linux-kernel - [PATCH v2 03/18] clk: qcom: reset: Ensure write completion on reset de/assertion

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Date: Tue, 06 Feb 2024 19:43:36 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Bjorn Andersson <andersson@...nel.org>, 
 Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>
Cc: Marijn Suijten <marijn.suijten@...ainline.org>, 
 linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Bryan O'Donoghue <bryan.odonoghue@...aro.org>, 
 Dikshita Agarwal <quic_dikshita@...cinc.com>, 
 Vikash Garodia <quic_vgarodia@...cinc.com>, 
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
 Konrad Dybcio <konrad.dybcio@...aro.org>
Subject: [PATCH v2 03/18] clk: qcom: reset: Ensure write completion on
 reset de/assertion

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: db1029814f1f ("clk: qcom: reset: Ensure write completion on reset de/assertion")
Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
---
 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 20d1d35aaf22..d96c96a9089f 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