- 19 5月, 2012 4 次提交
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由 Grant Likely 提交于
This patch changes the of_xlate API to make it possible for multiple gpio_chips to refer to the same device tree node. This is useful for banked GPIO controllers that use multiple gpio_chips for a single device. With this change the core code will try calling of_xlate on each gpio_chip that references the device_node and will return the gpio number for the first one to return 'true'. Tested-by: NRoland Stigge <stigge@antcom.de> Acked-by: NArnd Bergmann <arnd@arndb.de> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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由 Mark Brown 提交于
Allow drivers to use the modern request and configure idiom together with devres. As with plain gpio_request() and gpio_request_one() we can't implement the old school version in terms of _one() as this would force the explicit selection of a direction in gpio_request() which could break systems if we pick the wrong one. Implementing devm_gpio_request_one() in terms of devm_gpio_request() would needlessly complicate things or lead to duplication from the unmanaged version depending on how it's done. Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com> Acked-by: NLinus Walleij <linus.walleij@linaro.org> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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由 Peter Korsgaard 提交于
Pullups are enabled when bits are set, not when cleared. Signed-off-by: NPeter Korsgaard <jacmet@sunsite.dk> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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由 Andreas Schallenberg 提交于
This patch extends the PCA953x driver to support TI's TCA6424A 24 bit I2C I/O expander. The patch is based on code by Michele Bevilacqua. Changes in v2: - Compare ngpio against 24 in both places, not >16 - Larger datatype now u32 instead of uint. Bit fields not used for struct members since their address is taken. - Be precise: TCA6424A (untested for older TCA6424) Signed-off-by: Andreas Schallenberg<Andreas.Schallenberg@3alitytechnica.com> Acked-by: NLinus Walleij <linus.walleij@linaro.org> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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- 12 5月, 2012 12 次提交
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由 Grant Likely 提交于
Merge branch 'for_3.5/gpio/cleanup' of git://git.kernel.org/pub/scm/linux/kernel/git/khilman/linux-omap-pm into gpio/next
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由 Tarun Kanti DebBarma 提交于
We do checking for bank->enabled_non_wakeup_gpios in order to skip redundant operations. Somehow, the check got missed while doing the cleanup series. Just to make sure that we do context restore correctly in *_runtime_resume(), the bank->workaround_enabled check is moved after context restore. Otherwise, it would prevent context restore when bank->enabled_non_wakeup_gpios is 0. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
Add register offsets for GPIO_IRQSTATUS_RAW_0, GPIO_IRQSTATUS_RAW_0 which are present on OMAP4+ processors. Now we can distinguish conditions applicable to OMAP4,5 and those specific to OMAP24xx and OMAP3xxx. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
Both omap_gpio_suspend() and omap_gpio_resume() does programming of wakeup_en register. _gpio_rmw(base, bank->regs->wkup_en, 0xffffffff, 0); _gpio_rmw(base, bank->regs->wkup_en, bank->context.wake_en, 1); This is redundant in omap_gpio_suspend() because wakeup_en register automatically gets initialized in _set_gpio_wakeup() and set_gpio_trigger() while being called either from chip.irq_set_wake() or chip.irq_set_type(). This is also redundant in omap_gpio_resume() because wakeup_en register is programmed in omap_gpio_restore_context() called which is called from runtime resume callback. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
commit 672e302e (ARM: OMAP: use edge/level handlers from generic IRQ framework) removed retrigger support in favor of using generic IRQ framework. This patch cleans up some unused remnants of that removal. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Acked-by: NFelipe Balbi <balbi@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
