[U-Boot] [PATCH 3/3] dfu: Introduction of the "dfu_checksum_method" env variable for checksum method setting

[Lukasz Majewski]

Hi Tormod,

> On Mon, Mar 31, 2014 at 10:44 PM, Lukasz Majewski wrote:
> > The DFU 1.1 standard in its appendinx B specifies the DFU suffix.
> > It has the crc32 for the whole file, vendorID, device ID and other
> > handy fields.
> >
> > Unfortunately, this part of the standard is not supported neither at
> > dfu implementation in u-boot nor dfu-util (v.0.5 - debian).
> >
> > It would be handy for small files (like bootloaders, kernels) where
> > we download all the data at once. For critical files it should be
> > definitely implemented. From my glimpse observation the dfu-util
> > would require some extension to support the DFU suffix (Tormod,
> > please correct me if I'm wrong).
> 
> You are wrong :) Please don't use what's available in Debian (stable?)
> as a reference.

I'm regarding this as a reference since 80% of developers will download
the dfu-util with apt-get on debian.

> I don't know what their maintainer is up to. dfu-util
> supports the DFU suffix according to the DFU standard. That means it
> checks the CRC after reading the file, and also checks that
> vendor/product values match, then sends the firmware to the device
> after stripping off the suffix.

So this means that:
1. The file before reading by dfu-util has to be equipped with suffix.
2. The dfu-util reads it and then if matching sends data (with sufix
stripped) to target. This means that we are "protected" from downloading
wrong firmware to device, however
3. The target doesn't have any means to check if the downloaded data is
consistent - the information about CRC is stripped at dfu-util.

> 
> Are you wanting to do some CRC checking at the device side? That would
> be outside the DFU standard. 

I hoped that the suffix is appended by dfu-util and then sent with the
binary to target. As a result we would be able to perform some integrity
tests.

> But you can always put whatever you want
> in the "firmware", including proprietary headers or suffices.

I think that this would be finally required for updating small (crucial)
files - like bootloaders, kernels.

> We
> already support some of those, please see the dfu-util (and
> dfu-suffx/dfu-prefix) code at dfu-util.gnumonks.org.

Ok, I see. This would probably require extension of ./src/prefix.c file.
In this way u-boot community would impose some kind of standard
prefix/suffix only for u-boot. It's a pity, that integrity checking is
not standardized in the DFU.

> 
> Regards,
> Tormod


-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group