From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH 1/2] of: base: Allow more args than MAX_PHANDLE_ARGS if required Date: Thu, 16 Jul 2015 11:23:26 +0100 Message-ID: <20150716102325.GC26390@arm.com> References: <1437035444-13867-1-git-send-email-joro@8bytes.org> <1437035444-13867-2-git-send-email-joro@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1437035444-13867-2-git-send-email-joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Joerg Roedel Cc: "grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org" , Rob Herring , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Joerg Roedel List-Id: devicetree@vger.kernel.org On Thu, Jul 16, 2015 at 09:30:43AM +0100, Joerg Roedel wrote: > From: Joerg Roedel > > The main use of MAX_PHANDLE_ARGS is to define the number of > args elements in 'struct of_phandle_args'. This struct is > often declared on the stack and thus it is impractical to > increase MAX_PHANDLE_ARGS again and again. > > To handle situations where more than MAX_PHANDLE_ARGS > elements may appear in a device-tree, introduce functions > to allocate/free 'struct of_phandle_args' with more than > MAX_PHANDLE_ARGS elements and provide the new function > of_parse_phandle_with_var_args(), which can handle those > variable-size structs. > > This is necessary for the ARM-SMMU driver, where the number > of mmu-masters can be up to 128. > > Signed-off-by: Joerg Roedel > --- > drivers/of/base.c | 43 ++++++++++++++++++++++++++++++++++++------- > include/linux/of.h | 7 +++++++ > 2 files changed, 43 insertions(+), 7 deletions(-) > > diff --git a/drivers/of/base.c b/drivers/of/base.c > index 8b5a187..2b288db 100644 > --- a/drivers/of/base.c > +++ b/drivers/of/base.c > @@ -54,6 +54,24 @@ DEFINE_MUTEX(of_mutex); > */ > DEFINE_RAW_SPINLOCK(devtree_lock); > > +struct of_phandle_args *of_alloc_phandle_args(int size) > +{ > + struct of_phandle_args *args; > + int e = max(0, size - MAX_PHANDLE_ARGS); > + > + args = kzalloc(sizeof(struct of_phandle_args) + e * sizeof(uint32_t), > + GFP_KERNEL); Should you also update args->args_count to reflect the extended array? That said, extending the fixed-size array member like this feels a bit fragile. Does GCC not complain about out-of-bounds accesses if you statically address args->args[MAX_PHANDLE_ARGS]? Admittedly, I can't think *why* this would be break (things like additional padding will be harmless), but I'm not intimate with the C standard. I guess the more worrying possibility is if somebody adds a new member to the end of of_phandle_args. Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html