[PATCH 00/18] i2c: remove printout on handled timeouts

[PATCH 00/18] i2c: remove printout on handled timeouts

[Wolfram Sang]

While working on another cleanup series, I stumbled over the fact that
some drivers print an error on I2C or SMBus related timeouts. This is
wrong because it may be an expected state. The client driver on top
knows this, so let's keep error handling on this level and remove the
prinouts from controller drivers.

Looking forward to comments,

   Wolfram


Wolfram Sang (18):
  i2c: at91-master: remove printout on handled timeouts
  i2c: bcm-iproc: remove printout on handled timeouts
  i2c: bcm2835: remove printout on handled timeouts
  i2c: cadence: remove printout on handled timeouts
  i2c: davinci: remove printout on handled timeouts
  i2c: i801: remove printout on handled timeouts
  i2c: img-scb: remove printout on handled timeouts
  i2c: ismt: remove printout on handled timeouts
  i2c: nomadik: remove printout on handled timeouts
  i2c: omap: remove printout on handled timeouts
  i2c: qcom-geni: remove printout on handled timeouts
  i2c: qup: remove printout on handled timeouts
  i2c: rk3x: remove printout on handled timeouts
  i2c: sh_mobile: remove printout on handled timeouts
  i2c: st: remove printout on handled timeouts
  i2c: tegra: remove printout on handled timeouts
  i2c: uniphier-f: remove printout on handled timeouts
  i2c: uniphier: remove printout on handled timeouts

 drivers/i2c/busses/i2c-at91-master.c | 1 -
 drivers/i2c/busses/i2c-bcm-iproc.c   | 2 --
 drivers/i2c/busses/i2c-bcm2835.c     | 1 -
 drivers/i2c/busses/i2c-cadence.c     | 2 --
 drivers/i2c/busses/i2c-davinci.c     | 1 -
 drivers/i2c/busses/i2c-i801.c        | 4 ++--
 drivers/i2c/busses/i2c-img-scb.c     | 5 +----
 drivers/i2c/busses/i2c-ismt.c        | 1 -
 drivers/i2c/busses/i2c-nomadik.c     | 7 ++-----
 drivers/i2c/busses/i2c-omap.c        | 1 -
 drivers/i2c/busses/i2c-qcom-geni.c   | 5 +----
 drivers/i2c/busses/i2c-qup.c         | 4 +---
 drivers/i2c/busses/i2c-rk3x.c        | 3 ---
 drivers/i2c/busses/i2c-sh_mobile.c   | 1 -
 drivers/i2c/busses/i2c-st.c          | 5 +----
 drivers/i2c/busses/i2c-tegra.c       | 2 --
 drivers/i2c/busses/i2c-uniphier-f.c  | 1 -
 drivers/i2c/busses/i2c-uniphier.c    | 4 +---
 18 files changed, 9 insertions(+), 41 deletions(-)

-- 
2.43.0


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[PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Wolfram Sang]

I2C and SMBus timeouts are not something the user needs to be informed
about on controller level. The client driver may know if that really is
a problem and give more detailed information to the user. The controller
should just pass this information upwards. Remove the printout.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/i2c/busses/i2c-rk3x.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
index 086fdf262e7b..8c7367f289d3 100644
--- a/drivers/i2c/busses/i2c-rk3x.c
+++ b/drivers/i2c/busses/i2c-rk3x.c
@@ -1106,9 +1106,6 @@ static int rk3x_i2c_xfer_common(struct i2c_adapter *adap,
 		spin_lock_irqsave(&i2c->lock, flags);
 
 		if (timeout == 0) {
-			dev_err(i2c->dev, "timeout, ipd: 0x%02x, state: %d\n",
-				i2c_readl(i2c, REG_IPD), i2c->state);
-
 			/* Force a STOP condition without interrupt */
 			i2c_writel(i2c, 0, REG_IEN);
 			val = i2c_readl(i2c, REG_CON) & REG_CON_TUNING_MASK;
-- 
2.43.0


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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Heiko Stuebner]

Am Mittwoch, 10. April 2024, 13:24:27 CEST schrieb Wolfram Sang:
> I2C and SMBus timeouts are not something the user needs to be informed
> about on controller level. The client driver may know if that really is
> a problem and give more detailed information to the user. The controller
> should just pass this information upwards. Remove the printout.
> 
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Acked-by: Heiko Stuebner <heiko@sntech.de>


