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Add missing linking regulator node to usb bus for power usb devices.
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
[ khilman: minor typo fixup ]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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As per the schematic Monolithic Power Systems MP2161GJ-C499
supply a fixed output voltage of 5.0V. This supplies linked
to VDD_EE, HDMI_P5V0, USB_POWER, VCCK, VDDIO_AO1V8, VDDIO_AO3V3,
VDD3V3, DDR3_1V5 according to the schematics.
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The Ugoos AM6 is based on the Amlogic W400 (G12B) reference design using the
S922X chipset. Hardware specifications:
- 2GB LPDDR4 RAM
- 16GB eMMC storage
- 10/100/1000 Base-T Ethernet using External RGMII PHY
- 802.11 a/b/g/b/ac + BT 5.0 sdio wireless (Ampak 6398S)
- HDMI 2.0 (4k@60p) video
- Composite video + 2-channel audio output on 3.5mm jack
- S/PDIF audio output
- Aux input
- 1x USB 3.0
- 3x USB 2.0
- 1x micro SD card slot
The device-tree is largely based on meson-g12b-odroid-n2 but with audio
and USB config copied from meson-g12a-x96-max.
Tested-by: Oleg Ivanov <balbes-150@yandex.ru>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The Ugoos AM6 is based on the Amlogic W400 (G12B) reference design using the
S922X chipset.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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Ugoos Industrial Co., Ltd. are a manufacturer of ARM based TV Boxes/Dongles,
Digital Signage and Advertisement Solutions [0].
[0] (https://ugoos.com)
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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Meson G12B SoCs (S922X and A311D) are a big-little design where not all CPUs
are equal; the A53s cores are weaker than the A72s.
Include capacity-dmips-mhz properties to tell the OS there is a difference
in processing capacity. The dmips values are based on similar submissions for
other A53/A72 SoCs: HiSilicon 3660 [1] and Rockchip RK3399 [2].
This change is particularly beneficial for use-cases like retro gaming where
emulators often run on a single core. The OS now chooses an A72 core instead
of an A53 core.
[1] https://lore.kernel.org/patchwork/patch/862742/
[2] https://patchwork.kernel.org/patch/10836577/
Signed-off-by: Frank Hartung <supervisedthinking@gmail.com>
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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Add basic support for the Amlogic A1 based Amlogic AD401 board:
which describe components as follows: Reserve Memory, CPU, GIC, IRQ,
Timer, UART. It's capable of booting up into the serial console.
Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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Add the compatible for the Amlogic A1 Based AD401 board.
Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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Add bindings for the new Amlogic A1 SoC family.
A1 is an application processor designed for smart audio and IoT applications,
with dual core Cortex-A35.
Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The VIM3 on-board MCU can mux the PCIe/USB3.0 shared differential
lines using a FUSB340TMX USB 3.1 SuperSpeed Data Switch between
an USB3.0 Type A connector and a M.2 Key M slot.
The PHY driving these differential lines is shared between
the USB3.0 controller and the PCIe Controller, thus only
a single controller can use it.
The needed DT configuration when the MCU is configured to mux
the PCIe/USB3.0 differential lines to the M.2 Key M slot is
added commented and may be uncommented to disable USB3.0 from the
USB Complex and enable the PCIe controller.
The End User is not expected to uncomment the following except for
testing purposes, but instead rely on the firmware/bootloader to
update these nodes accordingly if PCIe mode is selected by the MCU.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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This adds the Amlogic G12A PCI Express controller node, also
using the USB3+PCIe Combo PHY.
The PHY mode selection is static, thus the USB3+PCIe Combo PHY
phandle would need to be removed from the USB control node if the
shared differential lines are used for PCIe instead of USB3.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The former is going to use the latter to retrieve the efuses data.
Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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SDIO node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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SDIO node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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in SDIO node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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SDIO node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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node
The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The WiFi firmware requires that the power is kept enabled while in
suspend mode. Add the keep-power-in-suspend property in the SDIO node
to specify that the power must be kept when entering in a system wide
suspend state.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The base address of the audio bus and pdm device are different
between the g12 and sm1 SoC families. Overwriting the reg property
only would leave with confusing node names on the sm1.
