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

From: Johan Hovold <johan@kernel.org>
To: Lee Jones <lee.jones@linaro.org>
Cc: balbi@kernel.org, david.brown@linaro.org,
	gregkh@linuxfoundation.org, linus.walleij@linaro.org,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	wsa+renesas@sang-engineering.com, alokc@codeaurora.org,
	kramasub@codeaurora.org, linux-i2c@vger.kernel.org,
	linux-gpio@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	andy.gross@linaro.org, jlhugo@gmail.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/8] i2c: i2c-qcom-geni: Signify successful driver probe
Date: Wed, 5 Jun 2019 09:56:56 +0200	[thread overview]
Message-ID: <20190605075656.GC29637@localhost> (raw)
In-Reply-To: <20190605071625.GK4797@dell>

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@linaro.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

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