> ---
>  drivers/i2c/busses/i2c-rk3x.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
> index 086fdf262e7b..8c7367f289d3 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -1106,9 +1106,6 @@ static int rk3x_i2c_xfer_common(struct i2c_adapter *adap,
>  		spin_lock_irqsave(&i2c->lock, flags);
>  
>  		if (timeout == 0) {
> -			dev_err(i2c->dev, "timeout, ipd: 0x%02x, state: %d\n",
> -				i2c_readl(i2c, REG_IPD), i2c->state);
> -
>  			/* Force a STOP condition without interrupt */
>  			i2c_writel(i2c, 0, REG_IEN);
>  			val = i2c_readl(i2c, REG_CON) & REG_CON_TUNING_MASK;
> 





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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Dragan Simic]

Hello Wolfram,

On 2024-04-10 13:24, Wolfram Sang wrote:
> I2C and SMBus timeouts are not something the user needs to be informed
> about on controller level. The client driver may know if that really is
> a problem and give more detailed information to the user. The 
> controller
> should just pass this information upwards. Remove the printout.

Maybe it would be good to turn it into a debug message, instead of
simply removing it?  Maybe not all client drivers handle it correctly,
in which case having an easy way for debugging would be beneficial.

> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
>  drivers/i2c/busses/i2c-rk3x.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-rk3x.c 
> b/drivers/i2c/busses/i2c-rk3x.c
> index 086fdf262e7b..8c7367f289d3 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -1106,9 +1106,6 @@ static int rk3x_i2c_xfer_common(struct 
> i2c_adapter *adap,
>  		spin_lock_irqsave(&i2c->lock, flags);
> 
>  		if (timeout == 0) {
> -			dev_err(i2c->dev, "timeout, ipd: 0x%02x, state: %d\n",
> -				i2c_readl(i2c, REG_IPD), i2c->state);
> -
>  			/* Force a STOP condition without interrupt */
>  			i2c_writel(i2c, 0, REG_IEN);
>  			val = i2c_readl(i2c, REG_CON) & REG_CON_TUNING_MASK;

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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 274 bytes --]


> Maybe it would be good to turn it into a debug message, instead of
> simply removing it?  Maybe not all client drivers handle it correctly,
> in which case having an easy way for debugging would be beneficial.

Hmm, but it still returns -ETIMEDOUT to distinguish cases?


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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Dragan Simic]

On 2024-04-13 08:38, Wolfram Sang wrote:
>> Maybe it would be good to turn it into a debug message, instead of
>> simply removing it?  Maybe not all client drivers handle it correctly,
>> in which case having an easy way for debugging would be beneficial.
> 
> Hmm, but it still returns -ETIMEDOUT to distinguish cases?

Sure, but I think that having such an additional debug facility
can only help and save the people from adding temporary printk()s
while debugging.

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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 720 bytes --]

Hi Dragan,

> Sure, but I think that having such an additional debug facility
> can only help and save the people from adding temporary printk()s
> while debugging.

Mileages, I guess. I like temporary printouts for temporary debug
sessions. This way the upstream source code stays slim. In my experience
with I2C over the years, debugging happens with developers anyhow.
Logfiles from users which help developers create patches are very rare.
And those users are usually capable enough to add debug patches.
Given these experiences (which may be different in other subsystems), I
don't see why we should carry the bloat.

That said, I'll leave the final decision to the driver maintainers.

Happy hacking,

   Wolfram


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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Dragan Simic]

Hello Wolfram,

On 2024-04-13 09:10, Wolfram Sang wrote:
> Hi Dragan,
> 
>> Sure, but I think that having such an additional debug facility
>> can only help and save the people from adding temporary printk()s
>> while debugging.
> 
> Mileages, I guess. I like temporary printouts for temporary debug
> sessions. This way the upstream source code stays slim. In my 
> experience
> with I2C over the years, debugging happens with developers anyhow.
> Logfiles from users which help developers create patches are very rare.
> And those users are usually capable enough to add debug patches.
> Given these experiences (which may be different in other subsystems), I
> don't see why we should carry the bloat.

Yup, adding some printk()s while debugging is pretty much inevitable,
and having full debugging available would add a lot of code, regardless
of the subsystem.

> That said, I'll leave the final decision to the driver maintainers.

Agreed.

