This patch is based on a vendor patch in U-Boot, taken from
https://portland.source.codeaurora.org/patches/external/imxsupport/uboot-imx/imx_v2016.03_4.1.15_2.0.0_ga/HAB-238-Run-RNG-self-test-for-impacted-i.MX-chips.zip

|    HAB-238 Run RNG self test for impacted i.MX chips
|
|    Patch is only applicable to imx_v2016.03_4.1.15_2.0.0_ga branch of u-boot.
|    Please adapt the patch for your respective release version.
|
|    Background:
|    Few i.MX chips which have HAB 4.2.3 or beyond, have oberserved following
|    warning message generated by HAB due to incorrect implementation of drng
|    self test in boot ROM.
|
|        Event       |0xdb|0x0024|0x42| SRCE Field: 69 30 e1 1d
|                    |    |      |    |             STS = HAB_WARNING (0x69)
|                    |    |      |    |             RSN = HAB_ENG_FAIL (0x30)
|                    |    |      |    |             CTX = HAB_CTX_ENTRY (0xE1)
|                    |    |      |    |             ENG = HAB_ENG_CAAM (0x1D)
|                    |    |      |    | Evt Data (hex):
|                    |    |      |    |  00 08 00 02 40 00 36 06 55 55 00 03 00 00 00 00
|                    |    |      |    |  00 00 00 00 00 00 00 00 00 00 00 01
|
|    It is recommended to run this rng self test before any RNG related crypto
|    implementations are done.
|
[...]
|
|    Signed-off-by: Utkarsh Gupta <utkarsh.gupta@nxp.com>

Currently known impacted chips, as determined by NXP, include:
* i.MX6DQ+ silicon revision 1.1
* i.MX6DQ silicon revision 1.6
* i.MX6DLS silicon revision 1.4
* i.MX6SX silicon revision 1.4
* i.MX6UL silicon revision 1.2
* i.MX67SD silicon revision 1.3

Port the RNG software self-test from this patch to barebox. It can be
enabled by selecting CRYPTO_DEV_FSL_CAAM_RNG_SELF_TEST in Kconfig.

The original patch included a command line utility to run the self-test,
but we choose a different approach here, and run the software self-test
automatically when the respective HAB events indicating a RNG ROM
self-test failure are found when running habv4_get_status(). Note that
habv4_get_status() must be called by the board code before the CAAM
device driver is probed for this mechanism to work.

Until now there are at least two such known events. The first event was
observed on an i.MX6Solo, silicon revision 1.4; the second event is
mentioned in the original patch description given above. When an event
occured, habv4_get_status() tests if it is one of those known events,
and if so, indicates to the CAAM driver to run the software self-test.
In this case, printing the respective HAB warning is suppressed to
prevent confusion; the software self-test itself will error out in case
of recurring RNG self-test failure.

Signed-off-by: Roland Hieber <r.hieber@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>