devicetree.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Geert Uytterhoeven <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>
To: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
Cc: "Frank Rowand"
	<frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"Rob Herring" <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	"Devicetree Compiler"
	<devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"devicetree-spec-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<devicetree-spec-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"Jon Loeliger" <jdl-CYoMK+44s/E@public.gmane.org>,
	"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"Pantelis Antoniou"
	<pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>,
	"Pantelis
	Antomarek.vasut-Re5JQEeQqe/2sr8fMPgRzw@public.gmane.org"
	<panto-wVdstyuyKrO8r51toPun2/C9HSW9iNxf@public.gmane.org>,
	"Grant Likely"
	<grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>,
	"Marek Vašut"
	<marek.vasut-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"Tom Rini" <trini-OWPKS81ov/FWk0Htik3J/w@public.gmane.org>,
	"Kyle Evans" <kevans-h+KGxgPPiopAfugRpC6u6w@public.gmane.org>,
	"Alan Tull" <atull-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	"Michael Ellerman" <mpe-Gsx/Oe8HsFggBc27wqDAHg@public.gmane.org>
Subject: Re: [RFC] devicetree: new FDT format version
Date: Fri, 26 Jan 2018 09:56:21 +0100	[thread overview]
Message-ID: <CAMuHMdV0jdj90uzqMx_wtvz=-KaagJG2_UQTm1DW3gzt6cNG6A@mail.gmail.com> (raw)
In-Reply-To: <20180125122912.GB2099@umbus>

On Thu, Jan 25, 2018 at 1:29 PM, David Gibson
<david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org> wrote:
> On Wed, Jan 24, 2018 at 04:22:15PM -0800, Frank Rowand wrote:
>> On 01/24/18 13:16, Frank Rowand wrote:
>> > What you say makes sense.  So I'll reverse myself and say that for
>> > Linux, we should update the FDT read code to scan all chained
>> > overlay FDT(s) as well as the base FDT.
>>
>> < snip >
>>
>> What I wrote was somewhat ambiguous.  What I meant by "FDT read
>> code" was functions that check for existence of nodes in the
>> FDT or read property values from the FDT.
>
> Oh.. not just FDT unflattening code.
>
> The trouble with this is that scanning for a specific node or property
> in a set of chained overlays is highly nontrivial.  Even if you set
> aside the arguably self-imposed design constraints in libfdt, you
> can't just do the same lookup in each fragment: along the way you need
> to resolve the path at which each fragment applies.  That in itself is
> non-trivial.  If you have overlays applying on top of other overlays,
> that could involve recursive lookups of things from previous overlays.
> It's spectacularly complicated and we have to do it on *every single*
> read operation.
>
> Either fully applying the overlay in flattened form, or (even

Applying the overlays in flattened form sounds like a good idea to me.
It still adds complexity, but handling multiple overlays can be done by a
simple iteration, not recursion.
The end result will always consume less memory, and will thus fit in the
original block of memory allocated for base FDT and overlay FDTs, unless
the base FDT and overlay FDTs are in FLASH (this assumes chaining really
means appending, not using an external chaining mechanism).

> temporarily) unflattening the tree are better solutions.

Temporary unflattening sounds like a waste to me: it must be redone again
later anyway. Applying the FDT overlays early on will make that later step
simpler (no more overlays to handle).
So if you need information from an FDT, you can help later steps by
applying the FDT overlays right away.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

