[U-Boot] [PATCH 4/4] ARM: tegra210: gpu: configure WPR region

[Thierry Reding <treding@nvidia.com>]

On Mon, Nov 09, 2015 at 08:19:48AM -0700, Stephen Warren wrote:
> On 11/09/2015 07:36 AM, Thierry Reding wrote:
> >On Wed, Oct 28, 2015 at 11:59:04AM -0600, Stephen Warren wrote:
> >>On 10/18/2015 10:57 PM, Alexandre Courbot wrote:
> >>>T210's GPU secure firmware loading requires a write-protected region
> >>>to be set up.
> >>>
> >>>This patch reserves the upper 256KB of RAM as the WPR region and locks
> >>>it so the kernel can initiate secure firmware loading.
> >>
> >>On T210, it's the responsibility of nvtboot (which runs before U-Boot) to
> >>set up any and all carve-outs. This code should not be necessary, and indeed
> >>I expect the registers it touches can't actually be programmed from U-Boot,
> >>which runs in non-secure mode after WPR is already locked.
> >
> >Can we document this assumption somewhere? It's entirely possible that
> >someone might want to run U-Boot without nvtboot
> 
> That's not currently a supported use-case.

Isn't the whole point of open-source for people to be able to do all the
things that aren't supported?

> >, in which case nvtboot
> >would still need to be responsible for setting this up.
> 
> I assume s/nvtboot/whatever other bootloader is in use/?

Right, I was going to write U-Boot here, but that's obviously only true
if U-Boot is still running in secure mode. Otherwise, yes, it'd be what-
ever is the other bootloader being used.

> >Or if it isn't
> >we could still point at some location where the interactions between a
> >first stage bootloader and U-Boot are documented.
> >
> >Do we have a document of this kind already?
> 
> The L4T U-Boot source code:-)

There's a bunch of things that even the L4T U-Boot doesn't document. The
fact that it doesn't initialize the SMMU or WPR doesn't indicate that it
is something that a first stage bootloader needs to do.

Thierry
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