[PATCH 0/2] i2c: recovery: add bus_free callback

[PATCH 0/2] i2c: recovery: add bus_free callback

[Wolfram Sang]

Add a new callback for IP cores which cannot report SDA directly but only a
'bus free' state. Implement this for the Renesas R-Car driver.

It has been tested with a Renesas Lager board (R-Car H2).

A branch (with further improvements) can be found here:

git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/i2c/recovery/write-byte-fix

Looking forward to comments.

Kind regards,

   Wolfram

Wolfram Sang (2):
  i2c: recovery: add get_bus_free callback
  i2c: rcar: use the new get_bus_free callback

 drivers/i2c/busses/i2c-rcar.c | 21 +++++++++++----------
 drivers/i2c/i2c-core-base.c   | 27 +++++++++++++++++++++++----
 include/linux/i2c.h           |  3 +++
 3 files changed, 37 insertions(+), 14 deletions(-)

-- 
2.11.0

[PATCH 1/2] i2c: recovery: add get_bus_free callback

[Wolfram Sang]

Some IP cores have an internal 'bus free' logic which may be more
advanced than just checking if SDA is high. Add a separate callback to
get this status. Filling it is optional.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/i2c/i2c-core-base.c | 27 +++++++++++++++++++++++----
 include/linux/i2c.h         |  3 +++
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index c7995efd58ea..59f8dfc5be36 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -158,6 +158,22 @@ static void set_sda_gpio_value(struct i2c_adapter *adap, int val)
 	gpiod_set_value_cansleep(adap->bus_recovery_info->sda_gpiod, val);
 }
 
+static int i2c_generic_bus_free(struct i2c_adapter *adap)
+{
+	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
+	int ret = -EOPNOTSUPP;
+
+	if (bri->get_bus_free)
+		ret = bri->get_bus_free(adap);
+	else if (bri->get_sda)
+		ret = bri->get_sda(adap);
+
+	if (ret < 0)
+		return ret;
+
+	return ret ? 0 : -EBUSY;
+}
+
 /*
  * We are generating clock pulses. ndelay() determines durating of clk pulses.
  * We will generate clock with rate 100 KHz and so duration of both clock levels
@@ -169,7 +185,7 @@ static void set_sda_gpio_value(struct i2c_adapter *adap, int val)
 int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 {
 	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
-	int i = 0, val = 1, ret = 0;
+	int i = 0, val = 1, ret;
 
 	if (bri->prepare_recovery)
 		bri->prepare_recovery(adap);
@@ -207,14 +223,17 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 			bri->set_sda(adap, val);
 		ndelay(RECOVERY_NDELAY / 2);
 
-		/* Break if SDA is high */
-		if (val && bri->get_sda) {
-			ret = bri->get_sda(adap) ? 0 : -EBUSY;
+		if (val) {
+			ret = i2c_generic_bus_free(adap);
 			if (ret == 0)
 				break;
 		}
 	}
 
+	/* If we can't check bus status, assume recovery worked */
+	if (ret == -EOPNOTSUPP)
+		ret = 0;
+
 	if (bri->unprepare_recovery)
 		bri->unprepare_recovery(adap);
 
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 9d1818c56775..60e224428a85 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -587,6 +587,8 @@ struct i2c_timings {
  * @set_sda: This sets/clears the SDA line. This or get_sda() is mandatory for
  *	generic SCL recovery. Populated internally, if sda_gpio is a valid GPIO,
  *	for generic GPIO recovery.
+ * @get_bus_free: Returns the bus free state as seen from the IP core in case it
+ *	has a more complex internal logic than just reading SDA. Optional.
  * @prepare_recovery: This will be called before starting recovery. Platform may
  *	configure padmux here for SDA/SCL line or something else they want.
  * @unprepare_recovery: This will be called after completing recovery. Platform
@@ -601,6 +603,7 @@ struct i2c_bus_recovery_info {
 	void (*set_scl)(struct i2c_adapter *adap, int val);
 	int (*get_sda)(struct i2c_adapter *adap);
 	void (*set_sda)(struct i2c_adapter *adap, int val);
+	int (*get_bus_free)(struct i2c_adapter *adap);
 
 	void (*prepare_recovery)(struct i2c_adapter *adap);
 	void (*unprepare_recovery)(struct i2c_adapter *adap);
-- 
2.11.0

[PATCH 2/2] i2c: rcar: use the new get_bus_free callback

[Wolfram Sang]

