Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sat, 24 Aug 2013 22:35:34 +0200 | From | Richard Weinberger <> | Subject | Re: [PATCH v4 1/4] lib: Introduce atomic MMIO modify |
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Am 24.08.2013 21:58, schrieb Ezequiel Garcia: > On Sat, Aug 24, 2013 at 08:27:10PM +0200, richard -rw- weinberger wrote: >> On Sat, Aug 24, 2013 at 5:35 PM, Ezequiel Garcia >> <ezequiel.garcia@free-electrons.com> wrote: >>> Some platforms have MMIO regions that are shared across orthogonal >>> subsystems. This commit implements a possible solution for the >>> thread-safe access of such regions through a spinlock-protected API. >>> >>> Concurrent access is protected with a single spinlock for the >>> entire MMIO address space. While this protects shared-registers, >>> it also serializes access to unrelated/unshared registers. >>> >>> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com> >>> --- >>> include/linux/io.h | 5 +++++ >>> lib/Makefile | 2 +- >>> lib/atomicio.c | 27 +++++++++++++++++++++++++++ >>> 3 files changed, 33 insertions(+), 1 deletion(-) >>> create mode 100644 lib/atomicio.c >>> >>> diff --git a/include/linux/io.h b/include/linux/io.h >>> index f4f42fa..c331dcb 100644 >>> --- a/include/linux/io.h >>> +++ b/include/linux/io.h >>> @@ -101,4 +101,9 @@ static inline void arch_phys_wc_del(int handle) >>> #define arch_phys_wc_add arch_phys_wc_add >>> #endif >>> >>> +#ifndef __HAVE_ARCH_ATOMIC_IO_MODIFY >>> +/* Atomic MMIO-wide IO modify */ >>> +extern void atomic_io_modify(void __iomem *reg, u32 mask, u32 set); >>> +#endif >>> + >>> #endif /* _LINUX_IO_H */ >>> diff --git a/lib/Makefile b/lib/Makefile >>> index 7baccfd..695d6e2 100644 >>> --- a/lib/Makefile >>> +++ b/lib/Makefile >>> @@ -13,7 +13,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \ >>> sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \ >>> proportions.o flex_proportions.o prio_heap.o ratelimit.o show_mem.o \ >>> is_single_threaded.o plist.o decompress.o kobject_uevent.o \ >>> - earlycpio.o percpu-refcount.o >>> + earlycpio.o percpu-refcount.o atomicio.o >>> >>> obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o >>> lib-$(CONFIG_MMU) += ioremap.o >>> diff --git a/lib/atomicio.c b/lib/atomicio.c >>> new file mode 100644 >>> index 0000000..1750f9d >>> --- /dev/null >>> +++ b/lib/atomicio.c >>> @@ -0,0 +1,27 @@ >>> +#include <linux/io.h> >>> +#include <linux/spinlock.h> >>> + >>> +#ifndef __HAVE_ARCH_ATOMIC_IO_MODIFY >>> +/* >>> + * Generic atomic MMIO modify. >>> + * >>> + * Allows thread-safe access to registers shared by unrelated subsystems. >>> + * The access is protected by a single MMIO-wide lock. >>> + * >>> + * Optimized variants can be implemented on a per-architecture basis. >>> + */ >>> +static DEFINE_RAW_SPINLOCK(__io_lock); >>> +void atomic_io_modify(void __iomem *reg, u32 mask, u32 set) >>> +{ >>> + unsigned long flags; >>> + u32 value; >>> + >>> + raw_spin_lock_irqsave(&__io_lock, flags); >>> + value = readl(reg) & ~mask; >>> + value |= (set & mask); >>> + writel(value, reg); >>> + raw_spin_unlock_irqrestore(&__io_lock, flags); >>> + >>> +} >>> +EXPORT_SYMBOL(atomic_io_modify); >> >> Why not the default case EXPORT_SYMBOL_GPL()? >> > > Because I copy-pasted the export from some other lib/.. :-) > > Mind explaining me the difference, why you say _GPL it's the default, > and why EXPORT_SYMBOL is more frequently used in lib/ ?
As the kernel is GPL it is the default case to mark new things as GPL symbols. If your new feature is a core feature which is used by mostly everyone, EXPORT_SYMBOL() is appropriate. I.e. having kmalloc() and friends EXPORT_SYMBOL_GPL() would be a bad idea. :) EXPORT_SYMBOL() seems to be often used in lib/ because most lib/ things are core features.
Thanks, //richard
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