There is no more need to have saved_wakeup because bank->context.wake_en already holds that value. So getting rid of read/write operation associated with this field. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Acked-by: NFelipe Balbi <balbi@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
Since we already have bank->context.wake_en to keep track of gpios which are wakeup enabled, there is no need to have this field any more. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Acked-by: NFelipe Balbi <balbi@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
Since we already have context.fallingdetect and context.risingdetect there is no more need to have these additional fields. Also, getting rid of extra reads associated with them. Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Acked-by: NFelipe Balbi <balbi@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Tarun Kanti DebBarma 提交于
This cleanup got missed while implementing following: 25db711d gpio/omap: Fix IRQ handling for SPARSE_IRQ 384ebe1c gpio/omap: Add DT support to GPIO driver Cc: Kevin Hilman <khilman@ti.com> Cc: Tony Lindgren <tony@atomide.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Cousson, Benoit <b-cousson@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Reviewed-by: NSantosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: NGovindraj.R <govindraj.raja@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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由 Mark Brown 提交于
Rather than requiring architectures that use gpiolib but don't have any need to define anything custom to copy an asm/gpio.h provide a Kconfig symbol which architectures must select in order to include gpio.h and for other architectures just provide the trivial implementation directly. This makes it much easier to do gpiolib updates and is also a step towards making gpiolib APIs available on every architecture. For architectures with existing boilerplate code leave a stub header in place which warns on direct inclusion of asm/gpio.h and includes linux/gpio.h to catch code that's doing this. Direct inclusion of asm/gpio.h has long been deprecated. Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com> Acked-by: NJonas Bonn <jonas@southpole.se> Acked-by: NTony Luck <tony.luck@intel.com> Acked-by: NLinus Walleij <linus.walleij@linaro.org> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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由 Mathias Nyman 提交于
Add gpio support for Intel MSIC chips found in Intel Medfield platforms. MSIC supports totally 24 GPIOs with 16 low voltage and 8 high voltage pins. Driver uses MSIC mfd interface for MSIC access. (Updated comment to indicate why locking is actually safe) Signed-off-by: NMathias Nyman <mathias.nyman@linux.intel.com> Signed-off-by: NAlan Cox <alan@linux.intel.com> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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由 Olof Johansson 提交于
Only code move, no functional change. Main reason to do this was to get rid of the warnings: drivers/gpio/gpio-samsung.c: In function 'samsung_gpiolib_init': drivers/gpio/gpio-samsung.c:2974:1: warning: label 'err_ioremap4' defined but not used [-Wunused-label] drivers/gpio/gpio-samsung.c:2722:47: warning: unused variable 'gpio_base4' [-Wunused-variable] without adding more ifdef mess. I think this whole file would do well being coverted over to a platform driver and moving most of the tables out to SoC code and/or device trees, but since that changes init ordering it needs to be done with some care, i.e. not at this time. Signed-off-by: NOlof Johansson <olof@lixom.net> Acked-by: NKukjin Kim <kgene.kim@samsung.com> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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- 11 5月, 2012 1 次提交
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由 Mika Westerberg 提交于
The IRQ status register should be re-read after each iteration. Otherwise the loop misses the interrupt if it gets raised immediately after handled. Reported-by: NGrant Likely <grant.likely@secretlab.ca> Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com> Acked-by: NLinus Walleij <linus.walleij@linaro.org> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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- 10 5月, 2012 1 次提交
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由 Tarun Kanti DebBarma 提交于
