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Daniel Vetter 99264a61df drm/vblank: Fixup and document timestamp update/read barriers 
This was a bit too much cargo-culted, so lets make it solid:
- vblank->count doesn't need to be an atomic, writes are always done
  under the protection of dev->vblank_time_lock. Switch to an unsigned
  long instead and update comments. Note that atomic_read is just a
  normal read of a volatile variable, so no need to audit all the
  read-side access specifically.

- The barriers for the vblank counter seqlock weren't complete: The
  read-side was missing the first barrier between the counter read and
  the timestamp read, it only had a barrier between the ts and the
  counter read. We need both.

- Barriers weren't properly documented. Since barriers only work if
  you have them on boths sides of the transaction it's prudent to
  reference where the other side is. To avoid duplicating the
  write-side comment 3 times extract a little store_vblank() helper.
  In that helper also assert that we do indeed hold
  dev->vblank_time_lock, since in some cases the lock is acquired a
  few functions up in the callchain.

Spotted while reviewing a patch from Chris Wilson to add a fastpath to
the vblank_wait ioctl.

v2: Add comment to better explain how store_vblank works, suggested by
Chris.

v3: Peter noticed that as-is the 2nd smp_wmb is redundant with the
implicit barrier in the spin_unlock. But that can only be proven by
auditing all callers and my point in extracting this little helper was
to localize all the locking into just one place. Hence I think that
additional optimization is too risky.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Michel Dänzer <michel@daenzer.net>
Cc: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-and-tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
2015-05-04 10:57:00 +02:00
..
accessibility
acpi Revert "x86/PCI: Refine the way to release PCI IRQ resources" 2015-03-20 14:56:19 +01:00
amba ARM: 8256/1: driver coamba: add device binding path 'driver_override' 2015-02-10 10:23:15 +00:00
android android: binder: fix binder mmap failures 2015-03-01 18:43:51 -08:00
ata ata: Add a new flag to destinguish sas controller 2015-03-19 14:14:43 -04:00
atm
auxdisplay
base regmap: Fix for v4.0 2015-03-24 16:42:54 -07:00
bcma bcma: implement host code support for PCIe Gen 2 devices 2015-01-29 10:54:43 +02:00
block NVMe: Initialize device list head before starting 2015-03-23 09:35:12 -06:00
bluetooth Bluetooth: btusb: Fix issue with CSR based Intel Wireless controllers 2015-02-23 09:30:35 +02:00
bus ARM: SoC platform changes 2015-02-17 09:27:54 -08:00
cdrom
char Not entirely surprising: the ongoing QEMU work on virtio 1.0 has revealed 2015-03-17 10:36:01 -07:00
clk The clk fixes for 4.0-rc4 comprise three themes. First are the usual 2015-03-15 15:07:08 -07:00
clocksource clocksource/drivers/sun5i: Fix cpufreq interaction with sched_clock() 2015-03-26 10:59:40 +01:00
connector
coresight coresight: fix function etm_writel_cp14() parameter order 2015-02-04 10:42:55 -08:00
cpufreq Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/evalenti/linux-soc-thermal 2015-03-06 13:43:33 -08:00
cpuidle cpuidle: mvebu: Update cpuidle thresholds for Armada XP SOCs 2015-03-13 18:31:29 +01:00
crypto Merge branch 'for-linus' of git://git.infradead.org/users/vkoul/slave-dma 2015-02-18 08:49:20 -08:00
dca
devfreq Merge branches 'pm-cpufreq', 'pm-cpuidle', 'pm-devfreq', 'pm-opp' and 'pm-tools' 2015-02-13 21:39:06 +01:00
dio
dma dmaengine: pl08x: Define capabilities for generic capabilities reporting 2015-03-18 21:34:29 +05:30
dma-buf
edac * A fix to sb_edac for proper detection on SNB machines 2015-02-19 11:18:14 -08:00
eisa
extcon extcon: max77693: Constify struct regmap_config 2015-01-26 13:47:55 +09:00
firewire firewire: core: use correct vendor/model IDs 2015-02-02 21:56:03 +01:00
firmware * Fix regression in DMI sysfs code for handling "End of Table" entry 2015-03-02 14:18:57 +01:00
fmc
gpio gpio: tps65912: fix wrong container_of arguments 2015-02-23 15:40:32 +01:00
gpu drm/vblank: Fixup and document timestamp update/read barriers 2015-05-04 10:57:00 +02:00
hid HID: wacom: check for wacom->shared before following the pointer 2015-03-17 20:59:55 +01:00
hsi
hv Char / Misc patches for 3.20-rc1 2015-02-15 10:48:44 -08:00
hwmon hwmon: (ads7828) Check return value of devm_regmap_init_i2c 2015-02-22 20:10:30 -08:00
hwspinlock
i2c Revert "i2c: core: Dispose OF IRQ mapping at client removal time" 2015-03-12 10:23:05 +01:00
ide ide_tape: convert jiffies with jiffies_to_msecs 2015-03-18 23:25:57 -04:00
idle intel_idle: Add ->enter_freeze callbacks 2015-02-15 19:40:09 +01:00
iio Second round of IIO fixes for the 4.0 cycle (or round one part two really!) 2015-02-28 07:19:27 -08:00
