Date:   Mon, 30 Aug 2021 18:28:04 +0200
From:   Fredrik Yhlen <fredrik.yhlen@...ian.se>
To:     Fabio Estevam <festevam@...il.com>
Cc:     Horia Geanta Neag <horia.geanta@....com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        Heiko Schocher <hs@...x.de>
Subject: Re: HRNG in CAAM isn't working properly on IMX6 SoloX

Hi Pablo,

It seems to be working with your suggested change and PR enabled:
```
root@...x:/dev# dd bs=256 count=10 if=/dev/hwrng of=/dev/null
10+0 records in
10+0 records out
2560 bytes (2.6 kB, 2.5 KiB) copied, 14.5987 s, 0.2 kB/s
root@...x:/dev#
```

Thanks!

Best regards,
Fredrik

On Mon, Aug 30, 2021 at 08:49:25AM -0300, Fabio Estevam wrote:
> Hi Fredrik,
> 
> On Mon, Aug 30, 2021 at 8:22 AM Fredrik Yhlen <fredrik.yhlen@...ian.se> wrote:
> >
> > Hi,
> >
> > We're having problems with hwrng on a board with imx6sx (soloX) running Linux
> > 5.10.x. mainline, and I have tracked it down to this commit
> > '358ba762d9f1d4ba99ab31ef12bc28014b22f4c9' as being the culprit.
> >
> > The caam_jr driver spits out lots of messages when attempting to read from /dev/hwrng:
> > ```
> > [29717.629041] hwrng: no data available
> > [29727.859008] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG: Hardware error
> > ```
> >
> > ```
> > caam_jr 2101000.jr0: 2000025b: CCB: desc idx 2: RNG: Hardware error.
> > caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error.
> > caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error.
> > caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error.
> > caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error.
> > caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error.
> > ```
> >
> > This also happens on Boundary's Nitrogen6_soloX board when running the same
> > kernel, and likewise with their latest Yocto release that uses 5.4.100 linux-imx kernel.
> >
> > ```
> > root@...rogen6sx:~# dd if=/dev/hwrng of=/tmp/random bs=256 count=10
> > [  113.940735] caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error
> > dd: /dev/hwrng: Invalid argument
> > root@...rogen6sx:~# rm /tmp/random
> > root@...rogen6sx:~# dd if=/dev/hwrng of=/tmp/random bs=256 count=10
> > [  125.300823] caam_jr 2101000.jr0: 20003c5b: CCB: desc idx 60: RNG: Hardware error
> > dd: /dev/hwrng: Invalid argument
> > root@...rogen6sx:~# du -hs /tmp/random
> > 0       /tmp/random
> > root@...rogen6sx:~# ls -l /tmp/random
> > -rw-r--r--    1 root     root             0 Dec 16 17:27 /tmp/random
> > root@...rogen6sx:~#
> > ```
> >
> > And then no data is available from /dev/hwrng.
> >
> > The problem occurs when adding OP_ALG_PR_ON(prediction resistance) when setting up
> > job descriptor for reading new random data in caamrng.c. There are also
> > some confusing parts about this commit that I'm not too sure about.
> >
> > 1. It's adding a conditional variable named 'pr_support', but I guess this only
> > indicates if the MC(Management Complex) supports prediction resistance,
> > since the following check can be bypassed when 'pr_support' is false.
> >
> >     /*
> >      * If SEC has RNG version >= 4 and RNG state handle has not been
> >      * already instantiated, do RNG instantiation
> >      * In case of SoCs with Management Complex, RNG is managed by MC f/w.
> >      */
> >     if (!(ctrlpriv->mc_en && pr_support) && rng_vid >= 4) {
> >
> >
> > This will eventually lead to the following chain call: caam_probe() -> instantiate_rng() ->
> > build_instantiation_desc(), where OP_ALG_PR_ON will be used through DECO.
> >
> > static void build_instantiation_desc(u32 *desc, int handle, int do_sk)
> > {
> >     u32 *jump_cmd, op_flags;
> >
> >     init_job_desc(desc, 0);
> >
> >     op_flags = OP_TYPE_CLASS1_ALG | OP_ALG_ALGSEL_RNG |
> >             (handle << OP_ALG_AAI_SHIFT) | OP_ALG_AS_INIT |
> >             OP_ALG_PR_ON;
> >     ...
> >     ...
> >     ...
> >
> > Shouldn't it be named 'mc_pr_support' instead, or something similar?
> >
> > 2. PR is unconditionally used in caamrng.c(caam_jr module) when
> > reading new RNG data. Should this be the case?
> >
> > Removing OP_ALG_PR_ON in caam_init_desc() from drivers/crypto/caam/caamrng.c
> > seems to fix the problem we're experiencing, here's an example:
> > ```
> > diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.c
> > index 77d048dfe5d0..f085a80b1b3c 100644
> > --- a/drivers/crypto/caam/caamrng.c
> > +++ b/drivers/crypto/caam/caamrng.c
> > @@ -67,8 +67,7 @@ static u32 *caam_init_desc(u32 *desc, dma_addr_t dst_dma)
> >  {
> >         init_job_desc(desc, 0); /* + 1 cmd_sz */
> >         /* Generate random bytes: + 1 cmd_sz */
> > -       append_operation(desc, OP_ALG_ALGSEL_RNG | OP_TYPE_CLASS1_ALG |
> > -                        OP_ALG_PR_ON);
> > +       append_operation(desc, OP_ALG_ALGSEL_RNG | OP_TYPE_CLASS1_ALG);
> >         /* Store bytes: + 1 cmd_sz + caam_ptr_sz  */
> >         append_fifo_store(desc, dst_dma,
> >                           CAAM_RNG_MAX_FIFO_STORE_SIZE, FIFOST_TYPE_RNGSTORE);
> > ```
> 
> We also observe this issue.
> 
> Heiko on Cc tried increasing the RTSDCTL_ENT_DLY_MIN value
> and this seems to help:
> 
> diff --git a/drivers/crypto/caam/regs.h b/drivers/crypto/caam/regs.h
> index af61f3a2c0d4..53c9fa04a24c 100644
> --- a/drivers/crypto/caam/regs.h
> +++ b/drivers/crypto/caam/regs.h
> @@ -513,7 +513,7 @@ struct rng4tst {
>   };
>  #define RTSDCTL_ENT_DLY_SHIFT 16
>  #define RTSDCTL_ENT_DLY_MASK (0xffff << RTSDCTL_ENT_DLY_SHIFT)
> -#define RTSDCTL_ENT_DLY_MIN 3200
> +#define RTSDCTL_ENT_DLY_MIN 4800
>  #define RTSDCTL_ENT_DLY_MAX 12800
>   u32 rtsdctl; /* seed control register */
>   union {
> 
> Does this help in your case?
> 
> Thanks,
> 
> Fabio Estevam

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