[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Russell King]

smbus functions return -ve on error, 0 on success.  However,
__i2c_transfer() have a different return signature - -ve on error, or
number of buffers transferred (which may be zero or greater.)

The upshot of this is that the sense of the test is reversed when using
the mux on a bus supporting the master_xfer method: we cache the value
and never retry if we fail to transfer any buffers, but if we succeed,
we clear the cached value.

Fix this.

Fixes: 463e8f845cbf ("i2c: mux: pca954x: retry updating the mux selection on failure")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 drivers/i2c/muxes/i2c-mux-pca954x.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..b6d62ecbd5b6 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -179,7 +179,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret >= 0 ? regval : 0;
 	}
 
 	return ret;
-- 
2.7.4

[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Russell King]

smbus functions return -ve on error, 0 on success.  However,
__i2c_transfer() have a different return signature - -ve on error, or
number of buffers transferred (which may be zero or greater.)

The upshot of this is that the sense of the test is reversed when using
the mux on a bus supporting the master_xfer method: we cache the value
and never retry if we fail to transfer any buffers, but if we succeed,
we clear the cached value.

Fix this.

Fixes: 463e8f845cbf ("i2c: mux: pca954x: retry updating the mux selection on failure")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 drivers/i2c/muxes/i2c-mux-pca954x.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..b6d62ecbd5b6 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -179,7 +179,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret >= 0 ? regval : 0;
 	}
 
 	return ret;
-- 
2.7.4

Re: [PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Peter Rosin]

On 2016-12-16 21:06, Russell King wrote:
> smbus functions return -ve on error, 0 on success.  However,
> __i2c_transfer() have a different return signature - -ve on error, or
> number of buffers transferred (which may be zero or greater.)
> 
> The upshot of this is that the sense of the test is reversed when using
> the mux on a bus supporting the master_xfer method: we cache the value
> and never retry if we fail to transfer any buffers, but if we succeed,
> we clear the cached value.

Ouch! Thanks for catching this.

> Fix this.

But lets fix the corner case of __i2c_transfer returning 0 instead of
the expected 1 as well (not sure if that's even possible, but lets close
the possibility just in case), so I'd prefer if you could fix
pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
instead, and -EREMOTEIO on other non-negative return values. Thanks!

Cheers,
peda

> Fixes: 463e8f845cbf ("i2c: mux: pca954x: retry updating the mux selection on failure")
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> ---
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 8bc3d36d2837..b6d62ecbd5b6 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -179,7 +179,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
>  	/* Only select the channel if its different from the last channel */
>  	if (data->last_chan != regval) {
>  		ret = pca954x_reg_write(muxc->parent, client, regval);
> -		data->last_chan = ret ? 0 : regval;
> +		data->last_chan = ret >= 0 ? regval : 0;
>  	}
>  
>  	return ret;
> 

[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Peter Rosin]

On 2016-12-16 21:06, Russell King wrote:
> smbus functions return -ve on error, 0 on success.  However,
> __i2c_transfer() have a different return signature - -ve on error, or
> number of buffers transferred (which may be zero or greater.)
> 
> The upshot of this is that the sense of the test is reversed when using
> the mux on a bus supporting the master_xfer method: we cache the value
> and never retry if we fail to transfer any buffers, but if we succeed,
> we clear the cached value.

Ouch! Thanks for catching this.

> Fix this.

But lets fix the corner case of __i2c_transfer returning 0 instead of
the expected 1 as well (not sure if that's even possible, but lets close
the possibility just in case), so I'd prefer if you could fix
pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
instead, and -EREMOTEIO on other non-negative return values. Thanks!

Cheers,
peda

> Fixes: 463e8f845cbf ("i2c: mux: pca954x: retry updating the mux selection on failure")
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> ---
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 8bc3d36d2837..b6d62ecbd5b6 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -179,7 +179,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
>  	/* Only select the channel if its different from the last channel */
>  	if (data->last_chan != regval) {
>  		ret = pca954x_reg_write(muxc->parent, client, regval);
> -		data->last_chan = ret ? 0 : regval;
> +		data->last_chan = ret >= 0 ? regval : 0;
>  	}
>  
>  	return ret;
> 

Re: [PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Russell King - ARM Linux]

