to suspended instead, and register a
devm action that force-suspends the device on teardown. Without that
action the CSR clock would stay enabled if the driver is removed while
runtime-active, since nothing triggers a runtime suspend on unbind.
pm_runtime_force_suspend() is not checked because the runtime suspend
callback cannot fail.

The clock is enabled on the first runtime resume (e.g. during MDIO
access).

No upstream platform currently enables this driver with a real CSR clock
dependency, so the issue is not reachable in mainline today. It was
found while using this driver as a reference for the Rockchip XPCS glue
driver.

Signed-off-by: Coia Prant <coiaprant@xxxxxxxxx>
---
 drivers/net/pcs/pcs-xpcs-plat.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/net/pcs/pcs-xpcs-plat.c b/drivers/net/pcs/pcs-xpcs-plat.c
index e669a7b248ac..11c4239bfd74 100644
--- a/drivers/net/pcs/pcs-xpcs-plat.c
+++ b/drivers/net/pcs/pcs-xpcs-plat.c
@@ -275,6 +275,14 @@ static int xpcs_plat_init_res(struct dw_xpcs_plat *pxpcs)
 	return 0;
 }
 
+static void xpcs_plat_exit_clk(void *data)
+{
+	struct dw_xpcs_plat *pxpcs = data;
+	struct device *dev = &pxpcs->pdev->dev;
+
+	pm_runtime_force_suspend(dev);
+}
+
 static int xpcs_plat_init_clk(struct dw_xpcs_plat *pxpcs)
 {
 	struct device *dev = &pxpcs->pdev->dev;
@@ -285,10 +293,12 @@ static int xpcs_plat_init_clk(struct dw_xpcs_plat *pxpcs)
 		return dev_err_probe(dev, PTR_ERR(pxpcs->cclk),
 				     "Failed to get CSR clock\n");
 
-	pm_runtime_set_active(dev);
-	ret = devm_pm_runtime_enable(dev);
+	pm_runtime_set_suspended(dev);
+	pm_runtime_enable(dev);
+
+	ret = devm_add_action_or_reset(dev, xpcs_plat_exit_clk, pxpcs);
 	if (ret) {
-		dev_err(dev, "Failed to enable runtime-PM\n");
+		dev_err(dev, "Failed to register devm for xpcs_plat_exit_clk: %d\n", ret);
 		return ret;
 	}
 
-- 
2.47.3