[U-Boot] [PATCH] RSA depends on DM

[Robert Moskowitz <rgm@htt-consult.com>]

Of course there is the meta question of why RSA sig is still being used 
rather than ECDSA.

As a crypto plumber, I occationally wonder why we perpetuate need of 
large, slow RSA keys over ECC.  Perhaps the patent concerns even with 
RFC 6090.

I will shut up and let you to your important work of getting all this 
wonderful support working in uboot.

On 02/03/2015 08:01 PM, Simon Glass wrote:
> Hi Chris,
>
> On 3 February 2015 at 17:57, Chris Kuethe <chris.kuethe@gmail.com> wrote:
>> On Tue, Feb 3, 2015 at 4:38 PM, Simon Glass <sjg@chromium.org> wrote:
>>> +Masahiro
>>>
>>> Hi Chris,
>>>
>>> On 3 February 2015 at 00:42, Chris Kuethe <chris.kuethe@gmail.com> wrote:
>>>> Discovered while experimenting with signature checking on vexpress
>>>> which doesn't typically use DM. Rather than complaining about unmet
>>>> dependencies it might be better to enable those them.
>>>>
>>>> ---
>>>>   lib/rsa/Kconfig | 1 +
>>>>   1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
>>>> index 1268a1b..4db5da4 100644
>>>> --- a/lib/rsa/Kconfig
>>>> +++ b/lib/rsa/Kconfig
>>>> @@ -2,6 +2,7 @@ config RSA
>>>>    bool "Use RSA Library"
>>>>    select RSA_FREESCALE_EXP if FSL_CAAM
>>>>    select RSA_SOFTWARE_EXP if !RSA_FREESCALE_EXP
>>>> + select DM
>>>>    help
>>>>     RSA support. This enables the RSA algorithm used for FIT image
>>>>     verification in U-Boot.
>>> I wonder whether 'depends on DM' might be better? It seems odd to have
>>> the tail wagging the dog.
>>>
>>> Regards,
>>> Simon
>> No, that would not be better because a few lines down,
>> RSA_SOFTWARE_EXP and RSA_FREESCALE_EXP both say "depends on DM" but
>> they don't actually enable it if they need it.
>>
>> As a user, my expectation is that when I turn on some high level
>> feature, that will enable all of its lower level dependencies. Would
>> it be less strange to make FIT_SIGNATURE turn on DM instead of RSA?
> We certainly must avoid the build break.
>
> My concern is that CONFIG_DM may introduce a run-time break. For
> example if you don't have pre-relocation malloc() available the board
> may not boot. Driver model is a fundamental core feature, and we are
> working to move everything over to it, but I'm not quite comfortable
> with forcing it on when someone changes a feature. It feel it would be
> better to not offer it.
>
> I'm interested to hear other viewpoints though.
>
> Perhaps soon we can enable CONFIG_DM globally but we are not there yet.
>
> Regards,
> Simon
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