From: Timur Tabi <timur@freescale•com>
To: Grant Likely <grant.likely@secretlab•ca>
Cc: linuxppc-dev@ozlabs•org, devicetree-discuss@lists•ozlabs.org
Subject: Re: [PATCH] powerpc/fsl: add device tree binding for QE firmware
Date: Wed, 24 Mar 2010 12:31:54 -0500 [thread overview]
Message-ID: <4BAA4C8A.70104@freescale.com> (raw)
In-Reply-To: <fa686aa41003241007mf6052d5s4643795f4a87cdcf@mail.gmail.com>
Grant Likely wrote:
> On Wed, Mar 24, 2010 at 11:00 AM, Segher Boessenkool
> <segher@kernel•crashing.org> wrote:
>>>> Why the phandle redirection? Why not just put the firmware blob into
>>>> a property in the QE node, or as a subnode?
>>>
>>> Because there might be multiple QE devices on a single chip, and each
>>> will need to upload the same firmware. So instead of embedding the
>>> firmware multiple times, just embed it once, and have a pointer.
>>
>> You're messing up the binding because of a (perceived) deficiency in
>> the DTB format?
Huh? Who says anything about messing up? I don't see anything "messed up" about including a blob of data with proper compatible properties, etc.
>> Or maybe just the DTS format. Or maybe you shouldn't
>> even care about size here. Or really, the device tree is the wrong
>> place to store firmware blobs at all.
>
> That is a good question. Why is it necessary to pass the blob via the
> tree?
Because sometimes the firmware is needed before networking or serial I/O can function. Today, we do one of two things on systems with QE (or QE-like microcontrollers):
1) U-Boot uploads the firmware, and may create a DTB node that provides some information about the firmware.
2) U-Boot uploads the firmware, but then gives Linux the physical address (in flash) of the firmware so that it can upload it again.
> So far we've avoided using firmware blobs in the flat trees.
> Or to ask in other words; what is the use case that requires passing
> via the device tree?
The Fman devices on the Freescale P4080 needs to have the firmware uploaded by the kernel before they will function. I can't depend on having the firmware on the root file system, and we can't embed it in the kernel itself (because it's proprietary), so where else should I put it? Today, we just leave it in flash and give the physical address to the Fman Linux driver via a command-line parameter. But that doesn't work because then it means we have to have flash mapped to every partition that runs Linux.
> Also, depending on firmware to correctly squirt the firmware blob into
> the dtb at boot is risky. Even when firmware is buggy, there is
> resistance to upgrading firmware on working boards because it could
> result in a bricked board.
I'm not sure what you're getting at. This has nothing to do with upgrading firmware. The firmware is already in flash, I just need a better way of giving it to the kernel. If you upgrade the firmware in flash, then U-Boot will automatically provide the new version to the kernel via the DTB. I just don't see how upgrading is a factor.
> In fact, every time we depend on firmware
> to modify the dtb at boot is risky, so it should only be done when
> strictly necessary (I would even say that to date we've probably been
> rather too liberal about getting u-boot to modify the device tree).
Embedding the firmware blob in the DTS is uglier than having U-Boot do it, IMHO.
> I would say that either the firmware should be loaded via the existing
> (non-dt) firmware loading mechanism,
That, unfortunately, is not an option.
> or it should be built into the
> static dtb blob. Don't try to add it at runtime.
Then how do I distribute the firmware blob? It's not GPL, so it can't go into arch/powerpc/boot/dts/. Are you suggesting I do this in the DTS:
/ {
model = "MPC8323EMDS";
compatible = "MPC8323EMDS", "MPC832xMDS", "MPC83xxMDS";
#address-cells = <1>;
#size-cells = <1>;
...
qe_firmware:qe-firmware {
compatible = "fsl,qe-firmware";
fsl,firmware = <0x70 0xcd 0x00 0x00 0x01 0x46 0x45 0x63 ...>
}
}
Most firmware is 8-12KB, so this will make for one ugly DTS. Plus, there's the issue of distributing non-GPL firmware data inside a DTS, which is GPL.
--
Timur Tabi
Linux kernel developer at Freescale
next prev parent reply other threads:[~2010-03-24 17:31 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-23 21:42 [PATCH] powerpc/fsl: add device tree binding for QE firmware Timur Tabi
2010-03-24 6:07 ` Grant Likely
2010-03-24 12:05 ` Timur Tabi
2010-03-24 17:00 ` Segher Boessenkool
2010-03-24 17:07 ` Grant Likely
2010-03-24 17:31 ` Timur Tabi [this message]
2010-03-24 18:10 ` Grant Likely
2010-03-24 18:21 ` Mitch Bradley
2010-03-24 18:25 ` Timur Tabi
2010-03-24 18:24 ` M. Warner Losh
2010-03-24 18:31 ` Timur Tabi
2010-03-25 1:49 ` Segher Boessenkool
2010-03-25 14:42 ` Timur Tabi
2010-03-25 16:10 ` Grant Likely
2010-03-25 16:34 ` Scott Wood
2010-03-25 16:46 ` Timur Tabi
2010-03-26 18:23 ` Rafal Jaworowski
2010-03-25 23:53 ` M. Warner Losh
2010-03-26 0:22 ` Timur Tabi
2010-03-25 15:16 ` Scott Wood
2010-03-25 15:29 ` Mitch Bradley
2010-03-25 16:16 ` Grant Likely
2010-03-25 16:36 ` Timur Tabi
2010-03-25 16:50 ` Scott Wood
2010-03-25 16:59 ` Grant Likely
2010-03-25 17:03 ` Timur Tabi
2010-03-25 17:35 ` Grant Likely
2010-03-25 18:05 ` Timur Tabi
2010-03-25 19:53 ` Scott Wood
2010-03-25 20:04 ` Timur Tabi
2010-03-25 21:54 ` Grant Likely
2010-03-25 22:19 ` Timur Tabi
2010-03-25 21:39 ` Grant Likely
2010-03-25 22:47 ` Scott Wood
2010-03-25 21:22 ` David Gibson
2010-03-26 1:26 ` Grant Likely
2010-03-26 15:17 ` Timur Tabi
2010-03-26 18:20 ` Grant Likely
2010-03-26 18:39 ` Timur Tabi
2010-03-26 18:44 ` Grant Likely
2010-03-26 18:48 ` Timur Tabi
2010-03-26 18:56 ` Grant Likely
2010-03-26 18:58 ` Mitch Bradley
2010-03-26 19:07 ` Grant Likely
2010-03-26 18:48 ` Mitch Bradley
2010-03-24 18:27 ` Scott Wood
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