https://github.com/torvalds/linux
Revision cbd0e4821373ab10833c38edc3b858e3fa1a2976 authored by Linus Torvalds on 08 May 2020, 15:56:16 UTC, committed by Linus Torvalds on 08 May 2020, 15:56:16 UTC
Pull tty/serial fixes from Greg KH: "Here are three small TTY/Serial/VT fixes for 5.7-rc5: - revert for the bcm63xx driver "fix" that was incorrect - vt unicode console bugfix - xilinx_uartps console driver fix All of these have been in linux next with no reported issues" * tag 'tty-5.7-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: tty: xilinx_uartps: Fix missing id assignment to the console vt: fix unicode console freeing with a common interface Revert "tty: serial: bcm63xx: fix missing clk_put() in bcm63xx_uart"
Tip revision: cbd0e4821373ab10833c38edc3b858e3fa1a2976 authored by Linus Torvalds on 08 May 2020, 15:56:16 UTC
Merge tag 'tty-5.7-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
Merge tag 'tty-5.7-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
Tip revision: cbd0e48
atomic_bitops.txt
=============
Atomic bitops
=============
While our bitmap_{}() functions are non-atomic, we have a number of operations
operating on single bits in a bitmap that are atomic.
API
---
The single bit operations are:
Non-RMW ops:
test_bit()
RMW atomic operations without return value:
{set,clear,change}_bit()
clear_bit_unlock()
RMW atomic operations with return value:
test_and_{set,clear,change}_bit()
test_and_set_bit_lock()
Barriers:
smp_mb__{before,after}_atomic()
All RMW atomic operations have a '__' prefixed variant which is non-atomic.
SEMANTICS
---------
Non-atomic ops:
In particular __clear_bit_unlock() suffers the same issue as atomic_set(),
which is why the generic version maps to clear_bit_unlock(), see atomic_t.txt.
RMW ops:
The test_and_{}_bit() operations return the original value of the bit.
ORDERING
--------
Like with atomic_t, the rule of thumb is:
- non-RMW operations are unordered;
- RMW operations that have no return value are unordered;
- RMW operations that have a return value are fully ordered.
- RMW operations that are conditional are unordered on FAILURE,
otherwise the above rules apply. In the case of test_and_{}_bit() operations,
if the bit in memory is unchanged by the operation then it is deemed to have
failed.
Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics and
clear_bit_unlock() which has RELEASE semantics.
Since a platform only has a single means of achieving atomic operations
the same barriers as for atomic_t are used, see atomic_t.txt.
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