leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
e2540da86e
linux/drivers
History
David Lechner e2540da86e iio: adc: ti-ads7950: use SPI_CS_WORD to reduce CPU usage 
This changes how the SPI message for the triggered buffer is setup in
the TI ADS7950 A/DC driver. By using the SPI_CS_WORD flag, we can read
multiple samples in a single SPI transfer. If the SPI controller
supports DMA transfers, we can see a significant reduction in CPU usage.

For example, on an ARM9 system running at 456MHz reading just 4 channels
at 100Hz: before this change, top shows the CPU usage of the IRQ thread
of this driver to be ~7.7%. After this change, the CPU usage drops to
~3.8%.

The use of big-endian for the raw data was cargo culted from another
driver when this driver was originally written. It used an SPI word size
of 8 bits and big-endian byte ordering to effectively emulate 16 bit
words.

Now, in order to inject a CS toggle between each word, we need to use
the correct word size, otherwise we would get a CS toggle half way
through each word 16-bit. The SPI subsystem uses CPU byte ordering for
multi-byte words. So, the data we get back from the SPI is going to be
CPU endian now no matter what. Converting that to big endian will just
add overhead on little endian systems so we opt to change the raw data
format from big endian to CPU endian.

There is a small risk that this could break some lazy userspace programs
that use the raw data without checking the data format. We can address
this if/when it actually comes up.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
2018-09-22 10:09:47 +01:00
..
accessibility
acpi libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
amba
android android: binder: Rate-limit debug and userspace triggered err msgs 2018-08-08 11:05:47 +02:00
ata Merge branch 'for-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata 2018-08-24 13:20:33 -07:00
atm
auxdisplay Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
base regmap: Support non-incrementing registers 2018-08-19 18:06:59 +01:00
bcma
block Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
bluetooth Bluetooth: mediatek: pass correct size to h4_recv_buf() 2018-08-13 15:59:39 +02:00
bus ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
cdrom cdrom: Use struct scsi_sense_hdr internally 2018-08-02 15:22:39 -06:00
char RTC for 4.19 2018-08-20 16:30:27 -07:00
clk ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
clocksource RISC-V Updates for the 4.19 Merge Window 2018-08-19 09:56:38 -07:00
connector
cpufreq ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
cpuidle More power management updates for 4.19-rc1 2018-08-22 07:42:36 -07:00
crypto Merge branch 'akpm' (patches from Andrew) 2018-08-23 19:20:12 -07:00
dax libnvdimm-for-4.19_dax-memory-failure 2018-08-25 18:43:59 -07:00
dca
devfreq Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
dio
dma Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
dma-buf
edac EDAC: Add missing MEM_LRDDR4 entry in edac_mem_types[] 2018-08-17 15:13:34 +02:00
eisa
extcon
firewire firewire: use 64-bit time_t based interfaces 2018-08-17 16:20:27 -07:00
firmware fbdev changes for v4.19: 2018-08-23 15:44:58 -07:00
fmc
fpga
fsi fsi: sbefifo: Bump max command length 2018-08-08 15:44:47 +10:00
gnss
gpio - New Drivers 2018-08-20 15:38:44 -07:00
gpu Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
hid Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid 2018-08-20 15:59:01 -07:00
hsi
hv Drivers: hv: vmbus: Cleanup synic memory free path 2018-08-02 10:20:59 +02:00
hwmon ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
hwspinlock
hwtracing drivers/hwtracing/intel_th/msu.c: change return type to vm_fault_t 2018-08-23 18:48:43 -07:00
i2c i2c: don't use any __deprecated handling anymore 2018-08-24 17:26:43 +02:00
ide Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/ide 2018-08-22 07:40:33 -07:00
idle
iio iio: adc: ti-ads7950: use SPI_CS_WORD to reduce CPU usage 2018-09-22 10:09:47 +01:00
infiniband Second merge window update 2018-08-23 15:34:48 -07:00