Initialization of irqenable, irqstatus registers is the common operation done in this function for all OMAP platforms, viz. OMAP1, OMAP2+. The latter _gpio_rmw()'s which supposedly got introduced wrongly to take care of OMAP2+ platforms were overwriting initially programmed OMAP1 value breaking functionality on OMAP1. Somehow incorrect assumption was made that each _gpio_rmw()'s were mutually exclusive. On close observation it is found that the first _gpio_rmw() which is supposedly done to take care of OMAP1 platform is generic enough and takes care of OMAP2+ platform as well. Therefore remove the latter _gpio_rmw() to irqenable as they are redundant now. Writing to ctrl and debounce_en registers for OMAP2+ platforms are modified to match the original(pre-cleanup) code where the registers are initialized with 0. In the cleanup series since we are using _gpio_rmw(reg, 0, 1), instead of __raw_writel(), we are just reading and writing the same values to ctrl and debounce_en. This is not an issue for debounce_en register because it has 0x0 as the default value. But in the case of ctrl register the default value is 0x2 (GATINGRATIO = 0x1) so that we end up writing 0x2 instead of intended 0 value. Therefore changing back to __raw_writel() as this is sufficient for this case besides simpler to understand. Also, change irqstatus initalization logic that avoids comparison with bool, besides making it fit in a single line. Cc: stable@vger.kernel.org Cc: Tony Lindgren <tony@atomide.com> Cc: Kevin Hilman <khilman@ti.com> Cc: Santosh Shilimkar <santosh.shilimkar@ti.com> Cc: Grant Likely <grant.likely@secretlab.ca> Reported-by: NJanusz Krzysztofik <jkrzyszt@tis.icnet.pl> Tested-by: NJanusz Krzysztofik <jkrzyszt@tis.icnet.pl> Signed-off-by: NTarun Kanti DebBarma <tarun.kanti@ti.com> Signed-off-by: NKevin Hilman <khilman@ti.com>
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- 09 5月, 2012 2 次提交
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由 Mika Westerberg 提交于
irq_domain already provides a facility to translate from hardware IRQ numbers to Linux IRQ numbers so use that instead of open-coding the logic in the driver. Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com> Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
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由 Grant Likely 提交于
Linux 3.4-rc6
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- 07 5月, 2012 4 次提交
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由 Linus Torvalds 提交于
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip由 Linus Torvalds 提交于
Pull x86 fixes form Peter Anvin * 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: intel_mid_powerbtn: mark irq as IRQF_NO_SUSPEND arch/x86/platform/geode/net5501.c: change active_low to 0 for LED driver x86, relocs: Remove an unused variable asm-generic: Use __BITS_PER_LONG in statfs.h x86/amd: Re-enable CPU topology extensions in case BIOS has disabled it
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git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs由 Linus Torvalds 提交于
Pull btrfs fixes from Chris Mason: "The big ones here are a memory leak we introduced in rc1, and a scheduling while atomic if the transid on disk doesn't match the transid we expected. This happens for corrupt blocks, or out of date disks. It also fixes up the ioctl definition for our ioctl to resolve logical inode numbers. The __u32 was a merging error and doesn't match what we ship in the progs." * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs: Btrfs: avoid sleeping in verify_parent_transid while atomic Btrfs: fix crash in scrub repair code when device is missing btrfs: Fix mismatching struct members in ioctl.h Btrfs: fix page leak when allocing extent buffers Btrfs: Add properly locking around add_root_to_dirty_list
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由 Al Viro 提交于
Setting TIF_IA32 in load_aout_binary() used to be enough; these days TASK_SIZE is controlled by TIF_ADDR32 and that one doesn't get set there. Switch to use of set_personality_ia32()... Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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- 06 5月, 2012 6 次提交
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由 Chris Mason 提交于
