linux-kernel - Re: [PATCH v15 06/16] of/fdt: add helper functions for handling properties

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Date:   Fri, 5 Oct 2018 08:23:57 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Howells <dhowells@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>, dyoung@...hat.com,
        Baoquan He <bhe@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        prudo@...ux.ibm.com, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        James Morse <james.morse@....com>, bhsharma@...hat.com,
        kexec@...ts.infradead.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v15 06/16] of/fdt: add helper functions for handling properties

On Thu, Oct 4, 2018 at 10:07 PM AKASHI, Takahiro
<takahiro.akashi@...aro.org> wrote:
>
> Rob,
>
> # I haven't replied to this comment yet.
>
> On Fri, Sep 28, 2018 at 08:44:42AM -0500, Rob Herring wrote:
> > +David Gibson
> >
> > On Fri, Sep 28, 2018 at 1:48 AM AKASHI Takahiro
> > <takahiro.akashi@...aro.org> wrote:
> > >
> > > These functions will be used later to handle kexec-specific properties
> > > in arm64's kexec_file implementation.
> > >
> > > Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> > > Cc: Rob Herring <robh+dt@...nel.org>
> > > Cc: Frank Rowand <frowand.list@...il.com>
> > > Cc: devicetree@...r.kernel.org
> > > ---
> > >  drivers/of/fdt.c       | 56 ++++++++++++++++++++++++++++++++++++++++++
> > >  include/linux/of_fdt.h |  4 +++
> > >  2 files changed, 60 insertions(+)
> > >
> > > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > > index 800ad252cf9c..c65c31562ccb 100644
> > > --- a/drivers/of/fdt.c
> > > +++ b/drivers/of/fdt.c
> > > @@ -25,6 +25,7 @@
> > >  #include <linux/debugfs.h>
> > >  #include <linux/serial_core.h>
> > >  #include <linux/sysfs.h>
> > > +#include <linux/types.h>
> > >
> > >  #include <asm/setup.h>  /* for COMMAND_LINE_SIZE */
> > >  #include <asm/page.h>
> > > @@ -1323,3 +1324,58 @@ late_initcall(of_fdt_raw_init);
> > >  #endif
> > >
> > >  #endif /* CONFIG_OF_EARLY_FLATTREE */
> > > +
> > > +#define FDT_ALIGN(x, a)        (((x) + (a) - 1) & ~((a) - 1))
> > > +#define FDT_TAGALIGN(x)        (FDT_ALIGN((x), FDT_TAGSIZE))
> > > +
> > > +int fdt_prop_len(const char *prop_name, int len)
> > > +{
> > > +       return (strlen(prop_name) + 1) +
> > > +               sizeof(struct fdt_property) +
> > > +               FDT_TAGALIGN(len);
> >
> > Looks like you are using this to calculate how much space you need to
> > allocate in addition to the current DTB for a couple of new or
> > replaced properties. I'm not sure that this calculation is completely
> > accurate. And it is strange there doesn't seem to be any libfdt
> > function for this already. It would be simpler to just add some fixed
> > additional amount.
> >
> > Maybe David G has comments on this?
> >
> > > +}
> > > +
> >
> > The rest of this should go in drivers/of/fdt_address.c. Ultimately, it
> > should go into libfdt, but I'm fine with having it in the kernel for
> > now.
>
> I'd like to have this function in the kernel for now.
>
> > > +static void fill_property(void *buf, u64 val64, int cells)
> > > +{
> > > +       __be32 val32;
> > > +
> > > +       while (cells) {
> > > +               val32 = cpu_to_fdt32((val64 >> (32 * (--cells))) & U32_MAX);
> > > +               memcpy(buf, &val32, sizeof(val32));
> > > +               buf += sizeof(val32);
> >
> > This is kind of hard to read. I would copy u-boot's fdt_pack_reg function.
>
> Are you sure?
> I originally implemented this function in a similar way that fdt_pack_reg()
> was, but, you suggested, in your past comment[1], that we'd be better to
> have of_read_number()-like implementation.
>
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/579118.html

Yeah, you're right. Plus, I'm not sure the u-boot one would work for
unaligned accesses with armv5 and earlier h/w.

My only comment then is I think you can drop the U32_MAX masking.

Rob