Re: [PATCH v2 3/3] powerpc: Add support for ram filesystems in FIT uImages

[Grant Likely <grant.likely@secretlab.ca>]

On Fri, Jan 1, 2010 at 7:12 AM, Wolfgang Denk <wd@denx.de> wrote:
> Dear Grant,
>
> In message <fa686aa40912301601s6cd0ec4y85b88976159a36af@mail.gmail.com> you wrote:
>>
>> Thinking further, I do actually have another concern, at least with
>> regard to the way the current patch set implements things.  Is it
>> expected or even "recommended" that fit images will *always* contain a
>> .dtb image?  The current patch only handles the case of a .dtb
>> embedded inside the fit image.
>
> I think this can be expected.
>
> Historically, the need to pass the dtb image to the Linux kernel,
> too, was what actually triggered the development of the FIT image
> format, as it turned out that the old image format with it's fixed
> binary header was too inflexible. So bundling the kernel image and
> the device tree blob into one image file is the specific use case
> this image format was created for (which does not mean that other
> usage would be impossible).
>
>> Personally, I don't get any benefit out of the new image format, so I
>> haven't spent any time looking at it.  However, I'm concerned about
>
> Assume you want to boot over DHCP or similar, where you can provide
> just a single image file for download. Here it is definitely nice if
> you can bundle the kernel image and the DTB into one image file. We
> were able to extend the old so-called "multi-file" uImage format to
> handle this situation, too, but it was clear that further extensions
> were not really possible.
>
> We consider the old legace uImage format as something we want to move
> away from, and the new FIT image format shall be the new default.
>
>> the drift back towards a different image per target when the move over
>> the last 4 years has been towards multiplatform kernel images.  I
>> certainly don't want to encourage embedding the device tree blob into
>> the kernel image, and I'm not very interested in merging code to do
>> that into the kernel tree.  If someone really needs to do that for
>> their particular target, it is certainly easy enough for them to weld
>> in the .dtb after the fact before transferring the image to the
>> target, but I want that mode to be the exception, not the rule.
>
> This is specific for particular targets, but for  specific  modes  of
> operation,  like  booting  over  the network or other szenarios where
> transferring a single image file is essential - another example where
> we often see this request is upgrade procedures for devics, where the
> vendor wants to be able to distribute a single file  for  his  target
> systems   to  avoid  customers  bricking  their  devices  by  chosing
> incompatible combinations.

As I said in a previous email; I understand the need for certain
scenarios, but in the general case it is not the mode that I think
should be encouraged.  I don't want to merge additional targets for
.dtb embedded in the kernel image unless absolutely necessary, and I
want developers to have the mindset that .dtbs should be separate from
the kernel; and should be quasi-stable (or at least more stable than
the kernel itself) because I think that multiplatform is important,
and is going to become more important in the future.

So I don't want to support it by default; but OTOH, I'm not going to
actively prevent embedded .dtb blobs either.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.