RE: [PATCH v3] mfd: syscon: Decouple syscon interface from platform devices

[Pankaj Dubey <pankaj.dubey@samsung.com>]

Hi,

On September 18, 2014 1:26, Dong Aisheng wrote
> On Thu, Sep 18, 2014 at 11:33:26AM +0530, Pankaj Dubey wrote:
> > Hi,
> >
> > Adding CC to Xiubo Li, Geert Uytterhoeven and Stephen Warren.
> >
> > On Thursday, September 18, 2014, Dong Aisheng wrote,
> > > On Wed, Sep 17, 2014 at 04:50:50PM +0530, Pankaj Dubey wrote:
> > > > Hi,
> > > >
> > > > On Wednesday, September 17, 2014, Dong Aisheng Wrote,
> > > > > >
> > > > > > +	regmap = regmap_init_mmio(NULL, base,
> > &syscon_regmap_config);
> > > > >
> > > > > Does a NULL device pointer work?
> > > >
> > > > Yes, it is safe, at least we are able to test on Exynos based SoC.
> > > > I have tested it with kgene/for-next kernel on Exynos3250.
> > > > Also it has been tested on Exynos5250 based Snow board with
> > > > 3.17-rc5 based kernel by Vivek Gautam.
> > > >
> > > > Patch V2 also has been tested by "Borris Brezillon" on AT91
platform.
> > > >
> > > >
> > >
> > > The kernel i tested was next-20140915 of linux-next.
> > >
> > > please see regmap_get_val_endian called in regmap_init function.
> > > static enum regmap_endian regmap_get_val_endian(struct device *dev,
> > >                                         const struct regmap_bus *bus,
> > >                                         const struct regmap_config
> > *config) {
> > >         struct device_node *np = dev->of_node;
> > >         enum regmap_endian endian;
> > > ...
> > > }
> > > It will crash at the first line of dev->of_node if dev is NULL.
> > >
> > > Can you check if you're using the same code as mine?
> >
> > No, it's not same.
> > My bad that I was not using linux-next for testing this patch.
> > We tested on kgene/for-next where these changes still have not come.
> > Just now I checked linux-next and found that it will crash at first
> > line of "regmap_get_val_endian" as there is no check for NULL on dev.
> >
> > I checked git history of regmap.c file and found recently this file
> > has been modified for adding DT endianness binding support. Following
> > are set of patches gone for this
> >
> > cf673fb regmap: Split regmap_get_endian() in two functions 5844a8b
> > regmap: Fix handling of volatile registers for format_write() chips
> > 45e1a27 regmap: of_regmap_get_endian() cleanup ba1b53f regmap: Fix DT
> > endianess parsing logic
> > d647c19 regmap: add DT endianness binding support.
> >
> > I think there should have been a check for NULL on "dev" in
> > "regmap_get_val_endian", so that if dev pointer exist then only it
> > makes sense to get endianness property from DT.
> >
> > I will suggest following fix in regmap.c for this. With following fix
> > I tested it and it works well on linux-next also. So if you can
> > confirm following fix is working for you then I can post this patch.
> >
> 
> I tested the patch work.

Thanks for testing. In that case I will post this change, as I feel this
should be
fixed irrespective of my syscon patch.

> But as Xiubo pointed in another mail, it may still cause other issues.
> Looking at regmap.c, there're still some other places using the device
pointer, e.g.
> dev_xxx debug information and some tracepoints also take device pointer as
> parameter(not sure if it will break if dev is NULL).
> Another thing is that if dev is NULL, we may not be able to use regmap
debugfs
> feature which seems also not as our expected.
> 

I would have preferred to check dev for NULL, as it's only at two places and
we could
still have debug prints for NULL dev, as normal pr_info instead of dev_info.

But Xiubo also pointed out that his patch [1] which updates syscon binding
information
will be useless if we pass NULL dev in regmap_init_mmio, which he posted
today,
and it requires dev pointer in "regmap_get_val_endian" function to read DT
property.