To break out of recovery as early as possible, feed back the bus_free
logic state.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/i2c/busses/i2c-rcar.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index 5e310efd9446..76154747971e 100644
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -179,8 +179,6 @@ static void rcar_i2c_set_scl(struct i2c_adapter *adap, int val)
 	rcar_i2c_write(priv, ICMCR, priv->recovery_icmcr);
 };
 
-/* No get_sda, because the HW only reports its bus free logic, not SDA itself */
-
 static void rcar_i2c_set_sda(struct i2c_adapter *adap, int val)
 {
 	struct rcar_i2c_priv *priv = i2c_get_adapdata(adap);
@@ -193,10 +191,19 @@ static void rcar_i2c_set_sda(struct i2c_adapter *adap, int val)
 	rcar_i2c_write(priv, ICMCR, priv->recovery_icmcr);
 };
 
+static int rcar_i2c_get_bus_free(struct i2c_adapter *adap)
+{
+	struct rcar_i2c_priv *priv = i2c_get_adapdata(adap);
+
+	return !(rcar_i2c_read(priv, ICMCR) & FSDA);
+
+};
+
 static struct i2c_bus_recovery_info rcar_i2c_bri = {
 	.get_scl = rcar_i2c_get_scl,
 	.set_scl = rcar_i2c_set_scl,
 	.set_sda = rcar_i2c_set_sda,
+	.get_bus_free = rcar_i2c_get_bus_free,
 	.recover_bus = i2c_generic_scl_recovery,
 };
 static void rcar_i2c_init(struct rcar_i2c_priv *priv)
@@ -211,7 +218,7 @@ static void rcar_i2c_init(struct rcar_i2c_priv *priv)
 
 static int rcar_i2c_bus_barrier(struct rcar_i2c_priv *priv)
 {
-	int i, ret;
+	int i;
 
 	for (i = 0; i < LOOP_TIMEOUT; i++) {
 		/* make sure that bus is not busy */
@@ -222,13 +229,7 @@ static int rcar_i2c_bus_barrier(struct rcar_i2c_priv *priv)
 
 	/* Waiting did not help, try to recover */
 	priv->recovery_icmcr = MDBS | OBPC | FSDA | FSCL;
-	ret = i2c_recover_bus(&priv->adap);
-
-	/* No failure when recovering, so check bus busy bit again */
-	if (ret == 0)
-		ret = (rcar_i2c_read(priv, ICMCR) & FSDA) ? -EBUSY : 0;
-
-	return ret;
+	return i2c_recover_bus(&priv->adap);
 }
 
 static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv, struct i2c_timings *t)
-- 
2.11.0

Re: [PATCH 1/2] i2c: recovery: add get_bus_free callback

[Peter Rosin]

On 2018-07-11 00:24, Wolfram Sang wrote:
> Some IP cores have an internal 'bus free' logic which may be more
> advanced than just checking if SDA is high. Add a separate callback to
> get this status. Filling it is optional.
> 
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
>  drivers/i2c/i2c-core-base.c | 27 +++++++++++++++++++++++----
>  include/linux/i2c.h         |  3 +++
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index c7995efd58ea..59f8dfc5be36 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -158,6 +158,22 @@ static void set_sda_gpio_value(struct i2c_adapter *adap, int val)
>  	gpiod_set_value_cansleep(adap->bus_recovery_info->sda_gpiod, val);
>  }
>  
> +static int i2c_generic_bus_free(struct i2c_adapter *adap)
> +{
> +	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
> +	int ret = -EOPNOTSUPP;
> +
> +	if (bri->get_bus_free)
> +		ret = bri->get_bus_free(adap);
> +	else if (bri->get_sda)
> +		ret = bri->get_sda(adap);
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	return ret ? 0 : -EBUSY;
> +}

Hmmm, the name i2c_generic_bus_free suggests that scl should also be checked,
because the *bus* isn't really free unless both lines are high? No? Or, maybe
just rename to i2c_generic_sda_free (or something)?

But that's of course just a nit...

More importantly, isn't a ->get_bus_free implementation a sufficient requirement
for recovery? I.e. even if both ->get_sda and ->set_sda are missing?

