From 5578d0a79b6430fa1543640dd6f2d397d0886ce7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Beh=C3=BAn?= <kabel@kernel.org>
Date: Sun, 21 May 2023 14:19:40 +0200
Subject: [PATCH] i2c: mv64xxx: Fix reading invalid status value in atomic mode
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Git-commit: 5578d0a79b6430fa1543640dd6f2d397d0886ce7
Patch-mainline: v6.4-rc6
References: git-fixes
There seems to be a bug within the mv64xxx I2C controller, wherein the
status register may not necessarily contain valid value immediately
after the IFLG flag is set in the control register.
My theory is that the controller:
- first sets the IFLG in control register
- then updates the status register
- then raises an interrupt
This may sometime cause weird bugs when in atomic mode, since in this
mode we do not wait for an interrupt, but instead we poll the control
register for IFLG and read status register immediately after.
I encountered -ENXIO from mv64xxx_i2c_fsm() due to this issue when using
this driver in atomic mode.
Note that I've only seen this issue on Armada 385, I don't know whether
other SOCs with this controller are also affected. Also note that this
fix has been in U-Boot for over 4 years [1] without anybody complaining,
so it should not cause regressions.
[1] https://source.denx.de/u-boot/u-boot/-/commit/d50e29662f78
Fixes: 544a8d75f3d6 ("i2c: mv64xxx: Add atomic_xfer method to driver")
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/i2c/busses/i2c-mv64xxx.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
index 047dfef7a657..878c076ebdc6 100644
--- a/drivers/i2c/busses/i2c-mv64xxx.c
+++ b/drivers/i2c/busses/i2c-mv64xxx.c
@@ -520,6 +520,17 @@ mv64xxx_i2c_intr(int irq, void *dev_id)
while (readl(drv_data->reg_base + drv_data->reg_offsets.control) &
MV64XXX_I2C_REG_CONTROL_IFLG) {
+ /*
+ * It seems that sometime the controller updates the status
+ * register only after it asserts IFLG in control register.
+ * This may result in weird bugs when in atomic mode. A delay
+ * of 100 ns before reading the status register solves this
+ * issue. This bug does not seem to appear when using
+ * interrupts.
+ */
+ if (drv_data->atomic)
+ ndelay(100);
+
status = readl(drv_data->reg_base + drv_data->reg_offsets.status);
mv64xxx_i2c_fsm(drv_data, status);
mv64xxx_i2c_do_action(drv_data);
--
2.35.3