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Jan Kundrát 2258761213 serial: max310x: Reduce RX work starvation 
Prior to this patch, the code would happily trigger TX on some ports
before having a chance of reading the RX buffer from the rest of them.
When no flow control was used, this led to RX buffer overruns and
therefore lost data under certain circumstances.

I was able to reproduce this with MAX14830 (that's a quad channel one)
and a simple daisy-chain of RX and TX ports on the eval board:

- TX0 -> RX1
- TX1 -> RX2
- TX2 -> RX3
- TX3 -> RX0

I was testing this by transferring 2MB of data at 115200 baud via each
port. I used a Solidrun Clearfog Base (Armada 388) which was talking to
the UART over an SPI bus clocked at 26MHz (the chip's maximum). Without
this patch, I would always get a "Possible RX FIFO overrun" in dmesg,
and fewer-than-expected amount of bytes received over ttyMAX0. Results
on ttyMAX{1,2,3} tended to be correct all the time, even without the
previous patches in this series and with PIO SPI transfers ("indirect
mode" as the Marvell datasheet calls it), so I assume that heavy
congestion is needed in order to reproduce this.

A drawback of this patch is that the throughput gets reduced "a bit".
Previously, a 115200 baud resulted in about 11.2kBps throughput as
reported by a simple `pv`. With this patch, the throughput of four
parallel streams is roughly 7kBps each, and 9kBps for three streams.
There is no slowdown for one or two parallel streams.

Situation is worse if bytes are being read one-by-one (such as if the
userspace wants to perform parity/framing/break checking) and therefore
without the batched reads.

With just this patch and no other modifications on top of 4.14, I was
only getting roughly 3.6kBps with four parallel streams. The
single-stream performance was the same, and I was seeing about 7.2kBps
with two parallel streams. `perf top` said that a substantial amount of
time was spent in `finish_task_switch`, `_raw_spin_unlock_irqrestore`
and `__timer_delay`.

