[OpenWrt-Devel] [PATCH v1 0/7] Add custom TRX header option

[Florian Fainelli]

On 09/02/15 13:12, Will Sheppard wrote:
> Hi - thanks for review; reply inline
> 
> On 9 February 2015 at 20:52, Florian Fainelli <florian at openwrt.org
> <mailto:florian at openwrt.org>> wrote:
> 
>     On 09/02/15 08:29, Will Sheppard wrote:
>     > Patchset to essentially add custom TRX header to all firmware produced.
>     >
>     > This is most useful for the Belkin routers from my experience. I'm not
>     > how other trx based firmwares modify the header for their own purposes.
>     >
>     > This is applied across the board so that the kernel, trx tools and mtd
>     > tools are all compiled with the specified header.
>     >
>     > I have modified the kernel specifically for the brcm47xx based boards to
>     > ensure the mtd parser looks for the correct magic. NOTE: This function will,
>     > for other boards, fail.
> 
>     I don't think this is desirable at all to have, for many reasons:
> 
>     - how can an use figure out the proper TRX_MAGIC value he/she should
>     use?
> 
> 
> There's simply no hard-and-fast rule for this - just looking at a
> factory binary might not help - it worked for me. 

That was more of a rhetorical question, since this is not easy, someone
has to do it, and preferably in a way that makes the build reliable for
end-users.

> 
> 
>     - this is extremely error prone and can result, as you mention in
>     failing to work with existing devices with well-defined TRX headers
> 
> 
> Error prone inasmuch as it could be the wrong value and thus brick the
> router? ( I guess I'm always thinking from a "have a serial port"
> perspective ) 

Error prone on multiple levels: what happens if I wipe-out my original
config and can't remember the correct 32-bits magic value? What if the
option is renamed, what I upgrade the kernel but not mtd, etc...

> 
> 
>     - how can we get some level of reproducibility for both the kernel and
>     firmware tools builds?
> 
>     I would really encourage you to extend the existing code to take an
>     arbitrary list of TRX magics, such that you can have maybe a single file
>     to modify and both "mtd" and the kernel can use that list of magic
>     values accordingly.
> 
> 
> I agree. As the mtd utility looks for this value though, it would have
> to know what router it was being used on - i'm not sure that is
> available as a value in user-space is it?

You can certainly extract the board you are running on, but that assumes
you already have a working user-space and kernel, hence the partition
parser needs to work etc... chicken and egg. The alternative, which is
likely what is happening today, is that you need to flash a special
image, with a special magic that only supports a particular set of
boards using a defined TRX magic value, that way you can become (at
least at the MTD level) board agnostic.

> 
> 
>     Out of curiosity, how many different TRX magic values should we have to
>     support with or without your patches?
> 
> 
> I know that Belkin seem to use different magics i.e. not HDR0, I'm not
> sure about other manufacturers. But presumably these values could be
> added as they become known.

That is the direction I would take, just add them one by one such that
you can control exactly when both user-space and kernel space can
properly support a given model (or family of).

> 
> 
>     >
>     > Will Sheppard (7):
>     >   config: Add option to specify custom TRX header
>     >   mtd: Add custom trx magic option to mtd tool
>     >   mtd: Fix: Use TRX_MAGIC define not hard-coded number
>     >   trx: Add custom TRX option to trx firmware tool
>     >   mtd: Add debug showing header magic in use
>     >   kernel: bcm47xx: Add custom TRX header option to kernel
>     >   mtd: Fix makefile to work with quilt as per wiki
>     >
>     >  config/Config-images.in                            | 15 ++++++++++
>     >  package/system/mtd/Makefile                        |  9 +++++-
>     >  package/system/mtd/src/trx.c                       | 10 +++++--
>     >  .../patches-3.14/162-Belkin_custom_trx_magic.patch | 35
>     ++++++++++++++++++++++
>     >  tools/firmware-utils/Makefile                      |  4 +++
>     >  tools/firmware-utils/src/trx.c                     | 10 ++++++-
>     >  6 files changed, 79 insertions(+), 4 deletions(-)
>     >  create mode 100644
>     target/linux/brcm47xx/patches-3.14/162-Belkin_custom_trx_magic.patch
>     >
> 
> 
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