Move the audio related devices to the g12 dtsi. The appropriate nodes
will be created for the sm1 later on.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The power domain declared in the g12a and g12b dtsi are the same.
Move the declaration of these power domains in the g12 common dtsi.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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While the sm1 is very close to the g12a/b family, somethings apply
differently on the g12a/b and not the sm1. This introduce a new layer
of dtsi for part which apply to the g12a and g12b but not the sm1.
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The register region size initially is too small to access all
the fifo registers.
Fixes: c59b7fe5aafd ("arm64: dts: meson: g12a: add audio fifos")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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The register region size initially is too small to access all
the fifo registers.
Fixes: f2b8f6a93357 ("arm64: dts: meson-axg: add audio fifos")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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Set the appropriate gpio interrupt controller compatible for the
sm1 SoC family. This newer version of the controller can now
trig irq on both edge of the input signal
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
Pull btrfs fixes from David Sterba:
"A bunch of fixes that accumulated in recent weeks, mostly material for
stable.
Summary:
- fix for regression from 5.3 that prevents to use balance convert
with single profile
- qgroup fixes: rescan race, accounting leak with multiple writers,
potential leak after io failure recovery
- fix for use after free in relocation (reported by KASAN)
- other error handling fixups"
* tag 'for-5.4-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
btrfs: qgroup: Fix reserved data space leak if we have multiple reserve calls
btrfs: qgroup: Fix the wrong target io_tree when freeing reserved data space
btrfs: Fix a regression which we can't convert to SINGLE profile
btrfs: relocation: fix use-after-free on dead relocation roots
Btrfs: fix race setting up and completing qgroup rescan workers
Btrfs: fix missing error return if writeback for extent buffer never started
btrfs: adjust dirty_metadata_bytes after writeback failure of extent buffer
Btrfs: fix selftests failure due to uninitialized i_mode in test inodes
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Pull csky updates from Guo Ren:
"This round of csky subsystem just some fixups:
- Fix mb() synchronization problem
- Fix dma_alloc_coherent with PAGE_SO attribute
- Fix cache_op failed when cross memory ZONEs
- Optimize arch_sync_dma_for_cpu/device with dma_inv_range
- Fix ioremap function losing
- Fix arch_get_unmapped_area() implementation
- Fix defer cache flush for 610
- Support kernel non-aligned access
- Fix 610 vipt cache flush mechanism
- Fix add zero_fp fixup perf backtrace panic
- Move static keyword to the front of declaration
- Fix csky_pmu.max_period assignment
- Use generic free_initrd_mem()
- entry: Remove unneeded need_resched() loop"
* tag 'csky-for-linus-5.4-rc1' of git://github.com/c-sky/csky-linux:
csky: Move static keyword to the front of declaration
csky: entry: Remove unneeded need_resched() loop
csky: Fixup csky_pmu.max_period assignment
csky: Fixup add zero_fp fixup perf backtrace panic
csky: Use generic free_initrd_mem()
csky: Fixup 610 vipt cache flush mechanism
csky: Support kernel non-aligned access
csky: Fixup defer cache flush for 610
csky: Fixup arch_get_unmapped_area() implementation
csky: Fixup ioremap function losing
csky: Optimize arch_sync_dma_for_cpu/device with dma_inv_range
csky/dma: Fixup cache_op failed when cross memory ZONEs
csky: Fixup dma_alloc_coherent with PAGE_SO attribute
csky: Fixup mb() synchronization problem
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git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc
Pull ARM SoC fixes from Olof Johansson:
"A few fixes that have trickled in through the merge window:
- Video fixes for OMAP due to panel-dpi driver removal
- Clock fixes for OMAP that broke no-idle quirks + nfsroot on DRA7
- Fixing arch version on ASpeed ast2500
- Two fixes for reset handling on ARM SCMI"
* tag 'armsoc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc:
ARM: aspeed: ast2500 is ARMv6K
reset: reset-scmi: add missing handle initialisation
firmware: arm_scmi: reset: fix reset_state assignment in scmi_domain_reset