verify_parent_transid needs to lock the extent range to make sure no IO is underway, and so it can safely clear the uptodate bits if our checks fail. But, a few callers are using it with spinlocks held. Most of the time, the generation numbers are going to match, and we don't want to switch to a blocking lock just for the error case. This adds an atomic flag to verify_parent_transid, and changes it to return EAGAIN if it needs to block to properly verifiy things. Signed-off-by: NChris Mason <chris.mason@oracle.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/mattst88/alpha由 Linus Torvalds 提交于
Pull alpha fixes from Matt Turner: "My alpha tree is back up (after taking quite some time to get my GPG key signed). It contains just some simple fixes." * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mattst88/alpha: alpha: silence 'const' warning in sys_marvel.c alpha: include module.h to fix modpost on Tsunami alpha: properly define get/set_rtc_time on Marvel/SMP alpha: VGA_HOSE depends on VGA_CONSOLE
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由 Jiri Slaby 提交于
The test in pdc_console_tty_close '!tty->count' was always wrong because tty->count is decremented after tty->ops->close is called and thus can never be zero. Hence the 'then' branch was never executed and the timer never deleted. This did not matter until commit 5dd5bc40 ("TTY: pdc_cons, use tty_port"). There we needed to set TTY in tty_port to NULL, but this never happened due to the bug above. So change the test to really trigger at the last close by changing the condition to 'tty->count == 1'. Well, the driver should not touch tty->count at all. It should use tty_port->count and count open count there itself. Signed-off-by: NJiri Slaby <jslaby@suse.cz> Reported-and-tested-by: NMikulas Patocka <mpatocka@redhat.com> Cc: Kyle McMartin <kyle@mcmartin.ca> Cc: Helge Deller <deller@gmx.de> Cc: "James E.J. Bottomley" <jejb@parisc-linux.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound由 Linus Torvalds 提交于
Pull sound sound fixes from Takashi Iwai: "As good as nothing exciting here; just a few trivial fixes for various ASoC stuff." * tag 'sound-3.4' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound: ASoC: omap-pcm: Free dma buffers in case of error. ASoC: s3c2412-i2s: Fix dai registration ASoC: wm8350: Don't use locally allocated codec struct ASoC: tlv312aic23: unbreak resume ASoC: bf5xx-ssm2602: Set DAI format ASoC: core: check of_property_count_strings failure ASoC: dt: sgtl5000.txt: Add description for 'reg' field ASoC: wm_hubs: Make sure we don't disable differential line outputs
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git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux由 Linus Torvalds 提交于
Pull an ACPI patch from Len Brown: "It fixes a D3 issue new in 3.4-rc1." By Lin Ming via Len Brown: * 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux: ACPI: Fix D3hot v D3cold confusion
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由 Sasha Levin 提交于
Currently, we'll try mounting any device who's major device number is UNNAMED_MAJOR as NFS root. This would happen for non-NFS devices as well (such as 9p devices) but it wouldn't cause any issues since mounting the device as NFS would fail quickly and the code proceeded to doing the proper mount: [ 101.522716] VFS: Unable to mount root fs via NFS, trying floppy. [ 101.534499] VFS: Mounted root (9p filesystem) on device 0:18. Commit 6829a048102a ("NFS: Retry mounting NFSROOT") introduced retries when mounting NFS root, which means that now we don't immediately fail and instead it takes an additional 90+ seconds until we stop retrying, which has revealed the issue this patch fixes. This meant that it would take an additional 90 seconds to boot when we're not using a device type which gets detected in order before NFS. This patch modifies the NFS type check to require device type to be 'Root_NFS' instead of requiring the device to have an UNNAMED_MAJOR major. This makes boot process cleaner since we now won't go through the NFS mounting code at all when the device isn't an NFS root ("/dev/nfs"). Signed-off-by: NSasha Levin <levinsasha928@gmail.com> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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- 05 5月, 2012 10 次提交
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由 Takashi Iwai 提交于
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git://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound由 Takashi Iwai 提交于
ASoC: Updates for 3.4 Nothing terribly exciting here, a bunch of small and simple fixes scattered around the place.
