[PATCH] drm/bridge: adv7511: Fix cec clock EPROBE_DEFER handling

[Vincent Whitchurch]

If adv7511's devm_clk_get() for the cec clock returns -EPROBE_DEFER, we
end up in an infinite probe loop.  This happens:

 (1) adv7511's probe is called.

 (2) adv7511's probe adds some secondary i2c devices which bind to the
 dummy driver and thus call driver_deferred_probe_trigger() and
 increment deferred_trigger_count (see driver_bound()).

 (3) adv7511's probe returns -EPROBE_DEFER, and since the
 deferred_trigger_count has changed during the probe call,
 driver_deferred_probe_trigger() is called immediately (see
 really_probe()) and adv7511's probe is scheduled.

 (4) Goto step 1.

[   61.972915] really_probe: bus: 'i2c': really_probe: probing driver adv7511 with device 0-0039
[   61.992734] really_probe: bus: 'i2c': really_probe: probing driver dummy with device 0-003f
[   61.993343] driver_bound: driver: 'dummy': driver_bound: bound to device '0-003f'
[   61.993626] really_probe: bus: 'i2c': really_probe: bound device 0-003f to driver dummy
[   61.995604] really_probe: bus: 'i2c': really_probe: probing driver dummy with device 0-0038
[   61.996381] driver_bound: driver: 'dummy': driver_bound: bound to device '0-0038'
[   61.996663] really_probe: bus: 'i2c': really_probe: bound device 0-0038 to driver dummy
[   61.998651] really_probe: bus: 'i2c': really_probe: probing driver dummy with device 0-003c
[   61.999222] driver_bound: driver: 'dummy': driver_bound: bound to device '0-003c'
[   61.999496] really_probe: bus: 'i2c': really_probe: bound device 0-003c to driver dummy
[   62.010050] really_probe: i2c 0-0039: Driver adv7511 requests probe deferral
[   62.011380] really_probe: bus: 'platform': really_probe: probing driver pwm-clock with device clock-cec
[   62.012812] really_probe: platform clock-cec: Driver pwm-clock requests probe deferral
[   62.024679] really_probe: bus: 'i2c': really_probe: probing driver adv7511 with device 0-0039

Fix this by calling devm_clk_get() before registering the secondary
devices.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch at axis.com>
---
 drivers/gpu/drm/bridge/adv7511/adv7511_cec.c | 30 +++++++-------------
 drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 11 +++++--
 2 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_cec.c b/drivers/gpu/drm/bridge/adv7511/adv7511_cec.c
index a20a45c0b353..4b0fee32be21 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7511_cec.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7511_cec.c
@@ -286,28 +286,17 @@ static const struct cec_adap_ops adv7511_cec_adap_ops = {
 	.adap_transmit = adv7511_cec_adap_transmit,
 };
 
-static int adv7511_cec_parse_dt(struct device *dev, struct adv7511 *adv7511)
-{
-	adv7511->cec_clk = devm_clk_get(dev, "cec");
-	if (IS_ERR(adv7511->cec_clk)) {
-		int ret = PTR_ERR(adv7511->cec_clk);
-
-		adv7511->cec_clk = NULL;
-		return ret;
-	}
-	clk_prepare_enable(adv7511->cec_clk);
-	adv7511->cec_clk_freq = clk_get_rate(adv7511->cec_clk);
-	return 0;
-}
-
 int adv7511_cec_init(struct device *dev, struct adv7511 *adv7511)
 {
 	unsigned int offset = adv7511->type == ADV7533 ?
 						ADV7533_REG_CEC_OFFSET : 0;
-	int ret = adv7511_cec_parse_dt(dev, adv7511);
+	int ret;
 
-	if (ret)
-		goto err_cec_parse_dt;
+	if (!adv7511->cec_clk)
+		goto err_cec_no_clock;
+
+	clk_prepare_enable(adv7511->cec_clk);
+	adv7511->cec_clk_freq = clk_get_rate(adv7511->cec_clk);
 
 	adv7511->cec_adap = cec_allocate_adapter(&adv7511_cec_adap_ops,
 		adv7511, dev_name(dev), CEC_CAP_DEFAULTS, ADV7511_MAX_ADDRS);
@@ -342,8 +331,11 @@ int adv7511_cec_init(struct device *dev, struct adv7511 *adv7511)
 err_cec_alloc:
 	dev_info(dev, "Initializing CEC failed with error %d, disabling CEC\n",
 		 ret);
-err_cec_parse_dt:
+	clk_disable_unprepare(adv7511->cec_clk);
+	/* Ensure that adv7511_remove() doesn't attempt to disable it again. */
+	adv7511->cec_clk = NULL;
+err_cec_no_clock:
 	regmap_write(adv7511->regmap, ADV7511_REG_CEC_CTRL + offset,
 		     ADV7511_CEC_CTRL_POWER_DOWN);
-	return ret == -EPROBE_DEFER ? ret : 0;
+	return 0;
 }
diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
index 9e13e466e72c..ebc548e23ece 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
@@ -1122,6 +1122,15 @@ static int adv7511_probe(struct i2c_client *i2c, const struct i2c_device_id *id)
 	if (ret)
 		return ret;
 
+	adv7511->cec_clk = devm_clk_get(dev, "cec");
+	if (IS_ERR(adv7511->cec_clk)) {
+		ret = PTR_ERR(adv7511->cec_clk);
+		if (ret == -EPROBE_DEFER)
+			return ret;
+
+		adv7511->cec_clk = NULL;
+	}
+
 	ret = adv7511_init_regulators(adv7511);
 	if (ret) {
 		dev_err(dev, "failed to init regulators\n");
@@ -1226,8 +1235,6 @@ static int adv7511_probe(struct i2c_client *i2c, const struct i2c_device_id *id)
 
 err_unregister_cec:
 	i2c_unregister_device(adv7511->i2c_cec);
-	if (adv7511->cec_clk)
-		clk_disable_unprepare(adv7511->cec_clk);
 err_i2c_unregister_packet:
 	i2c_unregister_device(adv7511->i2c_packet);
 err_i2c_unregister_edid:
-- 
2.25.1