From: Joel A Fernandes <agnel.joel@gmail.com>
To: Pantelis Antoniou <panto@antoniou-consulting.com>
Cc: Grant Likely <grant.likely@secretlab.ca>,
Rob Herring <robherring2@gmail.com>,
Deepak Saxena <dsaxena@linaro.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Scott Wood <scottwood@freescale.com>,
Tony Lindgren <tony@atomide.com>, Russ Dill <Russ.Dill@ti.com>,
Felipe Balbi <balbi@ti.com>, Benoit Cousson <b-cousson@ti.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Koen Kooi <koen@dominion.thruhere.net>,
Matt Porter <mporter@ti.com>,
linux-omap@vger.kernel.org, Kevin Hilman <khilman@ti.com>,
Paul Walmsley <paul@pwsan.com>,
devicetree-discuss@lists.ozlabs.org
Subject: Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2)
Date: Fri, 9 Nov 2012 21:36:26 -0600 [thread overview]
Message-ID: <CAD=GYpZwpRRUD=Qy529KkiL-5e2zHaCWMZM9+CTQEnMqSR3yEw@mail.gmail.com> (raw)
In-Reply-To: <559B8433-67C3-4A1A-A5D6-859907655176@antoniou-consulting.com>
Hi Pantelis,
On Fri, Nov 9, 2012 at 2:13 AM, Pantelis Antoniou
<panto@antoniou-consulting.com> wrote:
>>>> Option C: U-Boot loads both the base and overlay FDT files, merges them,
>>>> and passes the resolved tree to the kernel.
>>>>
>>>
>>> Could be made to work. Only really required if Joanne wants the
>>> cape interface to work for u-boot too. For example if the cape has some
>>> kind of network interface that u-boot will use to boot from.
>>>
>>
>> I love Grant's hashing idea a lot keeping the phandle problem for
>> compile time and not requiring fixups.
>>
>> IMO it is still a cleaner approach if u-boot does the tree merging for
>> all cases, and not the kernel.
>>
>> That way from a development standpoint, very little or nothing will
>> have to be changed in kernel (except for scripts/dtc) considering we
>> are moving forward with hashing.
>>
>> Also this discussed a while back but at some point is going to brought
>> up again- loading of dt fragment directly from EEPROM and merging at
>> run time. If we were to implement this in kernel, we would have to add
>> cape specific EEPROM reading code, merge the tree before it is
>> unflattened and parse. I think doing tree merging in kernel is messy
>> and we should do it in uboot. Ideally reading the fragment from the
>> EEPROM for all capes and merging without worrying about version
>> detection, Doing the merge and passing the merged blob to the kernel
>> which (kernel) works the same way it does today.
>
> Not going to work, for a lot of cases. Doing it in the kernel seems to be
> the cleaner option. There are valid use cases for doing in u-boot too.
True, if dynamic runtime stuff from userspace is what we're talking
about, then yeah I see the important need for kernel to do the merge.
>> Alternatively to hashing, reading david gibsons paper I followed,
>> phandle is supposed to 'uniquely' identity node. I wonder why the node
>> name itself is not sufficient to unquiely identify. The code that does
>> the tree walking can then just strcmp the node name while it walks the
>> tree instead of having to find a node with a phandle number. I guess
>> the reason is phandles are small to store as data values. Another
>> approach can be to arrange the string block in alphabetical order
>> (unless it already is), and store phandle as index of the node name
>> referenced relative to the starting of the strong block. This will not
>> affect nodes in dtb being moved around since they will still have the
>> same index value. the problem being adding or removing nodes Changes
>> the offsets of all other nodes in the string block as well.. Hmm.
>>
>
> This is pretty radical change to the DT format, no?
Yes, true and the only way hypothetically to replace the phandle
tree-walking mechanism is to store node paths instead of phandle which
David pointed is too long to store, so I guess this wont work after
all. Anyway this was an interesting exercise, thanks.