On Fri, Dec 16, 2016 at 10:20:35PM +0100, Peter Rosin wrote:
> On 2016-12-16 21:06, Russell King wrote:
> > smbus functions return -ve on error, 0 on success.  However,
> > __i2c_transfer() have a different return signature - -ve on error, or
> > number of buffers transferred (which may be zero or greater.)
> > 
> > The upshot of this is that the sense of the test is reversed when using
> > the mux on a bus supporting the master_xfer method: we cache the value
> > and never retry if we fail to transfer any buffers, but if we succeed,
> > we clear the cached value.
> 
> Ouch! Thanks for catching this.
> 
> > Fix this.
> 
> But lets fix the corner case of __i2c_transfer returning 0 instead of
> the expected 1 as well (not sure if that's even possible, but lets close
> the possibility just in case), so I'd prefer if you could fix
> pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
> instead, and -EREMOTEIO on other non-negative return values. Thanks!

So you want something like this instead?

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..9c4ac26c014e 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
 		buf[0] = val;
 		msg.buf = buf;
 		ret = __i2c_transfer(adap, &msg, 1);
+
+		if (ret >= 0 && ret != 1)
+			ret = -EREMOTEIO;
 	} else {
 		union i2c_smbus_data data;
 		ret = adap->algo->smbus_xfer(adap, client->addr,
@@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret < 0 ? 0 : regval;
 	}
 
 	return ret;


-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
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[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Russell King - ARM Linux]

On Fri, Dec 16, 2016 at 10:20:35PM +0100, Peter Rosin wrote:
> On 2016-12-16 21:06, Russell King wrote:
> > smbus functions return -ve on error, 0 on success.  However,
> > __i2c_transfer() have a different return signature - -ve on error, or
> > number of buffers transferred (which may be zero or greater.)
> > 
> > The upshot of this is that the sense of the test is reversed when using
> > the mux on a bus supporting the master_xfer method: we cache the value
> > and never retry if we fail to transfer any buffers, but if we succeed,
> > we clear the cached value.
> 
> Ouch! Thanks for catching this.
> 
> > Fix this.
> 
> But lets fix the corner case of __i2c_transfer returning 0 instead of
> the expected 1 as well (not sure if that's even possible, but lets close
> the possibility just in case), so I'd prefer if you could fix
> pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
> instead, and -EREMOTEIO on other non-negative return values. Thanks!

So you want something like this instead?

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..9c4ac26c014e 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
 		buf[0] = val;
 		msg.buf = buf;
 		ret = __i2c_transfer(adap, &msg, 1);
+
+		if (ret >= 0 && ret != 1)
+			ret = -EREMOTEIO;
 	} else {
 		union i2c_smbus_data data;
 		ret = adap->algo->smbus_xfer(adap, client->addr,
@@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret < 0 ? 0 : regval;
 	}
 
 	return ret;


-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently@9.6Mbps down 400kbps up
according to speedtest.net.

Re: [PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Peter Rosin]

On 2016-12-17 00:23, Russell King - ARM Linux wrote:
> On Fri, Dec 16, 2016 at 10:20:35PM +0100, Peter Rosin wrote:
>> On 2016-12-16 21:06, Russell King wrote:
>>> smbus functions return -ve on error, 0 on success.  However,
>>> __i2c_transfer() have a different return signature - -ve on error, or
>>> number of buffers transferred (which may be zero or greater.)
>>>
>>> The upshot of this is that the sense of the test is reversed when using
>>> the mux on a bus supporting the master_xfer method: we cache the value
>>> and never retry if we fail to transfer any buffers, but if we succeed,
>>> we clear the cached value.
>>
>> Ouch! Thanks for catching this.
>>
>>> Fix this.
>>
>> But lets fix the corner case of __i2c_transfer returning 0 instead of
>> the expected 1 as well (not sure if that's even possible, but lets close
>> the possibility just in case), so I'd prefer if you could fix
>> pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
>> instead, and -EREMOTEIO on other non-negative return values. Thanks!
> 
> So you want something like this instead?

Yes, but I was originally thinking that the second hunk was no
longer needed...

