linux-kernel - [PATCH v4 9/9] i2c: riic: Add `riic_bus_barrier()` to check bus availability

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Message-ID: <20250103091900.428729-10-prabhakar.mahadev-lad.rj@bp.renesas.com>
Date: Fri,  3 Jan 2025 09:19:00 +0000
From: Prabhakar <prabhakar.csengg@...il.com>
To: Chris Brandt <chris.brandt@...esas.com>,
	Andi Shyti <andi.shyti@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>
Cc: linux-renesas-soc@...r.kernel.org,
	linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Prabhakar <prabhakar.csengg@...il.com>,
	Biju Das <biju.das.jz@...renesas.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: [PATCH v4 9/9] i2c: riic: Add `riic_bus_barrier()` to check bus availability

From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>

Introduce a new `riic_bus_barrier()` function to verify bus availability
before initiating an I2C transfer. This function enhances the bus
arbitration check by ensuring that the SDA and SCL lines are not held low,
in addition to checking the BBSY flag using `readb_poll_timeout()`.

Previously, only the BBSY flag was checked to determine bus availability.
However, it is possible for the SDA line to remain low even when BBSY = 0.
This new implementation performs an additional check on the SDA and SCL
lines to avoid potential bus contention issues.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
Reviewed-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
Tested-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
---
v3->v4
- Propogated error code when readb_poll_timeout() failed
- I've kept the RB/TB tags as the changes were minimal.

v2->v3
- Collected RB and tested tags

v1->v2
- Used single register read to check SDA/SCL lines
---
 drivers/i2c/busses/i2c-riic.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-riic.c b/drivers/i2c/busses/i2c-riic.c
index 042933a2a985..bb8383d53b52 100644
--- a/drivers/i2c/busses/i2c-riic.c
+++ b/drivers/i2c/busses/i2c-riic.c
@@ -41,6 +41,7 @@
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -52,6 +53,8 @@
 #define ICCR1_ICE	BIT(7)
 #define ICCR1_IICRST	BIT(6)
 #define ICCR1_SOWP	BIT(4)
+#define ICCR1_SCLI	BIT(1)
+#define ICCR1_SDAI	BIT(0)
 
 #define ICCR2_BBSY	BIT(7)
 #define ICCR2_SP	BIT(3)
@@ -137,6 +140,27 @@ static inline void riic_clear_set_bit(struct riic_dev *riic, u8 clear, u8 set, u
 	riic_writeb(riic, (riic_readb(riic, reg) & ~clear) | set, reg);
 }
 
+static int riic_bus_barrier(struct riic_dev *riic)
+{
+	int ret;
+	u8 val;
+
+	/*
+	 * The SDA line can still be low even when BBSY = 0. Therefore, after checking
+	 * the BBSY flag, also verify that the SDA and SCL lines are not being held low.
+	 */
+	ret = readb_poll_timeout(riic->base + riic->info->regs[RIIC_ICCR2], val,
+				 !(val & ICCR2_BBSY), 10, riic->adapter.timeout);
+	if (ret)
+		return ret;
+
+	if ((riic_readb(riic, RIIC_ICCR1) & (ICCR1_SDAI | ICCR1_SCLI)) !=
+	     (ICCR1_SDAI | ICCR1_SCLI))
+		return -EBUSY;
+
+	return 0;
+}
+
 static int riic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 {
 	struct riic_dev *riic = i2c_get_adapdata(adap);
@@ -149,13 +173,11 @@ static int riic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
 	if (ret)
 		return ret;
 
-	if (riic_readb(riic, RIIC_ICCR2) & ICCR2_BBSY) {
-		riic->err = -EBUSY;
+	riic->err = riic_bus_barrier(riic);
+	if (riic->err)
 		goto out;
-	}
 
 	reinit_completion(&riic->msg_done);
-	riic->err = 0;
 
 	riic_writeb(riic, 0, RIIC_ICSR2);
 
-- 
2.43.0