linux-kernel - Re: [PATCH 03/10] mfd / platform: cros_ec: Miscellaneous character device to talk with the EC

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Date:   Tue, 4 Jun 2019 20:59:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Guenter Roeck <groeck@...gle.com>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Lee Jones <lee.jones@...aro.org>, kernel@...labora.com,
        Dmitry Torokhov <dtor@...omium.org>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-doc@...r.kernel.org, Enno Luebbers <enno.luebbers@...el.com>,
        Guido Kiener <guido@...ner-muenchen.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kishon Vijay Abraham I <kishon@...com>,
        Jonathan Corbet <corbet@....net>, Wu Hao <hao.wu@...el.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Jilayne Lovejoy <opensource@...ayne.com>
Subject: Re: [PATCH 03/10] mfd / platform: cros_ec: Miscellaneous character
 device to talk with the EC

On Tue, Jun 04, 2019 at 11:39:21AM -0700, Guenter Roeck wrote:
> On Tue, Jun 4, 2019 at 11:35 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Tue, Jun 04, 2019 at 01:58:38PM -0300, Ezequiel Garcia wrote:
> > > Hey Greg,
> > >
> > > > > + dev_info(&pdev->dev, "Created misc device /dev/%s\n",
> > > > > +          data->misc.name);
> > > >
> > > > No need to be noisy, if all goes well, your code should be quiet.
> > > >
> > >
> > > I sometimes wonder about this being noise or not, so I will slightly
> > > hijack this thread for this discussion.
> > >
> > > >From a kernel developer point-of-view, or even from a platform
> > > developer or user with a debugging hat point-of-view, having
> > > a "device created" or "device registered" message is often very useful.
> >
> > For you, yes.  For someone with 30000 devices attached to their system,
> > it is not, and causes booting to take longer than it should be.
> >
> > > In fact, I wish people would do this more often, so I don't have to
> > > deal with dynamic debug, or hack my way:
> > >
> > > diff --git a/drivers/media/i2c/ov5647.c b/drivers/media/i2c/ov5647.c
> > > index 4589631798c9..473549b26bb2 100644
> > > --- a/drivers/media/i2c/ov5647.c
> > > +++ b/drivers/media/i2c/ov5647.c
> > > @@ -603,7 +603,7 @@ static int ov5647_probe(struct i2c_client *client,
> > >         if (ret < 0)
> > >                 goto error;
> > >
> > > -       dev_dbg(dev, "OmniVision OV5647 camera driver probed\n");
> > > +       dev_info(dev, "OmniVision OV5647 camera driver probed\n");
> > >         return 0;
> > >  error:
> > >         media_entity_cleanup(&sd->entity);
> > >
> > > In some subsystems, it's even a behavior I'm more or less relying on:
> > >
> > > $ git grep v4l2_info.*registered drivers/media/ | wc -l
> > > 26
> > >
> > > And on the downsides, I can't find much. It's just one little line,
> > > that is not even noticed unless you have logging turned on.
> >
> > Its better to be quiet, which is why the "default driver registration"
> > macros do not have any printk messages in them.  When converting drivers
> > over to it, we made the boot process much more sane, don't try to go and
> > add messages for no good reason back in please.
> >
> > dynamic debugging can be enabled on a module and line-by-line basis,
> > even from the boot command line.  So if you need debugging, you can
> > always ask someone to just reboot or unload/load the module and get the
> > message that way.
> >
> 
> Can we by any chance make this an official policy ? I am kind of tired
> having to argue about this over and over again.

Sure, but how does anyone make any "official policy" in the kernel?  :)

I could just go through and delete all "look ma, a new driver/device!"
messages, but that might be annoying...

thanks,

greg k-h