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

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Date:   Wed, 5 Jun 2019 09:56:56 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>, balbi@...nel.org,
        wsa+renesas@...g-engineering.com, gregkh@...uxfoundation.org,
        linus.walleij@...aro.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, david.brown@...aro.org,
        alokc@...eaurora.org, kramasub@...eaurora.org,
        linux-i2c@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, andy.gross@...aro.org,
        jlhugo@...il.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/8] i2c: i2c-qcom-geni: Signify successful driver probe

On Wed, Jun 05, 2019 at 08:16:25AM +0100, Lee Jones 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.

No, we don't add noise like this to the logs just because it may be
useful while debugging. Even one-liners add up.

There are plenty of options for debugging already ranging from adding a
temporary dev_info() to the probe function in question to using dynamic
debugging to have driver core log every successful probe.

And in this case you say the driver was in fact already bound; that can
easily be verified through sysfs too in case things aren't behaving the
way you expect.

Johan