[PATCH 5.15 189/317] clk: qcom: reset: Ensure write completion on reset de/assertion

[Sasha Levin]

From: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>

[ Upstream commit 2f8cf2c3f3e3f7ef61bd19abb4b0bb797ad50aaf ]

Trying to toggle the resets in a rapid fashion can lead to the changes
not actually arriving at the clock controller block when we expect them
to. This was observed at least on SM8250.

Read back the value after regmap_update_bits to ensure write completion.

Fixes: b36ba30c8ac6 ("clk: qcom: Add reset controller support")
Signed-off-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240105-topic-venus_reset-v2-3-c37eba13b5ce@xxxxxxxxxx
Signed-off-by: Bjorn Andersson <andersson@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/clk/qcom/reset.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/qcom/reset.c b/drivers/clk/qcom/reset.c
index 20d1d35aaf229..d96c96a9089f4 100644
--- a/drivers/clk/qcom/reset.c
+++ b/drivers/clk/qcom/reset.c
@@ -33,7 +33,12 @@ static int qcom_reset_set_assert(struct reset_controller_dev *rcdev,
 	map = &rst->reset_map[id];
 	mask = map->bitmask ? map->bitmask : BIT(map->bit);
 
-	return regmap_update_bits(rst->regmap, map->reg, mask, assert ? mask : 0);
+	regmap_update_bits(rst->regmap, map->reg, mask, assert ? mask : 0);
+
+	/* Read back the register to ensure write completion, ignore the value */
+	regmap_read(rst->regmap, map->reg, &mask);
+
+	return 0;
 }
 
 static int qcom_reset_assert(struct reset_controller_dev *rcdev, unsigned long id)
-- 
2.43.0