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

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Date: Mon, 08 Jan 2024 13:32:20 +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>, 
 Konrad Dybcio <konrad.dybcio@...aro.org>, 
 Manivannan Sadhasivam <mani@...nel.org>
Subject: [PATCH 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 c4ac4d18829b..57024d1a0524 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, unsigned lo
 	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