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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Heiko Stübner]

Am Samstag, 13. April 2024, 08:44:41 CEST schrieb Dragan Simic:
> On 2024-04-13 08:38, Wolfram Sang wrote:
> >> Maybe it would be good to turn it into a debug message, instead of
> >> simply removing it?  Maybe not all client drivers handle it correctly,
> >> in which case having an easy way for debugging would be beneficial.
> > 
> > Hmm, but it still returns -ETIMEDOUT to distinguish cases?
> 
> Sure, but I think that having such an additional debug facility
> can only help and save the people from adding temporary printk()s
> while debugging.

Also we're talking about two lines of code, I wouldn't call that bloat ;-)
I was thinking about dev_dbg vs. removal too, but hadn't a clear
favorite.

So essentially Dragan is tipping the scale and I guess dev_dbg might be
the nicer way to go.


Heiko



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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Dragan Simic]

Hello Heiko,

On 2024-04-13 09:58, Heiko Stübner wrote:
> Am Samstag, 13. April 2024, 08:44:41 CEST schrieb Dragan Simic:
>> On 2024-04-13 08:38, Wolfram Sang wrote:
>> >> Maybe it would be good to turn it into a debug message, instead of
>> >> simply removing it?  Maybe not all client drivers handle it correctly,
>> >> in which case having an easy way for debugging would be beneficial.
>> >
>> > Hmm, but it still returns -ETIMEDOUT to distinguish cases?
>> 
>> Sure, but I think that having such an additional debug facility
>> can only help and save the people from adding temporary printk()s
>> while debugging.
> 
> Also we're talking about two lines of code, I wouldn't call that bloat 
> ;-)
> I was thinking about dev_dbg vs. removal too, but hadn't a clear
> favorite.
> 
> So essentially Dragan is tipping the scale and I guess dev_dbg might be
> the nicer way to go.

Yes, the code for printing the message is already there and it's only
a couple of lines, so it might be a good idea to recycle it. :)

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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 568 bytes --]


> Also we're talking about two lines of code, I wouldn't call that bloat ;-)

With this patch, yes. But once you allow debug code, it is hard to draw
a line which debug is still okay and which is too fine-grained. And then
you end up with a lot. Over the years, I developed the tendency to try
to have less but meaningful error printouts. But I don't enforce it
strictly because it is too much bike-shedding discussion.

In case of this error printout here, it is just wrong. But, see, it also
came from this tendency I don't like to have printouts for every error.


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Re: [PATCH 13/18] i2c: rk3x: remove printout on handled timeouts

[Andi Shyti]

Hi,

On Sat, Apr 13, 2024 at 04:35:06PM +0200, Wolfram Sang wrote:
> > Also we're talking about two lines of code, I wouldn't call that bloat ;-)
> 
> With this patch, yes. But once you allow debug code, it is hard to draw
> a line which debug is still okay and which is too fine-grained. And then
> you end up with a lot. Over the years, I developed the tendency to try
> to have less but meaningful error printouts. But I don't enforce it
> strictly because it is too much bike-shedding discussion.
> 
> In case of this error printout here, it is just wrong. But, see, it also
> came from this tendency I don't like to have printouts for every error.

I agree with Wolfram here. Debug messages are OK if they are
providing real useful information to a final product.

Besides, as I explained earlier, the patter:

	dev_dbg("timed out")
	return -ETIMEDOUT;

(print a debug but return error) doesn't make much sense.

But, I this is all personal preference. So that I can also leave
it to the specific maintainer.

From my side all patches in this series are r-b'ed, except for
patch 6 where there are 3 dev_dbg in a row stating the same
thing.

Thanks Dragan and Heiko for your feedback.

Andi

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Re: [PATCH 00/18] i2c: remove printout on handled timeouts

[Andi Shyti]

Hi Wolfram,

On Wed, Apr 10, 2024 at 01:24:14PM +0200, Wolfram Sang wrote:
> While working on another cleanup series, I stumbled over the fact that
> some drivers print an error on I2C or SMBus related timeouts. This is
> wrong because it may be an expected state. The client driver on top
> knows this, so let's keep error handling on this level and remove the
> prinouts from controller drivers.
> 
> Looking forward to comments,
> 
>    Wolfram

