This patchset introduces an atomic MMIO modify API. The motivation for adding this is to allow cheap, infrastructure-less, thread-safe access to an MMIO region, even in very early scenarios.
The chosen mask/set semantic (proposed by Russell King) is clean and flexible enough and matches the regmap_update_bits() prototype. Consistency is good. This series adds a simple arch-generic implementation in a new lib/atomicio.c file. On top of that it implements an ARM-optimized variant following Will Deacon's suggestions, that take advantage of ARM relaxed read/write functions. Finally, just to show a few usage for this function, last two patches show how this would solve one of the current shared-registers issues. Since this 4th version is no longer ARM-specific but kernel-wide, and perhaps new reviewers might jump in, please read the previous discussion on why this is needed and why we cannot use a regmap API. v1: https://lkml.org/lkml/2013/8/10/75 v2: http://comments.gmane.org/gmane.linux.ports.arm.kernel/261879 v3: http://www.spinics.net/lists/arm-kernel/msg269263.html Thoughts? Changes from v3: * Implemented an arch-generic atomic_io_modify(), as suggested by Baruch and Catalin. * Add an ARM-specific variant, using relaxed R/W as Will suggested. * Replaced spin_locks by raw_spin_locks, to protect the registers even on RT. * Fixed two stupid typos. Changes from v2: * As suggested by Will Deacon, dropped the iowmb() barrier and use relaxed variants instead. See Will's explanation for details: http://www.spinics.net/lists/arm-kernel/msg268775.html * Use spin_{}_irqsave/restore to allow irq-context usage also suggested by Will Deacon. * Re-worked the API semantics as proposed by Russell King. Changes from v1: * Added an io barrier iowmb() as suggested by Will Deacon, to ensure the writel gets completed before the spin_unlock(). Ezequiel Garcia (4): lib: Introduce atomic MMIO modify ARM: Add atomic_io_modify optimized routines clocksource: orion: Use atomic access for shared registers watchdog: orion: Use atomic access for shared registers arch/arm/include/asm/io.h | 4 ++++ arch/arm/kernel/io.c | 29 +++++++++++++++++++++++++++++ drivers/clocksource/time-orion.c | 29 +++++++++++------------------ drivers/watchdog/orion_wdt.c | 8 ++------ include/linux/io.h | 5 +++++ lib/Makefile | 2 +- lib/atomicio.c | 27 +++++++++++++++++++++++++++ 7 files changed, 79 insertions(+), 25 deletions(-) create mode 100644 lib/atomicio.c -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
