linux-kernel - Re: [PATCH 2/8] i2c: i2c-qcom-geni: Signify successful driver probe

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Message-ID: <CAKv+Gu_YcdePUkkCGdP5DC9rxCUAshgOzU32pViAp2CbmAaJuw@mail.gmail.com>
Date:   Wed, 5 Jun 2019 09:22:59 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>, balbi@...nel.org,
        wsa+renesas@...g-engineering.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-usb <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Brown <david.brown@...aro.org>, alokc@...eaurora.org,
        kramasub@...eaurora.org, linux-i2c <linux-i2c@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Andy Gross <andy.gross@...aro.org>,
        Jeffrey Hugo <jlhugo@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/8] i2c: i2c-qcom-geni: Signify successful driver probe

On Wed, 5 Jun 2019 at 09:16, Lee Jones <lee.jones@...aro.org> wrote:
>
> On Tue, 04 Jun 2019, Bjorn Andersson wrote:
>
> > On Tue 04 Jun 03:44 PDT 2019, Lee Jones wrote:
> >
> > > The Qualcomm Geni I2C driver currently probes silently which can be
> > > confusing when debugging potential issues.  Add a low level (INFO)
> > > print when each I2C controller is successfully initially set-up.
> > >
> > > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > > ---
> > >  drivers/i2c/busses/i2c-qcom-geni.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> > > index 0fa93b448e8d..e27466d77767 100644
> > > --- a/drivers/i2c/busses/i2c-qcom-geni.c
> > > +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> > > @@ -598,6 +598,8 @@ static int geni_i2c_probe(struct platform_device *pdev)
> > >             return ret;
> > >     }
> > >
> > > +   dev_info(&pdev->dev, "Geni-I2C adaptor successfully added\n");
> > > +
> >
> > I would prefer that we do not add such prints, as it would be to accept
> > the downstream behaviour of spamming the log to the point where no one
> > will ever look through it.
>
> We should be able to find a middle ground.  Spamming the log with all
> sorts of device specific information/debug is obviously not
> constructive, but a single liner to advertise that an important
> device/controller has been successfully initialised is more helpful
> than it is hinderous.
>
> This print was added due to the silent initialisation costing me
> several hours of debugging ACPI device/driver code (albeit learning a
> lot about ACPI as I go) just to find out that it was already doing the
> right thing - just very quietly.
>

I agree.

There are numerous EHCI drivers IIRC which, if compiled in,
unconditionally print some blurb, whether you have the hardware or
not, which is pretty annoying.

In this case, however, having a single line per successfully probed
device (containing the dev_name and perhaps the MMIO base address or
some other identifying feature) is pretty useful, and shouldn't be
regarded as log spamming imo. dev_info() honours the 'quiet' kernel
command line parameter, and so you will only see the message if you
actually look at the log.