input ARM: 32-bit SoC platform updates 2018-08-23 13:44:43 -07:00
iommu ARM: SoC: late updates 2018-08-25 14:12:36 -07:00
ipack
irqchip Merge branch 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-08-26 09:55:28 -07:00
isdn isdn: Disable IIOCDBGVAR 2018-08-16 12:26:24 -07:00
leds leds: ns2: Change unsigned to unsigned int 2018-08-06 23:03:12 +02:00
lightnvm
macintosh macintosh: therm_windtunnel: drop using attach_adapter 2018-08-24 14:42:42 +02:00
mailbox mailbox: Add support for i.MX messaging unit 2018-08-15 09:53:07 +05:30
mcb
md libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
media Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
memory ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
memstick
message
mfd Merge branch 'i2c/for-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2018-08-21 17:40:46 -07:00
misc Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
mmc Merge branch 'asoc-4.19' into asoc-next 2018-08-09 14:47:05 +01:00
mtd This pull request contains updates for both UBI and UBIFS: 2018-08-23 15:58:04 -07:00
mux mux: adgs1408: new driver for Analog Devices ADGS1408/1409 mux 2018-08-02 10:23:02 +02:00
net ARM: 32-bit SoC platform updates 2018-08-23 13:44:43 -07:00
nfc
ntb
nubus
nvdimm libnvdimm-for-4.19_dax-memory-failure 2018-08-25 18:43:59 -07:00
nvme Merge branch 'linus/master' into rdma.git for-next 2018-08-16 14:21:29 -06:00
nvmem
of Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2018-08-15 15:04:25 -07:00
opp
oprofile
parisc
parport Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
pci Merge branch 'akpm' (patches from Andrew) 2018-08-22 12:34:08 -07:00
pcmcia pcmcia: remove long deprecated pcmcia_request_exclusive_irq() function 2018-08-18 12:30:42 -07:00
perf Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
phy
pinctrl - New Drivers 2018-08-20 15:38:44 -07:00
platform platform-drivers-x86 for v4.19-1 2018-08-22 14:14:15 -07:00
pnp
power treewide: convert ISO_8859-1 text comments to utf-8 2018-08-23 18:48:43 -07:00
powercap
pps
ps3
ptp Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
pwm pwm: mediatek: Add MT7628 support 2018-08-20 11:36:07 +02:00
rapidio drivers/rapidio/devices/rio_mport_cdev.c: remove redundant pointer md 2018-08-22 10:52:51 -07:00
ras
regulator - New Drivers 2018-08-20 15:38:44 -07:00
remoteproc remoteproc/davinci: use the reset framework 2018-08-16 17:39:55 -07:00
reset ARM: SoC: late updates 2018-08-25 14:12:36 -07:00
rpmsg
rtc RTC for 4.19 2018-08-20 16:30:27 -07:00
s390 libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
sbus
scsi Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
sfi
sh sh: introduce a sh_cacheop_vaddr helper 2018-08-02 13:54:06 +02:00
siox
slimbus
sn
soc ARM: Device-tree updates 2018-08-23 14:02:22 -07:00
soundwire
spi spi: add software implementation for SPI_CS_WORD 2018-09-17 14:14:18 -07:00
spmi
ssb ssb: Remove SSB_WARN_ON, SSB_BUG_ON and SSB_DEBUG 2018-08-09 18:47:47 +03:00
staging staging:iio:ad7606: Remove incorrect kernel doc annotations 2018-09-16 12:18:36 +01:00
target Merge branch 'ida-4.19' of git://git.infradead.org/users/willy/linux-dax 2018-08-26 11:48:42 -07:00
tc
tee ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
thermal Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux 2018-08-24 13:03:51 -07:00
thunderbolt
tty powerpc fixes for 4.19 #2 2018-08-24 09:34:23 -07:00
uio Char/Misc fix for 4.19-rc1 2018-08-19 09:30:44 -07:00
usb ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
uwb
vfio powerpc updates for 4.19 2018-08-17 11:32:50 -07:00
vhost virtio, vhost: fixes, tweaks 2018-08-24 08:45:19 -07:00
video fbdev changes for v4.19: 2018-08-23 15:44:58 -07:00
virt
virtio virtio, vhost: fixes, tweaks 2018-08-24 08:45:19 -07:00
visorbus
vlynq
vme
w1 power supply and reset changes for the v4.19 series 2018-08-21 18:06:27 -07:00
watchdog include/linux/compiler*.h: make compiler-*.h mutually exclusive 2018-08-22 17:31:34 -07:00
xen xen: fixes and cleanups for 4.19-rc1, second round 2018-08-23 14:52:23 -07:00
zorro
Kconfig
Makefile Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00