linux-kernel - Re: [PATCH] Revert "usb: gadget: Quieten gadget config message"

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Date:   Fri, 8 Jan 2021 10:16:42 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Albert Wang <albertccwang@...gle.com>, balbi@...nel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "usb: gadget: Quieten gadget config message"

On 21-01-07 10:50:38, Greg KH wrote:
> On Thu, Jan 07, 2021 at 09:06:04AM +0000, Albert Wang wrote:
> > This reverts commit 1cbfb8c4f62d667f6b8b3948949737edb92992cc.
> > 
> > The log of USB enumeration result is a useful log and only occupies
> > one line especially when USB3 enumeration failed and then downgrade
> > to USB2.
> > 
> > Signed-off-by: Albert Wang <albertccwang@...gle.com>
> > ---
> >  drivers/usb/gadget/composite.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> > index c6d455f2bb92..5b0d6103a63d 100644
> > --- a/drivers/usb/gadget/composite.c
> > +++ b/drivers/usb/gadget/composite.c
> > @@ -840,9 +840,9 @@ static int set_config(struct usb_composite_dev *cdev,
> >  		result = 0;
> >  	}
> >  
> > -	DBG(cdev, "%s config #%d: %s\n",
> > -	    usb_speed_string(gadget->speed),
> > -	    number, c ? c->label : "unconfigured");
> > +	INFO(cdev, "%s config #%d: %s\n",
> > +	     usb_speed_string(gadget->speed),
> > +	     number, c ? c->label : "unconfigured");
> 
> When everything is working properly, the kernel should be quiet.  If you
> have to see this message, you can turn it on at runtime, as Felipe
> pointed out, to enable it for your system.  But it's not a good default
> thing to have.

For most production kernel (or kernel ready for customers), it may not enable
CONFIG_DYNAMIC_DEBUG.

> 
> What do you need to see this message for?  What tool relies on it?  Who
> reads it?
> 

Usually, the developer him(her)self wants to read it to know if current
USB gadget enumerated and what speed is recognized, reading from the
console by eyes is the quickest way. Without this message, there is no
any messages when the USB gadget connects to host.

If enable debug message, there are too many messages, but I think most
developers may only need one information message to know if enumeration
is established correctly.

-- 

Thanks,
Peter Chen