Cheers,
Peter

> +
>  /*
>   * We are generating clock pulses. ndelay() determines durating of clk pulses.
>   * We will generate clock with rate 100 KHz and so duration of both clock levels
> @@ -169,7 +185,7 @@ static void set_sda_gpio_value(struct i2c_adapter *adap, int val)
>  int i2c_generic_scl_recovery(struct i2c_adapter *adap)
>  {
>  	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
> -	int i = 0, val = 1, ret = 0;
> +	int i = 0, val = 1, ret;
>  
>  	if (bri->prepare_recovery)
>  		bri->prepare_recovery(adap);
> @@ -207,14 +223,17 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
>  			bri->set_sda(adap, val);
>  		ndelay(RECOVERY_NDELAY / 2);
>  
> -		/* Break if SDA is high */
> -		if (val && bri->get_sda) {
> -			ret = bri->get_sda(adap) ? 0 : -EBUSY;
> +		if (val) {
> +			ret = i2c_generic_bus_free(adap);
>  			if (ret == 0)
>  				break;
>  		}
>  	}
>  
> +	/* If we can't check bus status, assume recovery worked */
> +	if (ret == -EOPNOTSUPP)
> +		ret = 0;
> +
>  	if (bri->unprepare_recovery)
>  		bri->unprepare_recovery(adap);
>  
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 9d1818c56775..60e224428a85 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -587,6 +587,8 @@ struct i2c_timings {
>   * @set_sda: This sets/clears the SDA line. This or get_sda() is mandatory for
>   *	generic SCL recovery. Populated internally, if sda_gpio is a valid GPIO,
>   *	for generic GPIO recovery.
> + * @get_bus_free: Returns the bus free state as seen from the IP core in case it
> + *	has a more complex internal logic than just reading SDA. Optional.
>   * @prepare_recovery: This will be called before starting recovery. Platform may
>   *	configure padmux here for SDA/SCL line or something else they want.
>   * @unprepare_recovery: This will be called after completing recovery. Platform
> @@ -601,6 +603,7 @@ struct i2c_bus_recovery_info {
>  	void (*set_scl)(struct i2c_adapter *adap, int val);
>  	int (*get_sda)(struct i2c_adapter *adap);
>  	void (*set_sda)(struct i2c_adapter *adap, int val);
> +	int (*get_bus_free)(struct i2c_adapter *adap);
>  
>  	void (*prepare_recovery)(struct i2c_adapter *adap);
>  	void (*unprepare_recovery)(struct i2c_adapter *adap);
> 

Re: [PATCH 1/2] i2c: recovery: add get_bus_free callback

[Wolfram Sang]

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> Hmmm, the name i2c_generic_bus_free suggests that scl should also be checked,
> because the *bus* isn't really free unless both lines are high? No? Or, maybe
> just rename to i2c_generic_sda_free (or something)?

Well, technically, bus recovery is just for resurrecting a stuck low
SDA. So, I'd think checking if SDA went high again should do it.

However, there is HW (at least Renesas R-Car) which cannot read SDA
directly. It will just return the result of its internal 'bus_free'
logic. Whatever that is. I think it wants to see a STOP but that may be
only part of it.

I wanted to have an option to make use of such a feature if we can't
read SDA. It is better than nothing. But since it doesn't reflect the
state of SDA directly, I decided for another callback.

> More importantly, isn't a ->get_bus_free implementation a sufficient requirement
> for recovery? I.e. even if both ->get_sda and ->set_sda are missing?

In my case, it isn't. It needs set_sda (== STOP) to achieve a useful
result. Hmm, I think this needs better documentation...


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Re: [PATCH 1/2] i2c: recovery: add get_bus_free callback

[Wolfram Sang]

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> > More importantly, isn't a ->get_bus_free implementation a sufficient requirement
> > for recovery? I.e. even if both ->get_sda and ->set_sda are missing?
> 
> In my case, it isn't. It needs set_sda (== STOP) to achieve a useful
> result. Hmm, I think this needs better documentation...

On a second thought, it may be possible to simply merge get_sda and
get_bus_free in the future. For now, I'd like to keep them seperate
until we have implemented bus recovery for some more hardware.


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Re: [PATCH 1/2] i2c: recovery: add get_bus_free callback

[Wolfram Sang]

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On Wed, Jul 11, 2018 at 12:24:22AM +0200, Wolfram Sang wrote:
> Some IP cores have an internal 'bus free' logic which may be more
> advanced than just checking if SDA is high. Add a separate callback to
> get this status. Filling it is optional.
> 
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Applied to for-next, thanks!


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Re: [PATCH 2/2] i2c: rcar: use the new get_bus_free callback

[Wolfram Sang]

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On Wed, Jul 11, 2018 at 12:24:23AM +0200, Wolfram Sang wrote:
> To break out of recovery as early as possible, feed back the bus_free
> logic state.
> 
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Applied to for-next, thanks!


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