[1]: [PATCH] mfd: syscon: binding: Add syscon endianness support
      https://lkml.org/lkml/2014/9/18/67

So instead of adding dummy device or creating device structure, I would
prefer to get actual
device pointer corresponding to "np" passed in of_syscon_register function
as shown below:

----
static struct syscon *of_syscon_register(struct device_node *np)
 {
+	struct platform_device *pdev;
 	struct syscon *syscon;
 	struct regmap *regmap;
 	void __iomem *base;
@@ -142,7 +144,11 @@ static struct syscon *of_syscon_register(struct
device_node *np)
 	if (!base)
 		return ERR_PTR(-ENOMEM);
 
-	regmap = regmap_init_mmio(NULL, base, &syscon_regmap_config);
+	pdev = of_find_device_by_node(np);
+	if (!(&pdev->dev))
+		return ERR_PTR(-ENODEV);
+
+	regmap = regmap_init_mmio(&pdev->dev, base, &syscon_regmap_config);
 	if (IS_ERR(regmap)) {
 		pr_err("regmap init failed\n");
 		return ERR_CAST(regmap);
-------

I have tested this in linux-next and it works well. In this way there won't
be any issues of 
dereferencing NULL pointer in regmap.c and at the same time, if DT has
{big,little}-endian
optional property in syscon device node, it will be taken care.

So I would wait for Arnd's opinion about above mentioned changes and then
post a new
change after addressing Arnd's minor comment along with this fix in next
revision.


Thanks,
Pankaj Dubey
> Maybe we could consider create device structure for each syscon compatible
device in
> syscon driver in of_syscon_register in first time which seems to be
reasonable.
> 
> Regards
> Dong Aisheng
> 
> > --------------------------------------------
> > Subject: [PATCH] regmap: fix NULL pointer dereference in
> > regmap_get_val_endian
> >
> > Recent commits for getting reg endianess causing NULL pointer
> > dereference if dev is passed NULL in regmap_init_mmio. This patch
> > fixes this issue, and allows to parse reg endianess only if dev and
> > dev->of_node exist.
> >
> > Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
> > ---
> >  drivers/base/regmap/regmap.c |   23 ++++++++++++++---------
> >  1 file changed, 14 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/base/regmap/regmap.c
> > b/drivers/base/regmap/regmap.c index f2281af..455a877 100644
> > --- a/drivers/base/regmap/regmap.c
> > +++ b/drivers/base/regmap/regmap.c
> > @@ -477,7 +477,7 @@ static enum regmap_endian
> > regmap_get_val_endian(struct device *dev,
> >  					const struct regmap_bus *bus,
> >  					const struct regmap_config *config)
{
> > -	struct device_node *np = dev->of_node;
> > +	struct device_node *np;
> >  	enum regmap_endian endian;
> >
> >  	/* Retrieve the endianness specification from the regmap config */
> > @@ -487,15 +487,20 @@ static enum regmap_endian
> > regmap_get_val_endian(struct device *dev,
> >  	if (endian != REGMAP_ENDIAN_DEFAULT)
> >  		return endian;
> >
> > -	/* Parse the device's DT node for an endianness specification */
> > -	if (of_property_read_bool(np, "big-endian"))
> > -		endian = REGMAP_ENDIAN_BIG;
> > -	else if (of_property_read_bool(np, "little-endian"))
> > -		endian = REGMAP_ENDIAN_LITTLE;
> > +	/* If the dev and dev->of_node exist try to get endianness from DT
> > */
> > +	if (dev && dev->of_node) {
> > +		np = dev->of_node;
> >
> > -	/* If the endianness was specified in DT, use that */
> > -	if (endian != REGMAP_ENDIAN_DEFAULT)
> > -		return endian;
> > +		/* Parse the device's DT node for an endianness
> > specification */
> > +		if (of_property_read_bool(np, "big-endian"))
> > +			endian = REGMAP_ENDIAN_BIG;
> > +		else if (of_property_read_bool(np, "little-endian"))
> > +			endian = REGMAP_ENDIAN_LITTLE;
> > +
> > +		/* If the endianness was specified in DT, use that */
> > +		if (endian != REGMAP_ENDIAN_DEFAULT)
> > +			return endian;
> > +	}
> >
> >  	/* Retrieve the endianness specification from the bus config */
> >  	if (bus && bus->val_format_endian_default)
> > --
> >
> > Thanks,
> > Pankaj Dubey
> >
> > > Regards
> > > Dong Aisheng
> > >
> > > >
> > > > Thanks,
> > > > Pankaj Dubey
> > > >
> > > > > Regards
> > > > > Dong Aisheng
> > > > >
> > > > > >
> > > > > >
> > > > > > _______________________________________________
> > > > > > linux-arm-kernel mailing list
> > > > > > linux-arm-kernel@lists.infradead.org
> > > > > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> > > >
> >