linux-kernel - [PATCH v2] i2c: spacemit: fix detect issue

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Message-Id: <20251113-fix-k1-detect-failure-v2-1-b02a9a74f65a@linux.spacemit.com>
Date: Thu, 13 Nov 2025 21:21:50 +0800
From: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
To: Andi Shyti <andi.shyti@...nel.org>, Yixun Lan <dlan@...too.org>, 
 Alex Elder <elder@...cstar.com>, 
 Michael Opdenacker <michael.opdenacker@...tcommit.com>, 
 Aurelien Jarno <aurelien@...el32.net>
Cc: Troy Mitchell <troymitchell988@...il.com>, linux-i2c@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
 spacemit@...ts.linux.dev, Troy Mitchell <troy.mitchell@...ux.spacemit.com>
Subject: [PATCH v2] i2c: spacemit: fix detect issue

This commit addresses two issues causing i2c detect to fail.

The identified issues are:

1. Incorrect error handling for BED (Bus Error No ACK/NAK):
   Before this commit, Both ALD (Arbitration Loss Detected) and
   BED returned -EAGAIN.
2. Missing interrupt status clear after initialization in xfer():
   On the K1 SoC, simply fixing the first issue changed the error
   from -EAGAIN to -ETIMEOUT. Through tracing, it was determined that
   this is likely due to MSD (Master Stop Detected) latency issues.

   That means the MSD bit in the ISR may still be set on the next transfer.
   As a result, the controller won't work — we can see from the scope that
   it doesn't issue any signal.
   (This only occurs during rapid consecutive I2C transfers.
   That explains why the issue only shows up with i2cdetect.)

With these two fixes, i2c device detection now functions correctly on the K1 SoC.

Fixes: 5ea558473fa31 ("i2c: spacemit: add support for SpacemiT K1 SoC")
Tested-by: Aurelien Jarno <aurelien@...el32.net>
Signed-off-by: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
---
Changelog in v2:
- handle ALD and BED errors separately in spacemit_i2c_handle_err()
- move clear_int_status() above spacemit_i2c_init()
- move clear_int_status() from xfer() into spacemit_i2c_init()
- Link to v1: https://lore.kernel.org/all/20251103-fix-k1-detect-failure-v1-1-bb07a8d7de7c@linux.spacemit.com/
---
 drivers/i2c/busses/i2c-k1.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
index 6b918770e612e098b8ad17418f420d87c94df166..d42c03ef5db5984ea8e06b3d7eb485b4f899e616 100644
--- a/drivers/i2c/busses/i2c-k1.c
+++ b/drivers/i2c/busses/i2c-k1.c
@@ -158,11 +158,16 @@ static int spacemit_i2c_handle_err(struct spacemit_i2c_dev *i2c)
 {
 	dev_dbg(i2c->dev, "i2c error status: 0x%08x\n", i2c->status);
 
-	if (i2c->status & (SPACEMIT_SR_BED | SPACEMIT_SR_ALD)) {
+	/* Arbitration Loss Detected */
+	if (i2c->status & SPACEMIT_SR_ALD) {
 		spacemit_i2c_reset(i2c);
 		return -EAGAIN;
 	}
 
+	/* Bus Error No ACK/NAK */
+	if (i2c->status & SPACEMIT_SR_BED)
+		spacemit_i2c_reset(i2c);
+
 	return i2c->status & SPACEMIT_SR_ACKNAK ? -ENXIO : -EIO;
 }
 
@@ -224,6 +229,12 @@ static void spacemit_i2c_check_bus_release(struct spacemit_i2c_dev *i2c)
 	}
 }
 
+static inline void
+spacemit_i2c_clear_int_status(struct spacemit_i2c_dev *i2c, u32 mask)
+{
+	writel(mask & SPACEMIT_I2C_INT_STATUS_MASK, i2c->base + SPACEMIT_ISR);
+}
+
 static void spacemit_i2c_init(struct spacemit_i2c_dev *i2c)
 {
 	u32 val;
@@ -267,12 +278,8 @@ static void spacemit_i2c_init(struct spacemit_i2c_dev *i2c)
 	val = readl(i2c->base + SPACEMIT_IRCR);
 	val |= SPACEMIT_RCR_SDA_GLITCH_NOFIX;
 	writel(val, i2c->base + SPACEMIT_IRCR);
-}
 
-static inline void
-spacemit_i2c_clear_int_status(struct spacemit_i2c_dev *i2c, u32 mask)
-{
-	writel(mask & SPACEMIT_I2C_INT_STATUS_MASK, i2c->base + SPACEMIT_ISR);
+	spacemit_i2c_clear_int_status(i2c, SPACEMIT_I2C_INT_STATUS_MASK);
 }
 
 static void spacemit_i2c_start(struct spacemit_i2c_dev *i2c)

---
base-commit: 6fa9041b7177f6771817b95e83f6df17b147c8c6
change-id: 20251113-fix-k1-detect-failure-63483e45168b

Best regards,
-- 
Troy Mitchell <troy.mitchell@...ux.spacemit.com>