linux-kernel - Re: [PATCH] arm64: dts: ti: k3-am62p-j722s: add rng node

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Message-Id: <D8UECOJ2NMCU.3ALYIKSODJ479@kernel.org>
Date: Mon, 31 Mar 2025 12:58:25 +0200
From: "Michael Walle" <mwalle@...nel.org>
To: "Kumar, Udit" <u-kumar1@...com>, "Nishanth Menon" <nm@...com>, "Vignesh
 Raghavendra" <vigneshr@...com>, "Tero Kristo" <kristo@...nel.org>, "Rob
 Herring" <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>
Cc: <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: ti: k3-am62p-j722s: add rng node

Hi Udit,

> > Add the node for the random number generator inside the crypto module.
> >
> > Signed-off-by: Michael Walle <mwalle@...nel.org>
> > ---
> > This was tested on a J722S/AM67A. Also, according to the TRM this is the
>
> Could you re-confirm please , after adding this node.  you selected trng 
> offered by Linux

# cat /sys/devices/virtual/misc/hw_random/rng_current
40910000.rng
# cat /sys/devices/virtual/misc/hw_random/rng_available
40910000.rng
# dd if=/dev/hwrng bs=16 count=1 | hexdump -C
1+0 records in
1+0 records out
00000000  92 f5 44 09 fd 86 6b a2  39 d6 ad f3 e6 ec 03 4a  |..D...k.9......J|
00000010
# dd if=/dev/hwrng bs=16 count=1 | hexdump -C
1+0 records in
1+0 records out
00000000  a3 73 da d2 5b 94 83 2a  75 11 ca b3 99 d3 87 88  |.s..[..*u.......|
00000010

> > MCU instance of the SA3UL. But it's defined in -main.dtsi. Is this
> > correct?
>
> Yes this is correct,
>
> please refer
>
> https://www.ti.com/lit/zip/sprujb3  SPRUJB3A.pdf
>
> table 2.1 Main Memory map, this node falls under main domain

Ok. Not sure, how I came to the conclusion that this is an MCU
instance.

> > ---
> >   arch/arm64/boot/dts/ti/k3-am62p-j722s-common-main.dtsi | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/ti/k3-am62p-j722s-common-main.dtsi b/arch/arm64/boot/dts/ti/k3-am62p-j722s-common-main.dtsi
> > index 6e3beb5c2e01..e868e006318e 100644
> > --- a/arch/arm64/boot/dts/ti/k3-am62p-j722s-common-main.dtsi
> > +++ b/arch/arm64/boot/dts/ti/k3-am62p-j722s-common-main.dtsi
> > @@ -227,9 +227,17 @@ crypto: crypto@...00000 {
> >   		reg = <0x00 0x40900000 0x00 0x1200>;
> >   		#address-cells = <2>;
> >   		#size-cells = <2>;
> > +		ranges = <0x00 0x40900000 0x00 0x40900000 0x00 0x30000>;
> > +
> >   		dmas = <&main_pktdma 0xf501 0>, <&main_pktdma 0x7506 0>,
> >   		       <&main_pktdma 0x7507 0>;
> >   		dma-names = "tx", "rx1", "rx2";
> > +
> > +		rng: rng@...10000 {
> > +			compatible = "inside-secure,safexcel-eip76";
> > +			reg = <0x00 0x40910000 0x0 0x7d>;
> > +			interrupts = <GIC_SPI 129 IRQ_TYPE_LEVEL_HIGH>;
>
> For completeness , this is ok to add this node but should be kept disabled

Shouldn't it be "reserved" then, see [1].

> similar to
>
> https://github.com/torvalds/linux/blob/master/arch/arm64/boot/dts/ti/k3-j7200-mcu-wakeup.dtsi#L662 

j784s4, j721e and j721s2 have them enabled. What is the rule here?

You also disable the hwrng in optee in your evm according to [2]:
CFG_WITH_SOFTWARE_PRNG=y

-michael

[1] https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html?highlight=reservered#status
[2] https://docs.u-boot.org/en/latest/board/ti/j722s_evm.html

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