Re: Issues with HW RNG / SSS on Exynos 5422

[Krzysztof Kozlowski <k.kozlowski@samsung.com>]

On 17.08.2015 15:10, Heiner Kallweit wrote:
> Am 17.08.2015 um 02:19 schrieb Krzysztof Kozlowski:
>> 2015-08-16 20:18 GMT+09:00 Heiner Kallweit <hkallweit1@gmail.com>:
>>> Am 15.08.2015 um 13:19 schrieb Heiner Kallweit:
>>>> I'm having issues making the hardware RNG work on a Samsung Exynos 5422 (Odroid XU4) with kernel 4.2rc6.
>>>> No random number generation is started if I write the appropriate value (0x18) to the hash control register.
>>>>
>>>> What I did so far:
>>>> Splitted the sss DT node in exynos5420.dtsi into one for the s5p-sss driver and one for the exynos-rng driver.
>>>> (s5p-sss doesn't seem to need the hash registers from offset 0x400)
>>>>
>>>> sss: sss@10830000 {
>>>>       icompatible = "samsung,exynos4210-secss";
>>>>       reg = <0x10830000 0x400>;
>>>>       interrupts = <0 112 0>;
>>>>       clocks = <&clock CLK_SSS>;
>>>>       clock-names = "secss";
>>>> };
>>>>
>>>> rng: rng@10830400 {
>>>>       compatible = "samsung,exynosrng-secss";
>>>>       reg = <0x10830400 0x300>;
>>>>       clocks = <&clock CLK_SSS>;
>>>>       clock-names = "secss";
>>>> };
>>>>
>>>> The DT binding is just for testing and after adding some DT glue logic (of_device_id table) to the exynos-rng driver
>>>> it binds to the rng platform device.
>>>> The clock also seems to be ok with a rate of 266 MHz.
>>>> As is the driver hangs in a loop because the PRNG_DONE in the status register bit never gets set.
>>>>
>>>> I traced it back to the hash control register not accepting value 0x8 (or 0x18 incl. the start bit) for the PRNG.
>>>> Writing a value and reading it back works for values from 0 to 5 only.
>>>> As I have no SSS datasheet my only other reference is drivers/crypto/ace_sha.h in the uboot source code
>>>> which also uses the HW RNG.
>>>>
>>>> Any hint would be appreciated.
>>>>
>>> After some more testing it seems like SSS in general has problems on Exynos 5422.
>>> Also the AES implementation in s5p-sss doesn't work. dmesg output:
>>>
>>> [    7.116739] alg: skcipher: encryption failed on chunk test 1 for ecb-aes-s5p: ret=22
>>> [    7.123673] s5p-sss driver registered
>>
>> Have you tried or looked at vendor code for Samsung mobile devices?
>> The code can be downloaded from opensource.samsung.com. I think the
>> model with Exynos5422 is SM-G900H.
>>
>> I don't have any other hints...
>>
>> Best regards,
>> Krzysztof
>> .
>>
> Thanks for your feedback.
> 
> I now took a look at the kernel code Odroid provides, especially the ACE crypto driver.
> It's a 3.10.82 kernel with a lot of Samsung code which is not (yet) upstreamed.
> 
> There seem to be different revisions of SSS (ACE driver mentions v.4, v.5, v.6, and Slim SSS).
> The vendor kernel uses Slim SSS and the HW AES encryption works.
> The code there looks like Exynos 5422 should support also v.5, but it's disabled.
> 
> I didn't test all SSS registers but for the ones I tested I can change the value.
> Having said that access to SSS registers is not forbidden.
> 
> Then I changed the memory mapped region to 0x10900000, offset 0x800. According to the
> vendor kernel code there should be the registers for hash functions under Slim SSS.
> 
> Not much luck either .. Maybe because Slim SSS uses another clock.
> The Slim SSS clock is defined in include/dt-bindings/clock/exynos5420.h already.
> I added a clock definition based on the one in the vendor kernel and changed the DT node to use it.
> 
>         GATE(CLK_SSS, "sss", "aclk266_g2d", GATE_IP_G2D, 2, 0, 0),
> +       GATE(CLK_SLIM_SSS, "slimsss", "aclk266_g2d", GATE_IP_G2D, 12, 0, 0),
> 
> But this didn't do the trick yet.

Try booting with "clk_ignore_unused" in command line to reduce the
chance that wrong clock-hierarchy causes some important clocks to be gated.

The clock hierarchy for SSS in mainline is not fully implemented. Beside
multiple SSS clocks in GATE_IP_G2D and other places, there are also SSS
bus clocks in GATE_BUS_G2D. By default (after reset) they are not gated
but who knows what bootloader does with them?

Best regards,
Krzysztof