bus: ti-sysc: Remove unpaired sysc_clkdm_deny_idle()
ARM: dts: logicpd-som-lv: Fix i2c2 and i2c3 Pin mux
ARM: dts: am3517-evm: Fix missing video
ARM: dts: logicpd-torpedo-baseboard: Fix missing video
ARM: omap2plus_defconfig: Fix missing video
bus: ti-sysc: Fix handling of invalid clocks
bus: ti-sysc: Fix clock handling for no-idle quirks
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git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing fixes from Steven Rostedt:
"A few more tracing fixes:
- Fix a buffer overflow by checking nr_args correctly in probes
- Fix a warning that is reported by clang
- Fix a possible memory leak in error path of filter processing
- Fix the selftest that checks for failures, but wasn't failing
- Minor clean up on call site output of a memory trace event"
* tag 'trace-v5.4-3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
selftests/ftrace: Fix same probe error test
mm, tracing: Print symbol name for call_site in trace events
tracing: Have error path in predicate_parse() free its allocated memory
tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro
tracing/probe: Fix to check the difference of nr_args before adding probe
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Pull more MMC updates from Ulf Hansson:
"A couple more updates/fixes for MMC:
- sdhci-pci: Add Genesys Logic GL975x support
- sdhci-tegra: Recover loss in throughput for DMA
- sdhci-of-esdhc: Fix DMA bug"
* tag 'mmc-v5.4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc:
mmc: host: sdhci-pci: Add Genesys Logic GL975x support
mmc: tegra: Implement ->set_dma_mask()
mmc: sdhci: Let drivers define their DMA mask
mmc: sdhci-of-esdhc: set DMA snooping based on DMA coherence
mmc: sdhci: improve ADMA error reporting
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Move the static keyword to the front of declaration of
csky_pmu_of_device_ids, and resolve the following compiler
warning that can be seen when building with warnings
enabled (W=1):
arch/csky/kernel/perf_event.c:1340:1: warning:
‘static’ is not at beginning of declaration [-Wold-style-declaration]
Signed-off-by: Krzysztof Wilczynski <kw@linux.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
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Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
Pull Documentation/process update from Greg KH:
"Here are two small Documentation/process/embargoed-hardware-issues.rst
file updates that missed my previous char/misc pull request.
The first one adds an Intel representative for the process, and the
second one cleans up the text a bit more when it comes to how the
disclosure rules work, as it was a bit confusing to some companies"
* tag 'char-misc-5.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
Documentation/process: Clarify disclosure rules
Documentation/process: Volunteer as the ambassador for Intel
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git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull more vfs updates from Al Viro:
"A couple of misc patches"
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
afs dynroot: switch to simple_dir_operations
fs/handle.c - fix up kerneldoc
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Pull more cifs updates from Steve French:
"Fixes from the recent SMB3 Test events and Storage Developer
Conference (held the last two weeks).
Here are nine smb3 patches including an important patch for debugging
traces with wireshark, with three patches marked for stable.
Additional fixes from last week to better handle some newly discovered
reparse points, and a fix the create/mkdir path for setting the mode
more atomically (in SMB3 Create security descriptor context), and one
for path name processing are still being tested so are not included
here"
* tag '5.4-rc-smb3-fixes' of git://git.samba.org/sfrench/cifs-2.6:
CIFS: Fix oplock handling for SMB 2.1+ protocols
smb3: missing ACL related flags
smb3: pass mode bits into create calls
smb3: Add missing reparse tags
CIFS: fix max ea value size
fs/cifs/sess.c: Remove set but not used variable 'capabilities'
fs/cifs/smb2pdu.c: Make SMB2_notify_init static
smb3: fix leak in "open on server" perf counter
smb3: allow decryption keys to be dumped by admin for debugging
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The csky_pmu.max_period has type u64, and BIT() can only return
32 bits unsigned long on C-SKY. The initialization for max_period
will be incorrect when count_width is bigger than 32.