Signed-off-by: Jan Kundrát <jan.kundrat@cesnet.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2017-12-19 09:59:02 +01:00
..
accessibility License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
acpi ACPI / CPPC: Fix KASAN global out of bounds warning 2017-12-05 23:25:49 +01:00
amba A couple of dma-mapping updates: 2017-11-14 16:54:12 -08:00
android ANDROID: binder: fix transaction leak. 2017-11-28 16:54:45 +01:00
ata Merge branch 'for-4.15' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata 2017-11-15 14:11:41 -08:00
atm Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-11-29 13:10:25 -08:00
auxdisplay auxdisplay: img-ascii-lcd: Only build on archs that have IOMEM 2017-11-27 12:36:45 -08:00
base Power management fix for v4.15-rc3 2017-12-08 09:58:10 -08:00
bcma Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2017-11-15 11:56:19 -08:00
block Merge branch 'for-linus' of git://git.kernel.dk/linux-block 2017-12-01 08:05:45 -05:00
bluetooth Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-11-04 09:26:51 +09:00
bus bus: arm-ccn: fix module unloading Error: Removing state 147 which has instances left. 2017-12-04 17:15:20 +00:00
cdrom Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
char Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-26 14:11:54 -08:00
clk We have two changes to the core framework this time around. The first being a 2017-11-17 20:04:24 -08:00
clocksource - final batch of "non trivial" timer conversions (multi-tree dependencies, 2017-11-23 16:29:05 +01:00
connector
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cpufreq cpufreq: mediatek: add missing MODULE_DESCRIPTION/AUTHOR/LICENSE 2017-11-22 00:00:14 +01:00
cpuidle powerpc updates for 4.15 2017-11-16 12:47:46 -08:00
crypto powerpc updates for 4.15 2017-11-16 12:47:46 -08:00
dax device-dax: implement ->split() to catch invalid munmap attempts 2017-11-29 18:40:42 -08:00
dca
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devfreq Merge branches 'pm-devfreq' and 'pm-tools' 2017-11-13 01:41:39 +01:00
dio License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dma dmaengine updates for 4.15-rc1 2017-11-14 16:49:31 -08:00
dma-buf Tracing updates for 4.15: 2017-11-17 14:58:01 -08:00
edac Modules updates for v4.15 2017-11-15 13:46:33 -08:00
eisa License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
extcon USB/PHY patches for 4.15-rc1 2017-11-13 21:14:07 -08:00
firewire Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
firmware ARM: SoC fixes for 4.15-rc 2017-12-10 08:26:59 -08:00
fmc License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fpga Char/Misc patches for 4.15-rc1 2017-11-16 09:10:59 -08:00
fsi
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gpio gpio: pca953x: fix vendor prefix for PCA9654 2017-12-02 22:41:43 +01:00
gpu Merge tag 'drm-misc-fixes-2017-12-07' of git://anongit.freedesktop.org/drm/drm-misc into drm-fixes 2017-12-08 08:17:53 +10:00
hid treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
hsi HSI changes for the v4.15 series 2017-11-15 13:35:43 -08:00
hv Drivers: hv: vmbus: Fix a rescind issue 2017-11-28 16:56:26 +01:00
hwmon hwmon: (jc42) optionally try to disable the SMBUS timeout 2017-11-30 13:12:44 -08:00
hwspinlock hwspinlock update for v4.15 2017-11-17 20:16:20 -08:00
hwtracing Char/Misc patches for 4.15-rc1 2017-11-16 09:10:59 -08:00
i2c i2c: i2c-boardinfo: fix memory leaks on devinfo 2017-11-27 19:14:29 +01:00
ide Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/ide 2017-11-19 08:04:41 -10:00
idle Merge branch 'pm-cpuidle' 2017-11-13 01:34:14 +01:00
iio iio: health: max30102: Temperature should be in milli Celsius 2017-12-02 11:15:14 +00:00
infiniband Here is the first rc pull request for RDMA. This includes an important core 2017-12-05 10:10:15 -08:00
input treewide: Remove TIMER_FUNC_TYPE and TIMER_DATA_TYPE casts 2017-11-21 16:35:54 -08:00
iommu IOMMU fixes for Linux v4.15-rc3 2017-12-06 10:53:02 -08:00
ipack
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irqchip Merge branch 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-26 14:39:20 -08:00
isdn treewide: setup_timer() -> timer_setup() (2 field) 2017-11-21 15:57:09 -08:00
leds LED updates for 4.15rc1 2017-11-14 18:09:31 -08:00
lightnvm lightnvm: Convert timers to use timer_setup() 2017-11-21 15:46:44 -08:00
macintosh Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
mailbox Change to POLL api and fixes for FlexRM and OMAP driver 2017-11-15 13:39:18 -08:00
mcb License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
md md/raid1/10: add missed blk plug 2017-12-01 12:19:48 -08:00
media media fixes for v4.15-rc3 2017-12-08 13:18:47 -08:00
memory ARM: SoC driver updates for v4.15 2017-11-16 16:05:01 -08:00
memstick treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
message Modules updates for v4.15 2017-11-15 13:46:33 -08:00
mfd treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
