[PATCH v2 2/2] regulator: hi655x: Bump parent pmic module use count

[Jeremy Linton <lintonrjeremy@gmail.com>]

The hi655x-regulator driver depends on the parent pmic/mfc
device driver but doesn't increase its use count. This results
in system crashes if the parent module is unloaded while the
regulators are still in use. Add explicit module get/put
calls to keep the parent from being unloaded.

example crash:

 Unable to handle kernel paging request at virtual address ffff800078fc5c78
 ...
 [<ffff800078fc5c78>] 0xffff800078fc5c78
 [<ffff0000086248f8>] regulator_set_voltage_sel_regmap+0x50/0x98
 [<ffff00000861e830>] _regulator_do_set_voltage+0x4c8/0x7c0
 [<ffff000008620804>] regulator_set_voltage_unlocked+0xc4/0x258
 [<ffff0000086209d4>] regulator_set_voltage+0x3c/0x70
 [<ffff000000af1b30>] mmc_regulator_set_ocr+0x48/0x100 [mmc_core]
 [<ffff000000c93da8>] dw_mci_set_ios+0x1e8/0x280 [dw_mmc]
 [<ffff000000af483c>] mmc_set_initial_state+0x84/0xf8 [mmc_core]
 [<ffff000000af490c>] mmc_power_up.part.13+0x5c/0x1f8 [mmc_core]
 [<ffff000000af5c20>] mmc_rescan+0x270/0x3b0 [mmc_core]
 [<ffff0000080f3a14>] process_one_work+0x264/0x7c0
 [<ffff0000080f3fc4>] worker_thread+0x54/0x430
 [<ffff0000080fc5dc>] kthread+0x104/0x130
 [<ffff000008083380>] ret_from_fork+0x10/0x50

Signed-off-by: Jeremy Linton <lintonrjeremy@gmail.com>
---
 drivers/regulator/hi655x-regulator.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/regulator/hi655x-regulator.c b/drivers/regulator/hi655x-regulator.c
index 36ae54b..336aaed 100644
--- a/drivers/regulator/hi655x-regulator.c
+++ b/drivers/regulator/hi655x-regulator.c
@@ -185,16 +185,29 @@ static int hi655x_regulator_probe(struct platform_device *pdev)
 	struct hi655x_pmic *pmic;
 	struct regulator_config config = { };
 	struct regulator_dev *rdev;
+	struct device *parent = pdev->dev.parent;
 
-	pmic = dev_get_drvdata(pdev->dev.parent);
+	if (!parent) {
+		dev_err(&pdev->dev, "no regulator parent node\n");
+		return -ENODEV;
+	}
+
+	pmic = dev_get_drvdata(parent);
 	if (!pmic) {
 		dev_err(&pdev->dev, "no pmic in the regulator parent node\n");
 		return -ENODEV;
 	}
 
+	if (!try_module_get(parent->driver->owner)) {
+		dev_err(&pdev->dev, "unable to get parent module\n");
+		return -ENODEV;
+	}
+
 	regulator = devm_kzalloc(&pdev->dev, sizeof(*regulator), GFP_KERNEL);
-	if (!regulator)
+	if (!regulator)	{
+		module_put(parent->driver->owner);
 		return -ENOMEM;
+	}
 
 	platform_set_drvdata(pdev, regulator);
 
@@ -214,6 +227,14 @@ static int hi655x_regulator_probe(struct platform_device *pdev)
 	return 0;
 }
 
+static int hi655x_regulator_remove(struct platform_device *pdev)
+{
+	struct device *parent = pdev->dev.parent;
+
+	module_put(parent->driver->owner);
+	return 0;
+}
+
 static const struct platform_device_id hi655x_regulator_table[] = {
 	{ .name = "hi655x-regulator" },
 	{},
@@ -226,6 +247,7 @@ static struct platform_driver hi655x_regulator_driver = {
 		.name	= "hi655x-regulator",
 	},
 	.probe	= hi655x_regulator_probe,
+	.remove = hi655x_regulator_remove
 };
 module_platform_driver(hi655x_regulator_driver);
 
-- 
2.10.2