Re: [PATCH] omap-rng: Change RNG_CONFIG_REG to RNG_CONTROL_REG when checking and disabling TRNG

[Herbert Xu <herbert@gondor.apana.org.au>]

On Mon, Mar 16, 2015 at 10:19:11AM +1100, Andre Wolokita wrote:
> In omap4_rng_init(), a check of bit 10 of the RNG_CONFIG_REG is done to determine
> whether the RNG is running. This is suspicious firstly due to the use of
> RNG_CONTROL_ENABLE_TRNG_MASK and secondly because the same mask is written to
> RNG_CONTROL_REG after configuration of the FROs. Similar suspicious logic is
> repeated in omap4_rng_cleanup() when RNG_CONTROL_REG masked with
> RNG_CONTROL_ENABLE_TRNG_MASK is read, the same mask bit is cleared, and then
> written to RNG_CONFIG_REG. Unless the TRNG is enabled with one bit in RNG_CONTROL
> and disabled with another in RNG_CONFIG and these bits are mirrored in some way,
> I believe that the TRNG is not really shutting off.
> 
> Apart from the strange logic, I have reason to suspect that the OMAP4 related
> code in this driver is driving an Inside Secure IP hardware RNG and strongly
> suspect that bit 10 of RNG_CONFIG_REG is one of the bits configuring the
> sampling rate of the FROs. This option is by default set to 0 and is not being
> set anywhere in omap-rng.c. Reading this bit during omap4_rng_init() will
> always return 0. It will remain 0 because ~(value of TRNG_MASK in control) will
> always be 0, because the TRNG is never shut off. This is of course presuming
> that the OMAP4 features the Inside Secure IP.
> 
> I'm interested in knowing what the guys at TI think about this, as only they
> can confirm or deny the detailed structure of these registers.
> 
> Signed-off-by: Andre Wolokita <Andre.Wolokita@analog.com>

Both patches applied.  Thanks!
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
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