Subject: [PATCH 1/1] of: introduce helper to manage boolean

From: [email-masked] (Grant Likely)
Date: Fri, 09 Mar 2012 09:26:38 -0700

On Fri, 9 Mar 2012 11:04:35 +0100, Jean-Christophe PLAGNIOL-VILLARD <[email-masked]> wrote:
> On 18:44 Thu 08 Mar     , Grant Likely wrote:
> > On Tue,  7 Feb 2012 05:13:48 +0100, Jean-Christophe PLAGNIOL-VILLARD <[email-masked]> wrote:
> > > of_property_read_bool
> > > 
> > > Search for a property in a device node and read a 32-bit value from
> > > it. Returns 0 if <0> or if the property does not exist, 1 if <1> or none.
> > > 
> > > this will allow to disable a boolean
> > > 
> > > is-ok;          => true
> > > is-ok = <1>;    => true
> > > is-ok = <0>;    => false
> > > 
> > > Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <[email-masked]>
> > > Cc: devicetree-discuss at lists.ozlabs.org
> > > ---
> > > Hi,
> > > 
> > > 	if this is ok I'll rebase my mtd and i2c patch to use it
> > > 
> > > Best Regards,
> > > J.
> > >  drivers/of/base.c  |   30 ++++++++++++++++++++++++++++++
> > >  include/linux/of.h |    8 ++++++++
> > >  2 files changed, 38 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > > index 133908a..a0eaf08 100644
> > > --- a/drivers/of/base.c
> > > +++ b/drivers/of/base.c
> > > @@ -686,6 +686,36 @@ int of_property_read_u64(const struct device_node *np, const char *propname,
> > >  EXPORT_SYMBOL_GPL(of_property_read_u64);
> > >  
> > >  /**
> > > + * of_property_read_bool - Find and read a boolean from a property
> > > + * @np:		device node from which the property value is to be read.
> > > + * @propname:	name of the property to be searched.
> > > + *
> > > + * Search for a property in a device node and read a 32-bit value from
> > > + * it. Returns 0 if <0> or if the property does not exist, 1 if <1> or none.
> > > + *
> > > + * is-ok;	=> true
> > > + * is-ok = <1>;	=> true
> > > + * is-ok = <0>;	=> false
> > > + */
> > > +int of_property_read_bool(const struct device_node *np, const char *propname)
> > > +{
> > > +	u32 reg;
> > > +	int ret = of_property_read_u32(np, propname, &reg);
> > > +
> > > +	switch (ret) {
> > > +	case -EINVAL:
> > > +		return false;
> > > +	case -ENODATA:
> > > +		return true;
> > > +	case 0:
> > > +		return reg == 1;
> > 
> > Ugh.  so any value other than 1 returns false?  I think that will surprise
> > most people.
> > 
> > I don't like this api or binding.  If it is a bool property, then why isn't
> > simply testing for the property existance sufficient?
> no if you want to disable it
> 
> if a bool is define in the dtsi and want to disable it int the dts
> 
> if you we can do the the invert
> 
> if !0 => true
> 
> is-ok;			=> true
> is-ok = <val != 0>;	=> true
> is-ok = <0>;		=> false

This is a failure of the dtc tool, not the binding.  Accepting this binding
means we have to live with it for a very long time.  It needs to be fixed
in dtc instead so that properties can be deleted instead of only modified.

g.