summaryrefslogtreecommitdiffstats
path: root/include/asm-generic/ticket_spinlock.h
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2026-08-19 10:09:22 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2026-08-19 10:09:22 -0700
commitf4cdf7ca9a1fdcca413157df19753f388a5a224e (patch)
tree60a31895b2446cd7fa27514e8c2843534a0de0da /include/asm-generic/ticket_spinlock.h
downloadlinux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz
linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip
Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted
Pull media updates from Mauro Carvalho Chehab: - v4l2-core: added ISP statistics support and per-block validation - v4l2-core: Allow unknown HDR10 white point and luminance - New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor - New codec: Milos: VPU v2.0 codec support - isp driver: gained support for Dreamchip RPPX1 ISP framework - vsp1 driver: gained support for RZ/T2H and RZ/N2H - Novalake driver: gained CVS support for new NVL hardware - dvb-core: fix feed leak on failed DMX_ADD_PID - several driver fixes, cleanups and minor improvements * tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits) media: ipu-bridge: check all DMI entries when overriding sensor rotation media: v4l2-async: avoid deleting unlinked ASC entry on link error media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement media: intel/ipu6: fix async notifier cleanup leak on parse error media: staging/ipu7: fix async notifier UAF on probe error path media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem() media: rcar-isp: Fix VSPX reference leaks media: rcar-isp: Release ISPCORE resources media: i2c: imx415: Release runtime PM reference on VBLANK error media: i2c: imx415: Return test pattern write errors media: renesas: vsp1: Declare index variables in for loop statement media: renesas: vsp1: Make reset control optional to support platforms without a reset line media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs media: nxp: imx8-isi: Add additional 32-bit RGB format support media: nxp: imx8-isi: Add 16-bit raw Bayer format support media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks media: nxp: imx8-isi: Correct color map between V4L2 and ISI ...
Diffstat (limited to 'include/asm-generic/ticket_spinlock.h')
-rw-r--r--include/asm-generic/ticket_spinlock.h105
1 files changed, 105 insertions, 0 deletions
diff --git a/include/asm-generic/ticket_spinlock.h b/include/asm-generic/ticket_spinlock.h
new file mode 100644
index 000000000..325779970
--- /dev/null
+++ b/include/asm-generic/ticket_spinlock.h
@@ -0,0 +1,105 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * 'Generic' ticket-lock implementation.
+ *
+ * It relies on atomic_fetch_add() having well defined forward progress
+ * guarantees under contention. If your architecture cannot provide this, stick
+ * to a test-and-set lock.
+ *
+ * It also relies on atomic_fetch_add() being safe vs smp_store_release() on a
+ * sub-word of the value. This is generally true for anything LL/SC although
+ * you'd be hard pressed to find anything useful in architecture specifications
+ * about this. If your architecture cannot do this you might be better off with
+ * a test-and-set.
+ *
+ * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence
+ * uses atomic_fetch_add() which is RCsc to create an RCsc hot path, along with
+ * a full fence after the spin to upgrade the otherwise-RCpc
+ * atomic_cond_read_acquire().
+ *
+ * The implementation uses smp_cond_load_acquire() to spin, so if the
+ * architecture has WFE like instructions to sleep instead of poll for word
+ * modifications be sure to implement that (see ARM64 for example).
+ *
+ */
+
+#ifndef __ASM_GENERIC_TICKET_SPINLOCK_H
+#define __ASM_GENERIC_TICKET_SPINLOCK_H
+
+#include <linux/atomic.h>
+#include <asm-generic/spinlock_types.h>
+
+static __always_inline void ticket_spin_lock(arch_spinlock_t *lock)
+{
+ u32 val = atomic_fetch_add(1<<16, &lock->val);
+ u16 ticket = val >> 16;
+
+ if (ticket == (u16)val)
+ return;
+
+ /*
+ * atomic_cond_read_acquire() is RCpc, but rather than defining a
+ * custom cond_read_rcsc() here we just emit a full fence. We only
+ * need the prior reads before subsequent writes ordering from
+ * smb_mb(), but as atomic_cond_read_acquire() just emits reads and we
+ * have no outstanding writes due to the atomic_fetch_add() the extra
+ * orderings are free.
+ */
+ atomic_cond_read_acquire(&lock->val, ticket == (u16)VAL);
+ smp_mb();
+}
+
+static __always_inline bool ticket_spin_trylock(arch_spinlock_t *lock)
+{
+ u32 old = atomic_read(&lock->val);
+
+ if ((old >> 16) != (old & 0xffff))
+ return false;
+
+ return atomic_try_cmpxchg(&lock->val, &old, old + (1<<16)); /* SC, for RCsc */
+}
+
+static __always_inline void ticket_spin_unlock(arch_spinlock_t *lock)
+{
+ u16 *ptr = (u16 *)lock + IS_ENABLED(CONFIG_CPU_BIG_ENDIAN);
+ u32 val = atomic_read(&lock->val);
+
+ smp_store_release(ptr, (u16)val + 1);
+}
+
+static __always_inline int ticket_spin_value_unlocked(arch_spinlock_t lock)
+{
+ u32 val = lock.val.counter;
+
+ return ((val >> 16) == (val & 0xffff));
+}
+
+static __always_inline int ticket_spin_is_locked(arch_spinlock_t *lock)
+{
+ arch_spinlock_t val = READ_ONCE(*lock);
+
+ return !ticket_spin_value_unlocked(val);
+}
+
+static __always_inline int ticket_spin_is_contended(arch_spinlock_t *lock)
+{
+ u32 val = atomic_read(&lock->val);
+
+ return (s16)((val >> 16) - (val & 0xffff)) > 1;
+}
+
+#ifndef __no_arch_spinlock_redefine
+/*
+ * Remapping spinlock architecture specific functions to the corresponding
+ * ticket spinlock functions.
+ */
+#define arch_spin_is_locked(l) ticket_spin_is_locked(l)
+#define arch_spin_is_contended(l) ticket_spin_is_contended(l)
+#define arch_spin_value_unlocked(l) ticket_spin_value_unlocked(l)
+#define arch_spin_lock(l) ticket_spin_lock(l)
+#define arch_spin_trylock(l) ticket_spin_trylock(l)
+#define arch_spin_unlock(l) ticket_spin_unlock(l)
+#endif
+
+#endif /* __ASM_GENERIC_TICKET_SPINLOCK_H */