linux-kernel - Re: [PATCH] regmap: Add Kconfig option for debugfs register writes

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Message-ID: <20140617201347.GA32450@pengutronix.de>
Date:	Tue, 17 Jun 2014 22:13:47 +0200
From:	Markus Pargmann <mpa@...gutronix.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kernel@...gutronix.de,
	Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH] regmap: Add Kconfig option for debugfs register writes

Hi,

On Tue, Jun 17, 2014 at 12:56:54PM -0700, David Rientjes wrote:
> On Tue, 17 Jun 2014, Markus Pargmann wrote:
> 
> > To enable writing of registers through the regmap debugfs interface, it
> > was necessary to alter the regmap-debugfs.c source code. This is not
> > really practical.
> > 
> > As this is a powerful tool for debugging, this patch creates an expert
> > kconfig option for this function. This makes it easier to enable
> > register writing in the kernel.
> > 
> > This patch also fixes the file mode when the regmap debugfs write code is
> > compiled.
> > 
> 
> Forcing users to enable CONFIG_EXPERT for this doesn't seem appropriate, 
> it enables things by default and has really become a separate config of 
> its own.  You might want to consider removing this dependency unless you 
> have a strong reason for keeping it.

I only created the dependency on CONFIG_EXPERT to make it clear that
this option is only for people who know what they are doing. I can
remove that dependency if that is OK for everyone?

Thanks,

Markus

> 
> > Cc: Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>
> > Signed-off-by: Markus Pargmann <mpa@...gutronix.de>
> > ---
> >  drivers/base/regmap/Kconfig          | 14 ++++++++++++++
> >  drivers/base/regmap/regmap-debugfs.c | 16 ++++++++++------
> >  2 files changed, 24 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/base/regmap/Kconfig b/drivers/base/regmap/Kconfig
> > index 4251570610c9..ce86600dbe75 100644
> > --- a/drivers/base/regmap/Kconfig
> > +++ b/drivers/base/regmap/Kconfig
> > @@ -23,3 +23,17 @@ config REGMAP_MMIO
> >  
> >  config REGMAP_IRQ
> >  	bool
> > +
> > +config REGMAP_ALLOW_WRITE_DEBUGFS
> > +	default n
> > +	depends on DEBUG_FS
> > +	depends on EXPERT
> > +	depends on REGMAP
> > +	bool "Regmap, allow direct register writes through debugfs"
> > +	help
> > +	  This option enables regmap debugfs write support. If this is enabled,
> > +	  you can directly write registers using the registers file in the
> > +	  regmap debugfs.
> > +
> > +	  This is potentially dangerous. Do not enable this option unless you
> > +	  know what you are doing.
> > diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c
> > index 45d812c0ea77..12906f2bdf00 100644
> > --- a/drivers/base/regmap/regmap-debugfs.c
> > +++ b/drivers/base/regmap/regmap-debugfs.c
> > @@ -261,13 +261,10 @@ static ssize_t regmap_map_read_file(struct file *file, char __user *user_buf,
> >  				   count, ppos);
> >  }
> >  
> > -#undef REGMAP_ALLOW_WRITE_DEBUGFS
> > -#ifdef REGMAP_ALLOW_WRITE_DEBUGFS
> > +#if IS_ENABLED(CONFIG_REGMAP_ALLOW_WRITE_DEBUGFS)
> >  /*
> >   * This can be dangerous especially when we have clients such as
> > - * PMICs, therefore don't provide any real compile time configuration option
> > - * for this feature, people who want to use this will need to modify
> > - * the source code directly.
> > + * PMICs, therefore this function can only be selected in expert kconfig mode.
> >   */
> >  static ssize_t regmap_map_write_file(struct file *file,
> >  				     const char __user *user_buf,
> > @@ -512,7 +509,14 @@ void regmap_debugfs_init(struct regmap *map, const char *name)
> >  			    map, &regmap_reg_ranges_fops);
> >  
> >  	if (map->max_register || regmap_readable(map, 0)) {
> > -		debugfs_create_file("registers", 0400, map->debugfs,
> > +		unsigned int registers_mode;
> > +
> > +		if (IS_ENABLED(CONFIG_REGMAP_ALLOW_WRITE_DEBUGFS))
> > +			registers_mode = 0600;
> > +		else
> > +			registers_mode = 0400;
> > +
> > +		debugfs_create_file("registers", registers_mode, map->debugfs,
> >  				    map, &regmap_map_fops);
> >  		debugfs_create_file("access", 0400, map->debugfs,
> >  				    map, &regmap_access_fops);
> 

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