Either way,
Acked-by: Peter Rosin <peda@axentia.se>

Cheers,
peda


> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 8bc3d36d2837..9c4ac26c014e 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
>  		buf[0] = val;
>  		msg.buf = buf;
>  		ret = __i2c_transfer(adap, &msg, 1);
> +
> +		if (ret >= 0 && ret != 1)
> +			ret = -EREMOTEIO;
>  	} else {
>  		union i2c_smbus_data data;
>  		ret = adap->algo->smbus_xfer(adap, client->addr,
> @@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
>  	/* Only select the channel if its different from the last channel */
>  	if (data->last_chan != regval) {
>  		ret = pca954x_reg_write(muxc->parent, client, regval);
> -		data->last_chan = ret ? 0 : regval;
> +		data->last_chan = ret < 0 ? 0 : regval;
>  	}
>  
>  	return ret;
> 
> 

[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Peter Rosin]

On 2016-12-17 00:23, Russell King - ARM Linux wrote:
> On Fri, Dec 16, 2016 at 10:20:35PM +0100, Peter Rosin wrote:
>> On 2016-12-16 21:06, Russell King wrote:
>>> smbus functions return -ve on error, 0 on success.  However,
>>> __i2c_transfer() have a different return signature - -ve on error, or
>>> number of buffers transferred (which may be zero or greater.)
>>>
>>> The upshot of this is that the sense of the test is reversed when using
>>> the mux on a bus supporting the master_xfer method: we cache the value
>>> and never retry if we fail to transfer any buffers, but if we succeed,
>>> we clear the cached value.
>>
>> Ouch! Thanks for catching this.
>>
>>> Fix this.
>>
>> But lets fix the corner case of __i2c_transfer returning 0 instead of
>> the expected 1 as well (not sure if that's even possible, but lets close
>> the possibility just in case), so I'd prefer if you could fix
>> pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
>> instead, and -EREMOTEIO on other non-negative return values. Thanks!
> 
> So you want something like this instead?

Yes, but I was originally thinking that the second hunk was no
longer needed...

Either way,
Acked-by: Peter Rosin <peda@axentia.se>

Cheers,
peda


> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 8bc3d36d2837..9c4ac26c014e 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
>  		buf[0] = val;
>  		msg.buf = buf;
>  		ret = __i2c_transfer(adap, &msg, 1);
> +
> +		if (ret >= 0 && ret != 1)
> +			ret = -EREMOTEIO;
>  	} else {
>  		union i2c_smbus_data data;
>  		ret = adap->algo->smbus_xfer(adap, client->addr,
> @@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
>  	/* Only select the channel if its different from the last channel */
>  	if (data->last_chan != regval) {
>  		ret = pca954x_reg_write(muxc->parent, client, regval);
> -		data->last_chan = ret ? 0 : regval;
> +		data->last_chan = ret < 0 ? 0 : regval;
>  	}
>  
>  	return ret;
> 
> 

[PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Russell King]

smbus functions return -ve on error, 0 on success.  However,
__i2c_transfer() have a different return signature - -ve on error, or
number of buffers transferred (which may be zero or greater.)

The upshot of this is that the sense of the test is reversed when using
the mux on a bus supporting the master_xfer method: we cache the value
and never retry if we fail to transfer any buffers, but if we succeed,
we clear the cached value.

Fix this by making pca954x_reg_write() return a negative error code for
all failure cases.

Fixes: 463e8f845cbf ("i2c: mux: pca954x: retry updating the mux selection on failure")
Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 drivers/i2c/muxes/i2c-mux-pca954x.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..9c4ac26c014e 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
 		buf[0] = val;
 		msg.buf = buf;
 		ret = __i2c_transfer(adap, &msg, 1);
+
+		if (ret >= 0 && ret != 1)
+			ret = -EREMOTEIO;
 	} else {
 		union i2c_smbus_data data;
 		ret = adap->algo->smbus_xfer(adap, client->addr,
@@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret < 0 ? 0 : regval;
 	}
 
 	return ret;
-- 
2.7.4

Re: [PATCH] i2c: mux: pca954x: fix i2c mux selection caching

[Wolfram Sang]

[-- Attachment #1: Type: text/plain, Size: 857 bytes --]

On Sat, Dec 17, 2016 at 12:10:56PM +0000, Russell King wrote:
> smbus functions return -ve on error, 0 on success.  However,
> __i2c_transfer() have a different return signature - -ve on error, or
> number of buffers transferred (which may be zero or greater.)
> 
> The upshot of this is that the sense of the test is reversed when using
> the mux on a bus supporting the master_xfer method: we cache the value
> and never retry if we fail to transfer any buffers, but if we succeed,
> we clear the cached value.
> 
> Fix this by making pca954x_reg_write() return a negative error code for
> all failure cases.
> 
> Fixes: 463e8f845cbf ("i2c: mux: pca954x: retry updating the mux selection on failure")
> Acked-by: Peter Rosin <peda@axentia.se>
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

Applied to for-current, thanks!


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