  parent reply	other threads:[~2018-01-26  8:56 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-22  8:09 Frank Rowand
     [not found] ` <b96829f9-2e8b-fdc5-5090-58591e2260cf-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-22  8:14   ` Frank Rowand
     [not found]     ` <ec68cfb3-4702-ba00-e926-3ad63b20b199-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-22 20:08       ` Frank Rowand
2018-01-22 20:08   ` Frank Rowand
     [not found]     ` <bc44f051-835d-1c8d-a928-be0fd4ef80b5-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-25  0:27       ` Frank Rowand
     [not found]         ` <b5a72db1-45b2-f21f-9afd-0991b288840e-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-27  8:48           ` David Gibson
2018-01-29  8:08             ` Frank Rowand
     [not found]               ` <2c352396-154e-ea75-c50b-0f2bfafd19da-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-29 10:56                 ` David Gibson
2018-01-30  1:29                   ` Frank Rowand
2018-01-22 21:01   ` Rob Herring
     [not found]     ` <CAL_JsqJR2y7bMw_-9TBAGWZ_kf7_sZo5qvqvRowJ8jiy=4G0Bg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-01-23 12:42       ` David Gibson
2018-01-23 21:17         ` Frank Rowand
     [not found]           ` <20328477-e511-e875-7dc4-253640f2219e-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-24 15:47             ` Rob Herring
     [not found]               ` <CAL_Jsq+fvFrGhqO0zbEUE_i23FkU=G4Z1-e0vnXHi4KbS2oK0A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-01-24 21:16                 ` Frank Rowand
     [not found]                   ` <e1bec77d-4dac-200b-34be-23573bf738f0-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-24 22:27                     ` Alan Tull
2018-01-25  0:22                     ` Frank Rowand
     [not found]                       ` <e986435b-481b-2629-7600-10d9e21ac58e-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-25 12:29                         ` David Gibson
2018-01-25 20:01                           ` Frank Rowand
     [not found]                             ` <72d30756-a963-92c9-1838-3e3f80c57e39-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-29 18:32                               ` Grant Likely
     [not found]                                 ` <CACxGe6tUB3NhNhOtqzoJfThx=RE1_=TSDQz+wQUm=sdE5JirZQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-01-29 23:15                                   ` David Gibson
2018-01-26  8:56                           ` Geert Uytterhoeven [this message]
     [not found]                             ` <CAMuHMdV0jdj90uzqMx_wtvz=-KaagJG2_UQTm1DW3gzt6cNG6A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-01-26  8:59                               ` Geert Uytterhoeven
2018-01-26 22:08                               ` Frank Rowand
     [not found]                                 ` <83008da0-7383-ba2d-a239-e11ad7d1327d-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-27  9:00                                   ` David Gibson
2018-01-27  8:56                               ` David Gibson
2018-01-25 23:11                     ` Frank Rowand
2018-01-25 12:22                 ` David Gibson
2018-01-25  9:14             ` Marek Vasut
     [not found]               ` <90983180-ae3b-5a31-9dc0-b62b978a0fba-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-25 12:37                 ` David Gibson
2018-01-27 20:30                   ` Marek Vasut
     [not found]                     ` <5a943937-3b59-514b-3939-df25daea5470-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-01-29  0:53                       ` David Gibson
2018-01-23 12:05   ` David Gibson
2018-01-23 21:28     ` Frank Rowand

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAMuHMdV0jdj90uzqMx_wtvz=-KaagJG2_UQTm1DW3gzt6cNG6A@mail.gmail.com' \
    --to=geert-td1emuhucqxl1znqvxdv9g@public.gmane.org \
    --cc=atull-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org \
    --cc=david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org \
    --cc=devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --cc=devicetree-spec-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --cc=devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --cc=frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
    --cc=grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org \
    --cc=jdl-CYoMK+44s/E@public.gmane.org \
    --cc=kevans-h+KGxgPPiopAfugRpC6u6w@public.gmane.org \
    --cc=marek.vasut-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org \
    --cc=mpe-Gsx/Oe8HsFggBc27wqDAHg@public.gmane.org \
    --cc=pantelis.antoniou-OWPKS81ov/FWk0Htik3J/w@public.gmane.org \
    --cc=panto-wVdstyuyKrO8r51toPun2/C9HSW9iNxf@public.gmane.org \
    --cc=robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org \
    --cc=trini-OWPKS81ov/FWk0Htik3J/w@public.gmane.org \
    --subject='Re: [RFC] devicetree: new FDT format version' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox