[U-Boot] [PATCH v3] dfu: Introduction of the "dfu_hash_algo" env variable for checksum method setting

[Wolfgang Denk]

Dear Lukasz,

In message <20140515090904.32f1d13d at amdc2363> you wrote:
> 
> > > What I complained about is the change in behaviour.  I asked to make
> > > the existing behaviour the default, so unaware users will not be
> > > affected. Only if you intentionally want some other behaviour you
> > > can then enable this by setting the env variable.
> > 
> > Well, looking at mainline usage of DFU, Lukasz is speaking for about
> > half of the users / implementors.  Since Denx is working with the
> > other half, can you shed some light on actual use vs theoretical
> > possibilities?
> 
> I don't want to urge anybody on making any conclusion here :-), but I
> would be very grateful if we could come up with an agreement.
> 
> As I've stated previously, my opinion is similar to the one presented
> by Tom in this message.
> 
> For me it would be best to not calculate any checksum on default and
> only enable it when needed.

I asked Heiko to run some actual tests on the boards where he has to
maintain DFU for.  For a 288 MiB image he did not measure any
difference - with your patch applied, both with and without CRC
enabled, we would get the same (slow) 1:54 minutes download time.

This reinforces my speculation that you are actually addressing the
wrong problem.  Instead of adding new code and environment variables
and making the system even more complex, we should just leave
everything as is, and you should try to find out why the CRC
calculation is so low for you.  Checking if caches are enabled is
probably among the things that should be done first.


Regarding the checksumming topic in general:  the fact that the DFU
standard defines a method to verify the checksum of the image (dwCRC
field in the DFU File Suffix), but does not transmit this vital data
to the target so the actual file download and storage procedure on the
target is completely unprotected is IMO a serious design flaw of the
DFU protocl.  Do you think it would be possible to have this augmented
/ fixed?



Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"Free markets select for winning solutions."        - Eric S. Raymond