Use BIT_ULL()
Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
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We need set fp zero to let backtrace know the end. The patch fixup perf
callchain panic problem, because backtrace didn't know what is the end
of fp.
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reported-by: Mao Han <han_mao@c-sky.com>
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The csky implementation of free_initrd_mem() is an open-coded version of
free_reserved_area() without poisoning.
Remove it and make csky use the generic version of free_initrd_mem().
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
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Merge active entropy generation updates.
This is admittedly partly "for discussion". We need to have a way
forward for the boot time deadlocks where user space ends up waiting for
more entropy, but no entropy is forthcoming because the system is
entirely idle just waiting for something to happen.
While this was triggered by what is arguably a user space bug with
GDM/gnome-session asking for secure randomness during early boot, when
they didn't even need any such truly secure thing, the issue ends up
being that our "getrandom()" interface is prone to that kind of
confusion, because people don't think very hard about whether they want
to block for sufficient amounts of entropy.
The approach here-in is to decide to not just passively wait for entropy
to happen, but to start actively collecting it if it is missing. This
is not necessarily always possible, but if the architecture has a CPU
cycle counter, there is a fair amount of noise in the exact timings of
reasonably complex loads.
We may end up tweaking the load and the entropy estimates, but this
should be at least a reasonable starting point.
As part of this, we also revert the revert of the ext4 IO pattern
improvement that ended up triggering the reported lack of external
entropy.
* getrandom() active entropy waiting:
Revert "Revert "ext4: make __ext4_get_inode_loc plug""
random: try to actively add entropy rather than passively wait for it
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This reverts commit 72dbcf72156641fde4d8ea401e977341bfd35a05.
Instead of waiting forever for entropy that may just not happen, we now
try to actively generate entropy when required, and are thus hopefully
avoiding the problem that caused the nice ext4 IO pattern fix to be
reverted.
So revert the revert.
Cc: Ahmed S. Darwish <darwish.07@gmail.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Alexander E. Patrakov <patrakov@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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For 5.3 we had to revert a nice ext4 IO pattern improvement, because it
caused a bootup regression due to lack of entropy at bootup together
with arguably broken user space that was asking for secure random
numbers when it really didn't need to.
See commit 72dbcf721566 (Revert "ext4: make __ext4_get_inode_loc plug").
This aims to solve the issue by actively generating entropy noise using
the CPU cycle counter when waiting for the random number generator to
initialize. This only works when you have a high-frequency time stamp
counter available, but that's the case on all modern x86 CPU's, and on
most other modern CPU's too.
What we do is to generate jitter entropy from the CPU cycle counter
under a somewhat complex load: calling the scheduler while also
guaranteeing a certain amount of timing noise by also triggering a
timer.
I'm sure we can tweak this, and that people will want to look at other
alternatives, but there's been a number of papers written on jitter
entropy, and this should really be fairly conservative by crediting one
bit of entropy for every timer-induced jump in the cycle counter. Not
because the timer itself would be all that unpredictable, but because
the interaction between the timer and the loop is going to be.
Even if (and perhaps particularly if) the timer actually happens on
another CPU, the cacheline interaction between the loop that reads the
cycle counter and the timer itself firing is going to add perturbations
to the cycle counter values that get mixed into the entropy pool.
As Thomas pointed out, with a modern out-of-order CPU, even quite simple
loops show a fair amount of hard-to-predict timing variability even in
the absense of external interrupts. But this tries to take that further
by actually having a fairly complex interaction.
This is not going to solve the entropy issue for architectures that have
no CPU cycle counter, but it's not clear how (and if) that is solvable,
and the hardware in question is largely starting to be irrelevant. And
by doing this we can at least avoid some of the even more contentious
approaches (like making the entropy waiting time out in order to avoid
the possibly unbounded waiting).
Cc: Ahmed Darwish <darwish.07@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Nicholas Mc Guire <hofrat@opentech.at>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Alexander E. Patrakov <patrakov@gmail.com>
Cc: Lennart Poettering <mzxreary@0pointer.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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