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Date: Wed, 10 Oct 2018 10:14:28 +0900
From: "AKASHI, Takahiro" <takahiro.akashi@...aro.org>
To: Frank Rowand <frowand.list@...il.com>
Cc: Rob Herring <robh+dt@...nel.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>,
devicetree@...r.kernel.org
Subject: Re: [PATCH v15 06/16] of/fdt: add helper functions for handling
properties
Frank, Rob,
On Tue, Oct 09, 2018 at 10:47:15AM -0700, Frank Rowand wrote:
> On 10/08/18 17:37, AKASHI, Takahiro wrote:
> > On Fri, Oct 05, 2018 at 08:23:57AM -0500, Rob Herring wrote:
> >> 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.
> >
> > Okay, then I will leave this function, yet renaming it to
> > cpu64_to_fdt_cells() after Frank's comment.
>
> I have second guessed myself and do not like the name I suggested
> because what the function really does is either cpu32 to be32 or
> cpu64 to be64.
Okay.
> I agree with Rob that readability is important here. Instead of
> having a fill_property() function, how about having inline code,
> something like (untested even for thinkos):
>
> prop = buf;
>
> if (addr_cells == 1) {
> *(__be32 *)prop = cpu32_to_be32(addr);
> prop += 4;
> } else {
> *(__be64 *)prop = cpu64_to_be64(addr);
> prop += 8;
> }
>
> if (size_cells == 1)
> *(__be32 *)prop = cpu32_to_be32(size);
> else
> *(__be64 *)prop = cpu64_to_be64(size);
>
> You might want to also give Rob a chance to bike shed on this
> suggestion.
Basically, I don't care either way, but what Rob suggested
is that some architecture(s) might not handle correctly
unaligned memory access here.
I just want to stay tuned with Rob.
Thanks,
-Takahiro Akashi
> -Frank
>
> >
> > Thanks,
> > -Takahiro Akashi
> >>
> >> Rob
> >
>
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