Re: [RFC] ARM: omap3: Enable HWMODS for HW Random Number Generator

From: Pali RohÃr
Date: Tue Sep 10 2019 - 10:44:58 EST

On Tuesday 10 September 2019 15:37:32 Sebastian Reichel wrote:
> Hi,
> On Tue, Sep 10, 2019 at 08:56:49AM -0500, Adam Ford wrote:
> > On Thu, Sep 5, 2019 at 6:04 PM Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> > > Oh and this needs to default to status = "disabled" for
> > > HS devices like n900 as it needs to use the omap3-rom-rng.
> >
> > I don't know enough about the HS version of the OMAP3, but what's the
> > main difference between omap3-rom-rng and this one?
> The OMAP HS chips have the bus firewall configured to block direct
> access to some cryptography related devices. The kernel will crash
> with a bus error, if you try to read/write the registers for
> protected devices.

And if you try to read it more times, SOC would be rebooted for security

> The omap3-rom-rng avoids this by communicating
> with the security middleware component instead of directly accessing
> the RNG hardware.

And that component is loaded by signed bootloader into "secure" area not
accessible by "non-secure" work (like kernel) and communication is done
via arm smc instruction.

Pali RohÃr