Applyed everything but patch 6 in i2c/i2c-host on

git://git.kernel.org/pub/scm/linux/kernel/git/andi.shyti/linux.git

Thank you,
Andi

Patches applied
===============
[01/18] i2c: at91-master: remove printout on handled timeouts
        commit: 74cce8ed33aeac91f397d642901c94520e574f8b
[02/18] i2c: bcm-iproc: remove printout on handled timeouts
        commit: 9f98914320f3e332487042aa73bbbfacc1dc9896
[03/18] i2c: bcm2835: remove printout on handled timeouts
        commit: ab17612ffb60bf07e4268448e022576d42833bf7
[04/18] i2c: cadence: remove printout on handled timeouts
        commit: 7aaff22d3e939c5187512188d7e27eb5e93ae41e
[05/18] i2c: davinci: remove printout on handled timeouts
        commit: dc72daa5cdf1c6ffebaef0c6df1f4cdeb15cadd6
[07/18] i2c: img-scb: remove printout on handled timeouts
        commit: 3e720ba5e30d6dd1b22e0f8a23f1697d438092b8
[08/18] i2c: ismt: remove printout on handled timeouts
        commit: 800a297370161bda70a34cb00eb0fa2f0345b75f
[09/18] i2c: nomadik: remove printout on handled timeouts
        commit: 26fbd3025cbce49cb3dd71f3a10239f69546b3c2
[10/18] i2c: omap: remove printout on handled timeouts
        commit: d3f24197d8125b2bf75162ec5cc270fd68f894f4
[11/18] i2c: qcom-geni: remove printout on handled timeouts
        commit: 4677d9f5c98f1c2825de142de5df08621ea340b3
[12/18] i2c: qup: remove printout on handled timeouts
        commit: e28ec7512496848e8a340889c512a0167949dc8f
[13/18] i2c: rk3x: remove printout on handled timeouts
        commit: 1cf7a7b3c944f727f34453a132b8899685e32f81
[14/18] i2c: sh_mobile: remove printout on handled timeouts
        commit: 31fb960bf8a424c47a5bf4568685e058c9d6f24d
[15/18] i2c: st: remove printout on handled timeouts
        commit: bff862e67260f779b2188e4b39c1a9f9989532ee
[16/18] i2c: tegra: remove printout on handled timeouts
        commit: 5ea641d9ea5ee1b3536f8b75e658e3bf2c2a548e
[17/18] i2c: uniphier-f: remove printout on handled timeouts
        commit: c31bc8e162890cda38d045e73ff0004119ab28e7
[18/18] i2c: uniphier: remove printout on handled timeouts
        commit: 507a2da9539cdb839a1a2e57bfcca644bcfe0f03

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Re: [PATCH 00/18] i2c: remove printout on handled timeouts

[Andy Shevchenko]

Wed, Apr 10, 2024 at 01:24:14PM +0200, Wolfram Sang kirjoitti:
> While working on another cleanup series, I stumbled over the fact that
> some drivers print an error on I2C or SMBus related timeouts. This is
> wrong because it may be an expected state. The client driver on top
> knows this, so let's keep error handling on this level and remove the
> prinouts from controller drivers.
> 
> Looking forward to comments,

I do not see an equivalent change in I²C core.

IIRC in our case (DW or i801 or iSMT) we often have this message as the only
one that points to the issues (on non-debug level), it will be much harder to
debug for our customers with this going away.

-- 
With Best Regards,
Andy Shevchenko



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Re: [PATCH 00/18] i2c: remove printout on handled timeouts

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 1547 bytes --]

Hi Andy,

On Wed, Apr 24, 2024 at 03:08:14AM +0300, Andy Shevchenko wrote:
> Wed, Apr 10, 2024 at 01:24:14PM +0200, Wolfram Sang kirjoitti:
> > While working on another cleanup series, I stumbled over the fact that
> > some drivers print an error on I2C or SMBus related timeouts. This is
> > wrong because it may be an expected state. The client driver on top
> > knows this, so let's keep error handling on this level and remove the
> > prinouts from controller drivers.
> > 
> > Looking forward to comments,
> 
> I do not see an equivalent change in I²C core.

There shouldn't be. The core neither knows if it is okay or not. The
client driver knows.

> IIRC in our case (DW or i801 or iSMT) we often have this message as the only

Often? How often?

> one that points to the issues (on non-debug level), it will be much harder to
> debug for our customers with this going away.

The proper fix is to print the error in the client driver. Maybe this
needs a helper for client drivers which they can use like:

	i2c_report_error(client, retval, flags);

The other thing which is also more helpful IMO is that we have
trace_events for __i2c_transfer. There, you can see what was happening
on the bus before the timeout. It can easily be that, if device X
times out, it was because of the transfer before to device Y which locks
up the bus. A simple "Bus timed out" message will not help you a lot
there.

And, keep in mind the false positives I mentioned in the coverletter.