Regards,
Joel
next prev parent reply other threads:[~2012-11-10 3:36 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-05 20:40 [RFC] Device Tree Overlays Proposal (Was Re: capebus moving omap_devices to mach-omap2) Grant Likely
2012-11-05 21:40 ` Tabi Timur-B04825
2012-11-05 23:22 ` Tony Lindgren
2012-11-09 12:06 ` Grant Likely
2012-11-06 0:07 ` Grant Likely
2012-11-06 10:31 ` Pantelis Antoniou
2012-11-07 22:35 ` Ryan Mallon
2012-11-08 13:28 ` Koen Kooi
2012-11-08 14:09 ` Timur Tabi
2012-11-08 17:00 ` Mitch Bradley
2012-11-06 10:30 ` Pantelis Antoniou
2012-11-06 11:14 ` Grant Likely
2012-11-06 18:35 ` Tony Lindgren
2012-11-06 19:29 ` Russ Dill
2012-11-06 19:41 ` Pantelis Antoniou
2012-11-06 22:17 ` Stephen Warren
2012-11-06 19:34 ` Pantelis Antoniou
2012-11-06 20:45 ` Grant Likely
2012-11-06 20:50 ` Grant Likely
2012-11-07 8:06 ` Pantelis Antoniou
2012-11-07 15:33 ` Alan Tull
2012-11-09 17:03 ` Grant Likely
2012-11-07 8:13 ` Pantelis Antoniou
2012-11-07 10:19 ` Benoit Cousson
2012-11-07 11:02 ` Pantelis Antoniou
2012-11-07 11:12 ` Benoit Cousson
2012-11-07 11:23 ` Pantelis Antoniou
2012-11-09 20:33 ` Grant Likely
2012-11-12 11:34 ` Pantelis Antoniou
2012-11-12 13:01 ` Grant Likely
2012-11-07 17:25 ` Stephen Warren
2012-11-07 22:10 ` Pantelis Antoniou
2012-11-08 10:36 ` Cousson, Benoit
2012-11-09 5:32 ` Joel A Fernandes
2012-11-09 14:29 ` David Gibson
2012-11-10 3:15 ` Joel A Fernandes
2012-11-09 21:22 ` Grant Likely
2012-11-12 11:47 ` Pantelis Antoniou
2012-11-13 3:59 ` Joel A Fernandes
2012-11-09 22:59 ` Stephen Warren
[not found] ` <-4237940489086529028@unknownmsgid>
[not found] ` <559B8433-67C3-4A1A-A5D6-859907655176@antoniou-consulting.com>
2012-11-10 3:36 ` Joel A Fernandes [this message]
2012-11-12 12:48 ` Pantelis Antoniou
2012-11-13 2:28 ` David Gibson
2012-11-06 22:37 ` Stephen Warren
2012-11-07 0:54 ` Mitch Bradley
2012-11-09 17:02 ` Grant Likely
2012-11-12 11:29 ` Pantelis Antoniou
2012-11-07 8:47 ` Pantelis Antoniou
2012-11-07 17:18 ` Stephen Warren
2012-11-07 22:08 ` Pantelis Antoniou
2012-11-09 16:28 ` Grant Likely
2012-11-09 23:23 ` Stephen Warren
2012-11-09 23:40 ` Grant Likely
2012-11-12 10:53 ` Koen Kooi
2012-11-12 12:10 ` Pantelis Antoniou
2012-11-12 16:52 ` Stephen Warren
2012-11-13 7:25 ` David Gibson
2012-11-13 8:09 ` Pantelis Antoniou
2012-11-13 12:24 ` Grant Likely
2012-11-13 13:38 ` Pantelis Antoniou
2012-11-15 4:57 ` David Gibson
2012-11-13 17:10 ` Stephen Warren
2012-11-13 23:30 ` David Gibson
2012-11-14 0:00 ` Pantelis Antoniou
2012-11-13 16:57 ` Stephen Warren
2012-11-13 18:10 ` Mitch Bradley
2012-11-13 18:29 ` Stephen Warren
2012-11-13 19:09 ` Mitch Bradley
2012-11-13 19:11 ` Pantelis Antoniou
2012-11-17 22:27 ` Jean-Christophe PLAGNIOL-VILLARD
2012-11-20 17:09 ` Grant Likely
2012-11-11 20:47 ` Rob Landley
2012-11-12 12:50 ` Pantelis Antoniou
2012-11-12 16:54 ` Stephen Warren
2012-11-12 11:23 ` Pantelis Antoniou
2012-11-12 16:49 ` Stephen Warren
2012-11-12 17:00 ` Pantelis Antoniou
2012-11-12 17:10 ` Stephen Warren
2012-11-12 17:19 ` Pantelis Antoniou
2012-11-12 17:29 ` Stephen Warren
2012-11-12 17:38 ` Pantelis Antoniou
2012-11-12 20:16 ` Russ Dill
2012-11-12 16:45 ` Stephen Warren
2012-11-09 2:26 ` David Gibson
2012-11-09 15:40 ` Pantelis Antoniou
2012-11-13 0:03 ` David Gibson
2012-11-09 21:08 ` Grant Likely
2012-11-13 0:05 ` David Gibson
2012-11-09 21:42 ` Grant Likely
2012-11-13 1:05 ` David Gibson
2012-11-13 5:22 ` Stephen Warren
2012-11-13 6:54 ` David Gibson
2012-11-09 22:57 ` Stephen Warren
2012-11-09 23:27 ` Grant Likely
2012-11-12 12:05 ` Pantelis Antoniou
2012-11-09 23:14 ` Stephen Warren
2012-11-09 23:06 ` Stephen Warren
2012-11-09 23:32 ` Grant Likely
2012-11-12 11:03 ` Koen Kooi
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