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

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Message-ID: <20181002044710.GD1886@umbus.fritz.box>
Date:   Tue, 2 Oct 2018 14:47:10 +1000
From:   David Gibson <david@...son.dropbear.id.au>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        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 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?

Hrm.  Yeah, the approach I'd suggest would be to just add a fixed
amount, and if your functions return -FDT_ERR_NOSPACE, add some more.
That's pretty much the expected way of working with fdts in write
mode.

If that's really not suitable, we could look at adding a helper to
estimate this in libfdt.  Or, actually, I suspect taking an existing
libfdt internal helper, polishing and exporting it.

> 
> > +}
> > +
> 
> 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.
> 
> > +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.
> 
> BTW, for purposes of moving to libfdt, we'll need the authors'
> (Masahiro Yamada and Hans de Goede) permission to dual license.
> 
> > +       }
> > +}
> > +
> > +int fdt_setprop_reg(void *fdt, int nodeoffset, const char *name,
> > +                                               u64 addr, u64 size)
> > +{
> > +       int addr_cells, size_cells;
> > +       char buf[sizeof(__be32) * 2 * 2];
> > +               /* assume dt_root_[addr|size]_cells <= 2 */
> > +       void *prop;
> > +       size_t buf_size;
> > +
> > +       addr_cells = fdt_address_cells(fdt, 0);
> > +       if (addr_cells < 0)
> > +               return addr_cells;
> > +       size_cells = fdt_size_cells(fdt, 0);
> > +       if (size_cells < 0)
> > +               return size_cells;
> > +
> > +       /* if *_cells >= 2, cells can hold 64-bit values anyway */
> > +       if ((addr_cells == 1) && (addr > U32_MAX))
> > +               return -FDT_ERR_BADVALUE;
> > +
> > +       if ((size_cells == 1) && (size > U32_MAX))
> > +               return -FDT_ERR_BADVALUE;
> > +
> > +       buf_size = (addr_cells + size_cells) * sizeof(u32);
> > +       prop = buf;
> > +
> > +       fill_property(prop, addr, addr_cells);
> > +       prop += addr_cells * sizeof(u32);
> > +
> > +       fill_property(prop, size, size_cells);
> > +
> > +       return fdt_setprop(fdt, nodeoffset, name, buf, buf_size);
> > +}
> > diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
> > index b9cd9ebdf9b9..842af6ea92ea 100644
> > --- a/include/linux/of_fdt.h
> > +++ b/include/linux/of_fdt.h
> > @@ -108,5 +108,9 @@ static inline void unflatten_device_tree(void) {}
> >  static inline void unflatten_and_copy_device_tree(void) {}
> >  #endif /* CONFIG_OF_EARLY_FLATTREE */
> >
> > +int fdt_prop_len(const char *prop_name, int len);
> > +int fdt_setprop_reg(void *fdt, int nodeoffset, const char *name,
> > +                                               u64 addr, u64 size);
> > +
> >  #endif /* __ASSEMBLY__ */
> >  #endif /* _LINUX_OF_FDT_H */
> >
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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