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

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hello Simon,

On Tue, 3 Feb 2015 18:01:49 -0700, Simon Glass <sjg@chromium.org> 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.

I can tell it does. :)

> 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.

Agreed for me: no board should have DM enabled 'behind its back'.

If RSA depends on DM, then the make menuconfig user should be unable to
select RSA unless and until (s)he has selected DM (and the RSA help
should make it clear that the board must support DM, and that just
enabling CONFIG_DM probably won't be enough).

> Perhaps soon we can enable CONFIG_DM globally but we are not there yet.
>
> Regards,
> Simon

Amicalement,
-- 
Albert.