[ Upstream commit b407460ee99033503993ac7437d593451fcdfe44 ]
It is considered good practice to call cpu_relax() in busy loops, see
Documentation/process/volatile-considered-harmful.rst. This can not
only lower CPU power consumption or yield to a hyperthreaded twin
processor, but also allows an architecture to mitigate hardware issues
(e.g. ARM Erratum 754327 for Cortex-A9 prior to r2p0) in the
architecture-specific cpu_relax() implementation.
In addition, cpu_relax() is also a compiler barrier. It is not
immediately obvious that the @op argument "function" will result in an
actual function call (e.g. in case of inlining).
Where a function call is a C sequence point, this is lost on inlining.
Therefore, with agressive enough optimization it might be possible for
the compiler to hoist the:
(val) = op(args);
"load" out of the loop because it doesn't see the value changing. The
addition of cpu_relax() would inhibit this.
As the iopoll helpers lack calls to cpu_relax(), people are sometimes
reluctant to use them, and may fall back to open-coded polling loops
(including cpu_relax() calls) instead.
Fix this by adding calls to cpu_relax() to the iopoll helpers:
- For the non-atomic case, it is sufficient to call cpu_relax() in
case of a zero sleep-between-reads value, as a call to
usleep_range() is a safe barrier otherwise. However, it doesn't
hurt to add the call regardless, for simplicity, and for similarity
with the atomic case below.
- For the atomic case, cpu_relax() must be called regardless of the
sleep-between-reads value, as there is no guarantee all
architecture-specific implementations of udelay() handle this.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/45c87bec3397fdd704376807f0eec5cc71be440f.1685692810.git.geert+renesas@glider.be
Signed-off-by: Sasha Levin <sashal@kernel.org>
redefined readx_poll_timeout macro by read_poll_timeout to
simplify the code.
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
this macro is an extension of readx_poll_timeout macro. the accessor
function op just supports only one parameter in the readx_poll_timeout
macro, but this macro can supports multiple variable parameters for
it. so functions like phy_read(struct phy_device *phydev, u32 regnum)
and phy_read_mmd(struct phy_device *phydev, int devad, u32 regnum) can
also use this poll timeout core. and also expand it can sleep some time
before read operation.
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
The conversion here is really trivial: just a bunch of title
markups and very few puntual changes is enough to make it to
be parsed by Sphinx and generate a nice html.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Based on 1 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 and
only version 2 as published by the free software foundation this
program is distributed in the hope that it will be useful but
without any warranty without even the implied warranty of
merchantability or fitness for a particular purpose see the gnu
general public license for more details
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 294 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190529141900.825281744@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
When we pass the result of a multiplication as the timeout or the delay,
we can get a warning from gcc-7:
drivers/mmc/host/bcm2835.c:596:149: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]
drivers/mfd/arizona-core.c:247:195: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]
drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c:49:27: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]
The warning is a bit questionable inside of a macro, but this is
intentional on the side of the gcc developers. It is also an indication
of another problem: we evaluate the timeout and sleep arguments multiple
times, which can have undesired side-effects when those are complex
expressions.
This changes the two iopoll variants to use local variables for storing
copies of the timeouts. This adds some more type safety, and avoids
both the double-evaluation and the gcc warning.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81484
Link: http://lkml.kernel.org/r/20170726133756.2161367-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/20171102114048.1526955-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
