linux-kernel - Re: [PATCH v7 08/34] i2c: tegra: Remove error message used for devm_request

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Date:   Mon, 21 Sep 2020 12:57:27 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 08/34] i2c: tegra: Remove error message used for
 devm_request_irq() failure

On Thu, Sep 17, 2020 at 05:59:28PM +0300, Dmitry Osipenko wrote:
> 17.09.2020 14:28, Thierry Reding пишет:
> > On Wed, Sep 09, 2020 at 01:39:40AM +0300, Dmitry Osipenko wrote:
> >> The error message prints number of vIRQ, which isn't a useful information.
> >> In practice devm_request_irq() never fails, hence let's remove the bogus
> >> message in order to make code cleaner.
> >>
> >> Reviewed-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> >> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> >> ---
> >>  drivers/i2c/busses/i2c-tegra.c | 4 +---
> >>  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > I think I have seen this fail occasionally when something's wrong in the
> > IRQ code, or when we are not properly configuring the IRQ in device tree
> > for example.
> > 
> > So I'd prefer if this error message stayed here. I agree that it's not a
> > terribly useful error message, so perhaps adding the error code to it
> > would make it more helpful?
> 
> We have dtbs_check nowadays and I assume you only saw a such problem
> during of hardware bring-up, correct?

dtbs_check is far from perfect, especially since only a handful of
bindings have been converted for Tegra. It's also not going to catch any
functional issues. You could still have a valid combination of flags
passed via DTB and still the interrupt allocation could fail because it
just so happens that the particular combination wasn't valid in that
particular setup.

> Realistically, this error should never happen "randomly" and even if it
> will happen, then you will still know that I2C driver failed because
> driver-core will tell you about that.

And yes, this is the type of error that you typically get during
bring-up and it does obviously go away once you've fixed it and then
tends not to come back. But that's exactly what happens with most errors
and having error messages helps in finding what went wrong.

If we drop the error message, then I may notice that the I2C driver
didn't probe correctly. But in order to find out why it didn't, I have
to go and add error messages to narrow down where I need to look. The
whole point of having error messages in the code is to avoid having to
go in and modify the code in order to troubleshoot.

In the interest of moving this along I'm fine with this for now. But I
suspect that we'll run into an issue with this eventually and that we'll
have to add an error message here again. If that happens we can always
reintroduce one, and perhaps at that time do a better job of making it
actually useful.

Reviewed-by: Thierry Reding <treding@...dia.com>

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