hwrng: st - add MODULE_DESCRIPTION

Add a MODULE_DESCRIPTION to fix the W=1 warning

WARNING: modpost: missing MODULE_DESCRIPTION() in
drivers/char/hw_random/st-rng.o

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: st - keep clock enabled while hwrng is registered

The st-rng driver uses devres to register itself with the hwrng core,
the driver will be unregistered from hwrng when its device goes out of
scope. This happens after the driver's remove function is called.

However, st-rng's clock is disabled in the remove function. There's a
short timeframe where st-rng is still registered with the hwrng core
although its clock is disabled. I suppose the clock must be active to
access the hardware and serve requests from the hwrng core.

Switch to devm_clk_get_enabled and let devres disable the clock and
unregister the hwrng. This avoids the race condition.

Fixes: 3e75241be808 ("hwrng: drivers - Use device-managed registration API")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: st - Fix W=1 unused variable warning

This patch fixes an unused variable warning when this driver is
built-in with CONFIG_OF=n.

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

hwrng: st - use devm_platform_ioremap_resource() to simplify code

Use devm_platform_ioremap_resource() to simplify the code a bit.
This is detected by coccinelle.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: drivers - Use device-managed registration API

Use devm_hwrng_register to simplify the implementation.
Manual unregistration and some remove functions can be
removed now.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Acked-by: Łukasz Stelmach <l.stelmach@samsung.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500

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>

hwrng: st - Fix missing clk_disable_unprepare() on error in st_rng_probe()

Fix the missing clk_disable_unprepare() before return
from st_rng_probe() in the error handling case.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: Remove check for max less than 4 bytes

HW RNG core never asks for data less than 4 bytes. The check whether max
is less than 4 bytes is unnecessary. Remove the check.

Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: st - Improve FIFO size/depth description

The original representation of FIFO size in the driver coupled with the
ambiguity in the documentation meant that it was easy to confuse readers.
This lead to a false positive BUG-find and subsequently time wastage
debugging this phantom issue.

Hopefully this patch can prevent future readers from falling into the
same trap.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: st - Use real-world device timings for timeout

Samples are documented to be available every 0.667us, so in theory
the 8 sample deep FIFO should take 5.336us to fill. However, during
thorough testing, it became apparent that filling the FIFO actually
takes closer to 12us.

Also take into consideration that udelay() can behave oddly i.e. not
delay for as long as requested.

Suggested-by: Russell King <rmk+kernel@arm.linux.org.uk>:

"IIRC, Linus recommends a x2 factor on delays, especially
timeouts generated by these functions.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: st - Add support for ST's HW Random Number Generator

Signed-off-by: Pankaj Dev <pankaj.dev@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Kieran Bingham <kieranbingham@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>