RE: [PATCH 1/3] hw/misc: Introduce AMD/Xilix Versal TRNG device

[Ho, Tong]

Hi Peter,

Your recommendation is noted.  Thanks for your valuable input.  I will present 
V2 with better alignment.

Regards,
Tong Ho

-----Original Message-----
From: Peter Maydell <peter.maydell@linaro.org> 
Sent: Friday, September 8, 2023 11:35 AM
To: Ho, Tong <tong.ho@amd.com>
Cc: Richard Henderson <richard.henderson@linaro.org>; qemu-arm@nongnu.org; 
qemu-devel@nongnu.org; alistair@alistair23.me; edgar.iglesias@gmail.com
Subject: Re: [PATCH 1/3] hw/misc: Introduce AMD/Xilix Versal TRNG device

On Fri, 8 Sept 2023 at 18:56, Ho, Tong <tong.ho@amd.com> wrote:
>
> Hi Peter,
>
> The Versal TRNG device is required to support both TRNG mode and PRNG 
> mode, and target/guest software selects and changes the mode at will during 
> runtime.
>
> I do agree that, in the TRNG mode, the model using qemu_guest_getrandom() 
> will work without any issues.
>
> When software selects the PRNG mode, the Versal TRNG device is 
> expected to output a reproducible and deterministic sequence of values for a 
> given seed.  This is part of the hardware spec.
>
> I fail to see how qemu_guest_getrandom() can be used to model such 
> requirement correctly.

If the hardware documents a specific RNG that it must use, then yes, we should 
model that, and the comments need to make it clear that we're modelling a very 
specific thing, not merely "here is an arbitrary PRNG".

-- PMM