[PATCH v2 8/9] i2c: riic: Add `riic_bus_barrier()` to check bus availability

Prabhakar
2024-12-18T00:16:41Z

From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.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@bp.renesas.com>
---
v1->v2
- Used single register read to check SDA/SCL lines
---
drivers/i2c/busses/i2c-riic.c | 29 ++++++++++++++++++++++++++---
1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-riic.c b/drivers/i2c/busses/i2c-riic.c
index a2d0cde5ac54..586092454bb2 100644
--- a/drivers/i2c/busses/i2c-riic.c
+++ b/drivers/i2c/busses/i2c-riic.c
@@ -40,6 +40,7 @@
#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>
@@ -50,6 +51,8 @@
#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)
@@ -135,6 +138,27 @@ 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 -EBUSY;
+
+ 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);
@@ -147,10 +171,9 @@ 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;
--
2.43.0