infiniband IB/mlx4: Saturate RoCE port PMA counters in case of overflow 2015-03-18 15:17:11 -04:00
input Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2015-03-19 16:43:10 -07:00
iommu iommu/io-pgtable-arm: Add built time dependency 2015-03-03 14:04:12 +01:00
ipack
irqchip Merge branch 'irqchip/urgent-gic' into irqchip/urgent 2015-03-15 01:41:26 +00:00
isdn isdn: icn: use strlcpy() when parsing setup options 2015-03-15 22:24:37 -04:00
leds leds: leds-gpio: Pass on error codes unmodified 2015-02-02 14:36:10 -08:00
lguest OK, this has the big virtio 1.0 implementation, as specified by OASIS. 2015-02-18 09:24:01 -08:00
macintosh
mailbox Merge branch 'mailbox-devel' of git://git.linaro.org/landing-teams/working/fujitsu/integration 2015-02-11 12:56:40 -08:00
mcb mcb: Fix error path of mcb_pci_probe 2015-02-03 15:48:51 -08:00
md . Fix DM core device cleanup regression -- due to a latent race that was 2015-03-26 14:53:47 -07:00
media mm: gup: use get_user_pages_unlocked 2015-02-11 17:06:05 -08:00
memory memory/fsl-corenet-cf: Add t1040 support 2015-01-29 22:57:43 -06:00
memstick
message i2o: move to staging 2015-02-03 15:58:39 -08:00
mfd mfd: kempld-core: Fix callback return value check 2015-03-12 09:27:58 +00:00
misc mei: make device disabled on stop unconditionally 2015-03-01 19:34:50 -08:00
mmc mmc: pwrseq_simple: fix error path in mmc_pwrseq_simple_alloc 2015-03-19 11:26:35 +01:00
mtd This pull request fixes a bug introduced during the v4.0 merge window where we 2015-03-21 10:36:44 -07:00
net cx82310_eth: wait for firmware to become ready 2015-03-21 18:23:19 -04:00
nfc NFC: nci: Move NFCEE discovery logic 2015-02-04 09:15:18 +01:00
ntb
nubus
of Revert "of: Fix premature bootconsole disable with 'stdout-path'" 2015-03-19 08:46:54 -05:00
oprofile
parisc
parport
pci PCI updates for v4.0: 2015-03-12 09:45:46 -07:00
pcmcia Revert "pcmcia: add a new resource manager for non ISA systems" 2015-03-11 14:21:23 +01:00
phy phy: omap-usb2: Fix missing clk_prepare call when using old dt name 2015-03-13 17:14:39 +05:30
pinctrl pinctrl: sun4i: GPIOs configured as irq must be set to input before reading 2015-03-18 10:56:46 +01:00
platform Merge branch 'x86-platform-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-02-21 11:12:07 -08:00
pnp Merge branches 'pnp', 'pm-cpuidle' and 'pm-cpufreq' 2015-02-21 04:29:16 +01:00
power power_supply: 88pm860x: Fix leaked power supply on probe fail 2015-01-28 15:08:10 +01:00
powercap powercap / RAPL: handle domains with different energy units 2015-03-13 23:18:44 +01:00
pps
ps3
ptp
pwm pwm: tegra: Use NSEC_PER_SEC 2015-02-18 08:40:29 +01:00
rapidio Merge branch 'for-linus' of git://git.infradead.org/users/vkoul/slave-dma 2015-02-18 08:49:20 -08:00
ras
regulator Merge remote-tracking branches 'regulator/fix/doc' and 'regulator/fix/palmas' into regulator-linus 2015-03-23 11:43:42 -07:00
remoteproc
reset
rpmsg virtio_rpmsg: set DRIVER_OK before using device 2015-03-13 15:55:42 +10:30
rtc drivers/rtc/rtc-mrst: fix suspend/resume 2015-03-25 16:20:30 -07:00
s390 s390/dcss: array index 'i' is used before limits check. 2015-02-26 09:24:48 +01:00
sbus
scsi Merge branch 'for-4.0-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata 2015-03-24 17:08:29 -07:00
sfi
sh drivers: sh: Disable PM runtime for multi-platform r8a7740 with genpd 2015-02-24 07:26:12 +09:00
sn
soc ARM: SoC driver updates 2015-02-17 09:38:59 -08:00
spi Merge remote-tracking branches 'spi/fix/dw', 'spi/fix/queue' and 'spi/fix/qup' into spi-linus 2015-03-24 10:38:44 -07:00
spmi
ssb treewide: Remove unnecessary SSB_DEVTABLE_END macro 2015-02-11 14:38:29 -08:00
staging vt6655: Fix late setting of byRFType. 2015-03-09 11:33:13 +01:00
target target: do not reject FUA CDBs when write cache is enabled but emulate_write_cache is 0 2015-03-19 23:26:46 -07:00
tc
thermal thermal: Make sysfs attributes of cooling devices default attributes 2015-03-05 01:47:57 -04:00
thunderbolt
tty serial: 8250_dw: Fix deadlock in LCR workaround 2015-03-11 16:39:52 +01:00
uio
usb USB / PHY driver fixes for 4.0-rc5 2015-03-22 11:33:55 -07:00
uwb USB patches for 3.20-rc1 2015-02-15 10:24:55 -08:00
vfio vfio-pci: Add missing break to enable VFIO_PCI_ERR_IRQ_INDEX 2015-03-12 09:51:38 -06:00
vhost Merge git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending 2015-03-21 11:24:38 -07:00
video OMAPDSS: fix regression with display sysfs files 2015-02-26 10:23:15 +02:00
virt
virtio virtio_mmio: fix access width for mmio 2015-03-17 12:12:21 +10:30
vlynq
vme
w1
watchdog watchdog: imgpdc: Fix default heartbeat 2015-03-27 08:47:50 +01:00
xen Merge git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending 2015-03-21 11:24:38 -07:00
zorro
Kconfig i2o: move to staging 2015-02-03 15:58:39 -08:00
Makefile