diff mbox series

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

Message ID 20241218001618.488946-9-prabhakar.mahadev-lad.rj@bp.renesas.com
State New
Headers show
Series Add support for I2C bus recovery for riic driver | expand

Commit Message

Lad, Prabhakar Dec. 18, 2024, 12:16 a.m. UTC 
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(-)

Comments

Wolfram Sang Dec. 20, 2024, 9:26 p.m. UTC | #1 
On Wed, Dec 18, 2024 at 12:16:17AM +0000, Prabhakar wrote:
> 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>

...

> -	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;

This initialization can go now. err is 0 already.

With that fixed:

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Lad, Prabhakar Dec. 22, 2024, 4:16 a.m. UTC | #2 
Hi Wolfram,

Thank you for the review.

On Fri, Dec 20, 2024 at 9:27 PM Wolfram Sang
<wsa+renesas@sang-engineering.com> wrote:
>
> On Wed, Dec 18, 2024 at 12:16:17AM +0000, Prabhakar wrote:
> > 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>
>
> ...
>
> > -     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;
>
> This initialization can go now. err is 0 already.
>
Agreed, I will fix that in the v3.

> With that fixed:
>
> Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
>

Cheers,
Prabhakar
diff mbox series

Patch

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;