misc Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2017-12-03 10:48:24 -05:00
mmc MMC core: 2017-12-01 08:14:22 -05:00
mtd Rename superblock flags (MS_xyz -> SB_xyz) 2017-11-27 13:05:09 -08:00
mux
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net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-08 13:32:44 -08:00
nfc treewide: setup_timer() -> timer_setup() (2 field) 2017-11-21 15:57:09 -08:00
ntb treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
nubus m68k updates for 4.15 2017-11-13 12:10:24 -08:00
nvdimm libnvdimm for 4.15 2017-11-17 09:51:57 -08:00
nvme nvme-pci: fix NULL pointer dereference in nvme_free_host_mem() 2017-11-28 08:49:26 -08:00
nvmem nvmem: meson-mx-efuse: fix reading from an offset other than 0 2017-12-19 09:56:03 +01:00
of of: overlay: Make node skipping in init_overlay_changeset() clearer 2017-12-08 09:32:18 -06:00
opp
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oprofile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
parisc License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
parport Char/Misc patches for 4.15-rc1 2017-11-16 09:10:59 -08:00
pci Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-26 14:11:54 -08:00
pcmcia drivers/pcmcia/sa1111_badge4.c: avoid unused function warning 2017-11-17 16:10:04 -08:00
perf arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
phy USB/PHY patches for 4.15-rc1 2017-11-13 21:14:07 -08:00
pinctrl pinctrl: sunxi: Disable strict mode for H5 driver 2017-11-30 16:50:43 +01:00
platform Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-25 08:37:16 -10:00
pnp License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
power power supply and reset changes for the v4.15 series 2017-11-15 13:37:15 -08:00
powercap
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pps treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
ps3
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ptp xen: features and fixes for v4.15-rc1 2017-11-16 13:06:27 -08:00
pwm pwm: Changes for v4.15-rc1 2017-11-22 21:09:18 -10:00
rapidio Merge branch 'akpm' (patches from Andrew) 2017-11-17 16:56:17 -08:00
ras Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 17:56:58 -08:00
regulator - New Drivers 2017-11-16 09:15:57 -08:00
remoteproc remoteproc updates for v4.15 2017-11-17 20:14:10 -08:00
reset ARM: SoC driver updates for v4.15 2017-11-16 16:05:01 -08:00
rpmsg rpmsg updates for v4.15 2017-11-17 20:12:08 -08:00
rtc Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-25 08:37:16 -10:00
s390 s390: add a few more SPDX identifiers 2017-12-05 07:51:09 +01:00
sbus Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc 2017-11-17 20:21:44 -08:00
scsi SCSI fixes on 20171205 2017-12-05 10:31:32 -08:00
sfi
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sh A couple of dma-mapping updates: 2017-11-14 16:54:12 -08:00
sn
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soc meson-gx-socinfo: Fix package id parsing 2017-11-30 15:29:44 -08:00
spi Merge remote-tracking branches 'spi/topic/sh-msiof', 'spi/topic/slave', 'spi/topic/spreadtrum' and 'spi/topic/tegra114' into spi-next 2017-11-10 21:33:51 +00:00
spmi
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ssb License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
staging Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-12-08 13:32:44 -08:00
target Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-25 08:37:16 -10:00
tc
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tee optee: fix invalid of_node_put() in optee_driver_init() 2017-11-29 10:24:57 +01:00
thermal Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux 2017-11-17 14:31:27 -08:00
thunderbolt Char/Misc patches for 4.15-rc1 2017-11-16 09:10:59 -08:00
tty serial: max310x: Reduce RX work starvation 2017-12-19 09:59:02 +01:00
uio License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
usb usb: xhci: fix panic in xhci_free_virt_devices_depth_first 2017-12-01 15:24:59 +00:00
uwb treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
vfio VFIO Updates for Linux v4.15 2017-11-14 16:47:47 -08:00
vhost vhost: fix skb leak in handle_rx() 2017-12-02 21:31:03 -05:00
video fbdev changes for v4.15: 2017-11-20 21:50:24 -10:00
virt
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virtio virtio_mmio: add cleanup for virtio_mmio_remove 2017-12-07 18:30:50 +02:00
vlynq
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vme Char/Misc patches for 4.15-rc1 2017-11-16 09:10:59 -08:00
w1 Char/Misc patches for 4.15-rc1 2017-11-16 09:10:59 -08:00
watchdog treewide: setup_timer() -> timer_setup() 2017-11-21 15:57:07 -08:00
xen xen: fixes for 4.15-rc3 2017-12-08 12:53:43 -08:00
zorro License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig Merge branches 'pm-cpufreq-sched' and 'pm-opp' 2017-11-13 01:40:52 +01:00
Makefile usb: build drivers/usb/common/ when USB_SUPPORT is set 2017-11-28 15:17:49 +01:00