Re: [PATCH] crypto: loongson - Select CRYPTO_RNG

[Qunqin Zhao]

在 2026/5/25 上午11:20, Eric Biggers 写道:
> On Mon, May 25, 2026 at 10:45:14AM +0800, Qunqin Zhao wrote:
> > > > To be honest, I previously assumed that the `hw_random` was designed
> > > > strictly and exclusively for the TRNG mode.
> > > >
> > > > Is it architecturally acceptable or common practice for a PRNG mode to
> > > > utilize `hw_random` as well?
> > > >
> > > > Thanks,
> > > So the Loongson RNG is a PRNG?  Where does it get its entropy from, and
> > > what is its security strength?
> > Loongson's hardware supports both TRNG and PRNG simultaneously.
> >
> > We can locate a reseed function within loongson-rng.c, which clearly
> > indicates that it is a PRNG driver.
> That reseed function gets called with entropy from the Linux RNG.  So,
> it seems it's really just a PRNG seeded from the Linux RNG.  What value
> does that provide over just using the Linux RNG directly?

Alternatively,the reseed function can serve  as a stirring mechanism, 
where the primary entropy comes from the internal hardware TRNG.

Or simply ignore the  entropy from the Linux RNG entirely, trigger a 
reseeding internal.


The driver merely forwards the seed to the firmware; how it is utilized 
and what kind of random numbers are returned are entirely determined by 
the firmware implementation.

> > So the core issue here is whether a PRNG driver can utilize the crypto
> > interface.
> If you're asking about crypto_rng, it can.  But the crypto_rng interface
> is also kind of useless.  If you're asking about hwrng, it does look
> like it's designed for TRNGs.  Would it be possible for this driver to
> use the TRNG mode?

I mean crypto_rng.

We might use the hwrng interface to add support for the TRNG in this driver.

> > If it cannot, does that imply the drivers listed below serve no practical
> > purpose? (7.1-rc1)
> >
> > loongson@loongson:~/upstream/linux/drivers/crypto$ grep crypto_register_rng
> Most of the drivers in drivers/crypto/ are added by the hardware
> manufacturer without any regard for whether they're useful or not.

If we are dropping crypto-rng drivers entirely,

I am fine with removing the Loongson driver along with the others.

However, targeting the Loongson driver alone is unacceptable.


Thanks,

Qunqin.

> - Eric