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

From: Adam Ford
Date: Tue Sep 10 2019 - 11:48:43 EST

On Mon, Sep 9, 2019 at 11:35 AM Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> * Pali RohÃr <pali.rohar@xxxxxxxxx> [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.


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
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>,

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.

> Regards,
> Tony