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

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Date:   Tue, 10 Sep 2019 10:48:29 -0500
From:   Adam Ford <aford173@...il.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Pali Rohár <pali.rohar@...il.com>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Tero Kristo <t-kristo@...com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Adam Ford <adam.ford@...icpd.com>,
        Benoît Cousson <bcousson@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Paul Walmsley <paul@...an.com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC] ARM: omap3: Enable HWMODS for HW Random Number Generator

On Mon, Sep 9, 2019 at 11:35 AM Tony Lindgren <tony@...mide.com> wrote:
>
> * Pali Rohár <pali.rohar@...il.com> [190909 13:41]:
> > On Monday 09 September 2019 08:37:09 Adam Ford wrote:
> > > I applied this on 5.3 and it is working.  I assume the same is true in for-next.
>
> Hmm I noticed I stopped getting RNG data after several rmmod modprobe
> cycles, or several hd /dev/random reads. Anybody else seeing that?
>
> > > Do you want to submit a formal patch?  I  can mark it as 'tested-by'
> > > This really helps speed up the startup sequence on boards with sshd
> > > because it delays for nearly 80 seconds waiting for entropy without
> > > the hwrng.
> >
> > Hi! When applying a patch, could you please disable this rng for n900?
> >
> > In omap3-n900.dts for rng should be status = "disabled" (as Tony already
> > wrote), similarly like for aes.
>
> Yeah I'll post a proper patch after -rc1.

FYI,

By putting your node into omap34xx.dtsi and omap36xx.dtsi along with
the following, I can get the RNG to work on an OMAP3530 and a DM3730.


diff --git a/arch/arm/boot/dts/omap34xx-omap36xx-clocks.dtsi
b/arch/arm/boot/dts/omap34xx-omap36xx-clocks.dtsi
index 5e9d1afcd422..73f351e6d132 100644
--- a/arch/arm/boot/dts/omap34xx-omap36xx-clocks.dtsi
+++ b/arch/arm/boot/dts/omap34xx-omap36xx-clocks.dtsi
@@ -259,7 +259,7 @@
                         <&i2c1_ick>, <&uart2_ick>, <&uart1_ick>, <&gpt11_ick>,
                         <&gpt10_ick>, <&mcbsp5_ick>, <&mcbsp1_ick>,
                         <&omapctrl_ick>, <&aes2_ick>, <&sha12_ick>, <&icr_ick>,
-                        <&des2_ick>, <&mspro_ick>, <&mailboxes_ick>,
+                        <&des2_ick>, <&mspro_ick>, <&mailboxes_ick>,
<&rng_ick>,
                         <&mspro_fck>;
        };
 };

I tried doing the same for am3517, but it doesn't appear to work.  In
fact, the board hangs at boot with no splat, so I assume that some
clock isn't running and causing a hang.  Figure 4-50 in the AM3517 TRM
shows the security_l4_iclk2, so I wonder if the HW mods for AES, SHA,
etc are doing something to enable this clock.  Those HWmods are
disabled on AM3517.  I tried turning on the hwmods for them before
without success, but I'll try it again.

adam
>
> Regards,
>
> Tony