Most hw_random devices return entropy which is assumed to be of full
quality, but driver authors don't bother setting the quality knob. Some
hw_random devices return less than full quality entropy, and then driver
authors set the quality knob. Therefore, the entropy crediting should be
opt-out rather than opt-in per-driver, to reflect the actual reality on
the ground.

For example, the two Raspberry Pi RNG drivers produce full entropy
randomness, and both EDK2 and U-Boot's drivers for these treat them as
such. The result is that EFI then uses these numbers and passes the to
Linux, and Linux credits them as boot, thereby initializing the RNG.
Yet, in Linux, the quality knob was never set to anything, and so on the
chance that Linux is booted without EFI, nothing is ever credited.
That's annoying.

The same pattern appears to repeat itself throughout various drivers. In
fact, very very few drivers have bothered setting quality=1024.

Looking at the git history of existing drivers and corresponding mailing
list discussion, this conclusion tracks. There's been a decent amount of
discussion about drivers that set quality < 1024 -- somebody read and
interepreted a datasheet, or made some back of the envelope calculation
somehow. But there's been very little, if any, discussion about most
drivers where the quality is just set to 1024 or unset (or set to 1000
when the authors misunderstood the API and assumed it was base-10 rather
than base-2); in both cases the intent was fairly clear of, "this is a
hardware random device; it's fine."

So let's invert this logic. A hw_random struct's quality knob now
controls the maximum quality a driver can produce, or 0 to specify 1024.
Then, the module-wide switch called "default_quality" is changed to
represent the maximum quality of any driver. By default it's 1024, and
the quality of any particular driver is then given by:

    min(default_quality, rng->quality ?: 1024);

This way, the user can still turn this off for weird reasons (and we can
replace whatever driver-specific disabling hacks existed in the past),
yet we get proper crediting for relevant RNGs.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Use devm_hwrng_register to get rid of manual unregistration.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Ensure cooldown period tolerance of 1% is actually accounted for.

Fixes: ca3bff70ab32 ("hwrng: timeriomem - Improve performance...")
Signed-off-by: Jan Henrik Weinstock <jan.weinstock@rwth-aachen.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

The timeriomem_rng driver only accesses the first 4 bytes of the given
memory area and currently, it also forces that memory resource to be
exactly 4 bytes in size.

This, however, is problematic when used with device-trees that are
generated from things like FPGA toolchains, where the minimum size
of an exposed memory block may be something like 4k.

Hence, let's only check for what's needed for the driver to operate
properly; namely that we have enough memory available to read the
random data from.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Based on 2 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license version 2 as
  published by the free software foundation

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license version 2 as
  published by the free software foundation #

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 4122 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

In read routiene max is always >= 4. The check whether 'max < 4' is not
necessary. Remove it.

Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Acked-By: Rick Altherr <raltherr@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

When a hw_random device's quality is non-zero, it will automatically be
used to fill the kernel's entropy pool.  Since timeriomem_rng is used by
many different devices, the quality needs to be provided by platform
data or device tree.

Signed-off-by: Rick Altherr <raltherr@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Some hardware RNGs provide a single register for obtaining random data.
Instead of signaling when new data is available, the reader must wait a
fixed amount of time between reads for new data to be generated.
timeriomem_rng implements this scheme with the period specified in
platform data or device tree.  While the period is specified in
microseconds, the implementation used a standard timer which has a
minimum delay of 1 jiffie and caused a significant bottleneck for
devices that can update at 1us.  By switching to an hrtimer, 1us periods
now only delay at most 2us per read.

Signed-off-by: Rick Altherr <raltherr@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

No functional changes.

Signed-off-by: Rick Altherr <raltherr@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Preserves the existing behavior of only returning 32-bits per call.

Signed-off-by: Rick Altherr <raltherr@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>