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由 Lin Ming 提交于
Before this patch, ACPI_STATE_D3 incorrectly referenced D3hot in some places, but D3cold in other places. After this patch, ACPI_STATE_D3 always means ACPI_STATE_D3_COLD; and all references to D3hot use ACPI_STATE_D3_HOT. ACPI's _PR3 method is used to enter both D3hot and D3cold states. What distinguishes D3hot from D3cold is the presence _PR3 (Power Resources for D3hot) If these resources are all ON, then the state is D3hot. If _PR3 is not present, or all _PR0 resources for the devices are OFF, then the state is D3cold. This patch applies after Linux-3.4-rc1. A future syntax cleanup may remove ACPI_STATE_D3 to emphasize that it always means ACPI_STATE_D3_COLD. Signed-off-by: NLin Ming <ming.m.lin@intel.com> Acked-by: NRafael J. Wysocki <rjw@sisk.pl> Reviewed-by: NAaron Lu <aaron.lu@amd.com> Signed-off-by: NLen Brown <len.brown@intel.com>
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由 Greg Kroah-Hartman 提交于
Commit ec81aecb ("hfs: fix a potential buffer overflow") fixed a few potential buffer overflows in the hfs filesystem. But as Timo Warns pointed out, these changes also need to be made on the hfsplus filesystem as well. Reported-by: NTimo Warns <warns@pre-sense.de> Acked-by: NWANG Cong <amwang@redhat.com> Cc: Alexey Khoroshilov <khoroshilov@ispras.ru> Cc: Miklos Szeredi <mszeredi@suse.cz> Cc: Sage Weil <sage@newdream.net> Cc: Eugene Teo <eteo@redhat.com> Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Dave Anderson <anderson@redhat.com> Cc: stable <stable@vger.kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip由 Linus Torvalds 提交于
Pull timer fix from Thomas Gleixner. * 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: rtc: Fix possible null pointer dereference in rtc-mpc5121.c
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git://git.samba.org/sfrench/cifs-2.6由 Linus Torvalds 提交于
Pull CIFS fixes from Steve French. * git://git.samba.org/sfrench/cifs-2.6: fs/cifs: fix parsing of dfs referrals cifs: make sure we ignore the credentials= and cred= options [CIFS] Update cifs version to 1.78 cifs - check S_AUTOMOUNT in revalidate cifs: add missing initialization of server->req_lock cifs: don't cap ra_pages at the same level as default_backing_dev_info CIFS: Fix indentation in cifs_show_options
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由 Dave Jones 提交于
Remove myself as cpufreq maintainer. x86 driver changes can go through the regular x86/ACPI trees. ARM driver changes through the ARM trees. cpufreq core changes are rare these days, and can just go to lkml/direct. Signed-off-by: NDave Jones <davej@redhat.com> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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由 Linus Torvalds 提交于
The normal read_seqcount_begin() function will wait for any current writers to exit their critical region by looping until the sequence count is even. That "wait for sequence count to stabilize" is the right thing to do if the read-locker will just retry the whole operation on contention: no point in doing a potentially expensive reader sequence if we know at the beginning that we'll just end up re-doing it all. HOWEVER. Some users don't actually retry the operation, but instead will abort and do the operation with proper locking. So the sequence count case may be the optimistic quick case, but in the presense of writers you may want to do full locking in order to guarantee forward progress. The prime example of this would be the RCU name lookup. And in that case, you may well be better off without the "retry early", and are in a rush to instead get to the failure handling. Thus this "raw" interface that just returns the sequence number without testing it - it just forces the low bit to zero so that read_seqcount_retry() will always fail such a "active concurrent writer" scenario. Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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由 Linus Torvalds 提交于
We really need to use a ACCESS_ONCE() on the sequence value read in __read_seqcount_begin(), because otherwise the compiler might end up reloading the value in between the test and the return of it. As a result, it might end up returning an odd value (which means that a write is in progress). If the reader is then fast enough that that odd value is still the current one when the read_seqcount_retry() is done, we might end up with a "successful" read sequence, even despite the concurrent write being active. In practice this probably never really happens - there just isn't anything else going on around the read of the sequence count, and the common case is that we end up having a read barrier immediately afterwards. So the code sequence in which gcc might decide to reaload from memory is small, and there's no reason to believe it would ever actually do the reload. But if the compiler ever were to decide to do so, it would be incredibly annoying to debug. Let's just make sure. Cc: stable@kernel.org Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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