| Message ID | 20240410112418.6400-20-wsa+renesas@sang-engineering.com |
|---|---|
| Headers | show |
| Series | i2c: remove printout on handled timeouts | expand |
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
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. :)
> 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.
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.
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.
> 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.