All the best,

   Wolfram


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Re: [PATCH 00/18] i2c: remove printout on handled timeouts

[Andy Shevchenko]

On Wed, Apr 24, 2024 at 12:00 PM Wolfram Sang
<wsa+renesas@sang-engineering.com> wrote:
> On Wed, Apr 24, 2024 at 03:08:14AM +0300, Andy Shevchenko wrote:
> > Wed, Apr 10, 2024 at 01:24:14PM +0200, Wolfram Sang kirjoitti:
> > > While working on another cleanup series, I stumbled over the fact that
> > > some drivers print an error on I2C or SMBus related timeouts. This is
> > > wrong because it may be an expected state. The client driver on top
> > > knows this, so let's keep error handling on this level and remove the
> > > prinouts from controller drivers.
> > >
> > > Looking forward to comments,
> >
> > I do not see an equivalent change in I²C core.
>
> There shouldn't be. The core neither knows if it is okay or not. The
> client driver knows.
>
> > IIRC in our case (DW or i801 or iSMT) we often have this message as the only
>
> Often? How often?

Once in a couple of months I assume. Last time it was a few weeks ago
that there was a report and they pointed to this very message which
was helpful.

> > one that points to the issues (on non-debug level), it will be much harder to
> > debug for our customers with this going away.
>
> The proper fix is to print the error in the client driver. Maybe this
> needs a helper for client drivers which they can use like:
>
>         i2c_report_error(client, retval, flags);
>
> The other thing which is also more helpful IMO is that we have
> trace_events for __i2c_transfer. There, you can see what was happening
> on the bus before the timeout. It can easily be that, if device X
> times out, it was because of the transfer before to device Y which locks
> up the bus. A simple "Bus timed out" message will not help you a lot
> there.

The trace events are good to have, not sure if production kernels have
them enabled, though.

> And, keep in mind the false positives I mentioned in the coverletter.


-- 
With Best Regards,
Andy Shevchenko

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Re: [PATCH 00/18] i2c: remove printout on handled timeouts

[Andy Shevchenko]

On Wed, Apr 24, 2024 at 3:41 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Wed, Apr 24, 2024 at 12:00 PM Wolfram Sang
> <wsa+renesas@sang-engineering.com> wrote:
> > On Wed, Apr 24, 2024 at 03:08:14AM +0300, Andy Shevchenko wrote:
> > > Wed, Apr 10, 2024 at 01:24:14PM +0200, Wolfram Sang kirjoitti:
> > > > While working on another cleanup series, I stumbled over the fact that
> > > > some drivers print an error on I2C or SMBus related timeouts. This is
> > > > wrong because it may be an expected state. The client driver on top
> > > > knows this, so let's keep error handling on this level and remove the
> > > > prinouts from controller drivers.
> > > >
> > > > Looking forward to comments,
> > >
> > > I do not see an equivalent change in I²C core.
> >
> > There shouldn't be. The core neither knows if it is okay or not. The
> > client driver knows.
> >
> > > IIRC in our case (DW or i801 or iSMT) we often have this message as the only
> >
> > Often? How often?
>
> Once in a couple of months I assume. Last time it was a few weeks ago
> that there was a report and they pointed to this very message which
> was helpful.
>
> > > one that points to the issues (on non-debug level), it will be much harder to
> > > debug for our customers with this going away.
> >
> > The proper fix is to print the error in the client driver. Maybe this
> > needs a helper for client drivers which they can use like:
> >
> >         i2c_report_error(client, retval, flags);
> >
> > The other thing which is also more helpful IMO is that we have
> > trace_events for __i2c_transfer. There, you can see what was happening
> > on the bus before the timeout. It can easily be that, if device X
> > times out, it was because of the transfer before to device Y which locks
> > up the bus. A simple "Bus timed out" message will not help you a lot
> > there.
>
> The trace events are good to have, not sure if production kernels have
> them enabled, though.

Ah, and to accent on the usefulness of the message that happens before
one thinks about enabling trace events. How usual is that we _expect_
something to fail? Deeper debugging usually happens after we have
noticed the issue. I'm not sure if there is an equivalent to signal
about a problem without expecting it to happen. Is that -ETIMEDOUT
being converted to some message somewhere?

> > And, keep in mind the false positives I mentioned in the coverletter.



-- 
With Best Regards,
Andy Shevchenko

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Re: [PATCH 00/18] i2c: remove printout on handled timeouts

[Wolfram Sang]

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> about a problem without expecting it to happen. Is that -ETIMEDOUT
> being converted to some message somewhere?

As said initially, the place for that is the client driver, I'd say.


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