linux-kernel - Re: [PATCH RFC 1/3] spmi: Linux driver framework for SPMI

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Message-ID: <20130816204055.GK4035@joshc.qualcomm.com>
Date:	Fri, 16 Aug 2013 15:40:55 -0500
From:	Josh Cartwright <joshc@...eaurora.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org,
	Sagar Dharia <sdharia@...eaurora.org>,
	Gilad Avidov <gavidov@...eaurora.org>,
	Michael Bohan <mbohan@...eaurora.org>
Subject: Re: [PATCH RFC 1/3] spmi: Linux driver framework for SPMI

On Fri, Aug 16, 2013 at 12:58:49PM -0700, Greg Kroah-Hartman wrote:
> On Fri, Aug 16, 2013 at 02:47:15PM -0500, Josh Cartwright wrote:
> > > > +#ifdef CONFIG_DEBUG_FS
> > > 
> > > Why?  If debugfs isn't enabled, the functions should just compile away
> > > with the debugfs_() calls, so no need to do this type of thing here,
> > > right?
> > 
> > Not sure I follow you, but it may be because this is a bit misleading.
> > 
> > Currently CONFIG_DEBUG_FS is being extended to also mean "do you want
> > the SPMI core to create device entries?".  It would probably make more
> > sense to have a CONFIG_SPMI_DEBUG option which is def_bool DEBUG_FS, as
> > other busses have.
> > 
> > The #ifdef here would then be #ifdef CONFIG_SPMI_DEBUG, as well as in
> > the Makefile:
> > 
> >   spmi-core-$(CONFIG_SPMI_DEBUG) += spmi-dbgfs.o
> 
> If debugfs is enabled why wouldn't you want debugfs entries for your
> devices?  Don't assume a user is going to be able to rebuild their
> kernel just for debugging stuff (hint, they usually aren't), so having
> these present, if they don't cause any performance issues, is usually
> best to always have around.

Okay, that makes sense.

So, backing up a step, you're original comment was regarding the
CONFIG_DEBUG_FS conditional in spmi-dbgfs.h:

On Fri, Aug 16, 2013 at 11:46:14AM -0700, Greg Kroah-Hartman wrote:
> > --- /dev/null
> > +++ b/drivers/spmi/spmi-dbgfs.h
> > @@ -0,0 +1,37 @@
> > +/* Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 and
> > + * only version 2 as published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +#ifndef _SPMI_DBGFS_H
> > +#define _SPMI_DBGFS_H
> > +
> > +#include <linux/spmi.h>
> > +#include <linux/debugfs.h>
> > +
> > +#ifdef CONFIG_DEBUG_FS
> 
> Why?  If debugfs isn't enabled, the functions should just compile away
> with the debugfs_() calls, so no need to do this type of thing here,
> right?

The reason why this is done is because the spmi debugfs support code is
is only built-in when CONFIG_DEBUG_FS is set.

Would you rather it always be built-in (well, whenever SPMI support is
included), and rely on the debugfs_* shims to handle the
!CONFIG_DEBUG_FS case?

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