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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: "Marek Behún" <kabel@kernel.org>,
	"Gregory CLEMENT" <gregory.clement@bootlin.com>,
	"Samuel Holland" <samuel@sholland.org>,
	"Wolfram Sang" <wsa@kernel.org>,
	"Sasha Levin" <sashal@kernel.org>,
	linux-i2c@vger.kernel.org
Subject: [PATCH AUTOSEL 4.9 6/8] i2c: mv64xxx: Fix random system lock caused by runtime PM
Date: Mon, 19 Apr 2021 16:45:52 -0400
Message-ID: <20210419204554.7071-6-sashal@kernel.org> (raw)
In-Reply-To: <20210419204554.7071-1-sashal@kernel.org>

From: Marek Behún <kabel@kernel.org>

[ Upstream commit 39930213e7779b9c4257499972b8afb8858f1a2d ]

I noticed a weird bug with this driver on Marvell CN9130 Customer
Reference Board.

Sometime after boot, the system locks with the following message:
 [104.071363] i2c i2c-0: mv64xxx: I2C bus locked, block: 1, time_left: 0

The system does not respond afterwards, only warns about RCU stalls.

This first appeared with commit e5c02cf54154 ("i2c: mv64xxx: Add runtime
PM support").

With further experimentation I discovered that adding a delay into
mv64xxx_i2c_hw_init() fixes this issue. This function is called before
every xfer, due to how runtime PM works in this driver. It seems that in
order to work correctly, a delay is needed after the bus is reset in
this function.

Since there already is a known erratum with this controller needing a
delay, I assume that this is just another place this needs to be
applied. Therefore I apply the delay only if errata_delay is true.

Signed-off-by: Marek Behún <kabel@kernel.org>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/i2c/busses/i2c-mv64xxx.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
index 5c9dea7a40bc..b10e89b4f8e9 100644
--- a/drivers/i2c/busses/i2c-mv64xxx.c
+++ b/drivers/i2c/busses/i2c-mv64xxx.c
@@ -217,6 +217,10 @@ mv64xxx_i2c_hw_init(struct mv64xxx_i2c_data *drv_data)
 	writel(0, drv_data->reg_base + drv_data->reg_offsets.ext_addr);
 	writel(MV64XXX_I2C_REG_CONTROL_TWSIEN | MV64XXX_I2C_REG_CONTROL_STOP,
 		drv_data->reg_base + drv_data->reg_offsets.control);
+
+	if (drv_data->errata_delay)
+		udelay(5);
+
 	drv_data->state = MV64XXX_I2C_STATE_IDLE;
 }
 
-- 
2.30.2


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