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linux/drivers/spi
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Vladimir Oltean 79591b7db2
spi: Add a PTP system timestamp to the transfer structure 
SPI is one of the interfaces used to access devices which have a POSIX
clock driver (real time clocks, 1588 timers etc). The fact that the SPI
bus is slow is not what the main problem is, but rather the fact that
drivers don't take a constant amount of time in transferring data over
SPI. When there is a high delay in the readout of time, there will be
uncertainty in the value that has been read out of the peripheral.
When that delay is constant, the uncertainty can at least be
approximated with a certain accuracy which is fine more often than not.

Timing jitter occurs all over in the kernel code, and is mainly caused
by having to let go of the CPU for various reasons such as preemption,
servicing interrupts, going to sleep, etc. Another major reason is CPU
dynamic frequency scaling.

It turns out that the problem of retrieving time from a SPI peripheral
with high accuracy can be solved by the use of "PTP system
timestamping" - a mechanism to correlate the time when the device has
snapshotted its internal time counter with the Linux system time at that
same moment. This is sufficient for having a precise time measurement -
it is not necessary for the whole SPI transfer to be transmitted "as
fast as possible", or "as low-jitter as possible". The system has to be
low-jitter for a very short amount of time to be effective.

This patch introduces a PTP system timestamping mechanism in struct
spi_transfer. This is to be used by SPI device drivers when they need to
know the exact time at which the underlying device's time was
snapshotted. More often than not, SPI peripherals have a very exact
timing for when their SPI-to-interconnect bridge issues a transaction
for snapshotting and reading the time register, and that will be
dependent on when the SPI-to-interconnect bridge figures out that this
is what it should do, aka as soon as it sees byte N of the SPI transfer.
Since spi_device drivers are the ones who'd know best how the peripheral
behaves in this regard, expose a mechanism in spi_transfer which allows
them to specify which word (or word range) from the transfer should be
timestamped.

Add a default implementation of the PTP system timestamping in the SPI
core. This is not going to be satisfactory performance-wise, but should
at least increase the likelihood that SPI device drivers will use PTP
system timestamping in the future.
There are 3 entry points from the core towards the SPI controller
drivers:

- transfer_one: The driver is passed individual spi_transfers to
  execute. This is the easiest to timestamp.

- transfer_one_message: The core passes the driver an entire spi_message
  (a potential batch of spi_transfers). The core puts the same pre and
  post timestamp to all transfers within a message. This is not ideal,
  but nothing better can be done by default anyway, since the core has
  no insight into how the driver batches the transfers.

- transfer: Like transfer_one_message, but for unqueued drivers (i.e.
  the driver implements its own queue scheduling).

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20190905010114.26718-3-olteanv@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>
 		2019-10-08 17:38:15 +01:00
..
Kconfig It's a somewhat calmer cycle for docs this time, as the churn of the mass 2019-09-17 16:22:26 -07:00
Makefile ARM: SoC driver updates for v5.4 2019-09-16 15:52:38 -07:00
atmel-quadspi.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
internals.h spi: Add an helper to flush the message queue 2018-04-23 15:48:18 +01:00
spi-altera.c spi: altera: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:14:50 +01:00
spi-armada-3700.c spi: a3700: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:15:09 +01:00
spi-at91-usart.c spi: at91-usart: add DMA support 2019-05-08 17:45:26 +09:00
spi-ath79.c spi: ath79: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:15:29 +01:00
spi-atmel.c spi: atmel: add tracing to custom .transfer_one_message callback 2019-08-02 12:16:02 +01:00
spi-au1550.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-axi-spi-engine.c spi: spi-axi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:15:49 +01:00
spi-bcm-qspi.c Merge branch 'spi-5.3' into spi-linus 2019-09-15 10:32:04 +01:00
spi-bcm-qspi.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 459 2019-06-19 17:09:09 +02:00
spi-bcm63xx-hsspi.c spi: bcm63xx-hsspi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:16:47 +01:00
spi-bcm63xx.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-bcm2835.c Merge branch 'spi-5.4' into spi-next 2019-09-15 10:32:06 +01:00
spi-bcm2835aux.c spi: bcm2835aux: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:16:08 +01:00
spi-bitbang-txrx.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
spi-bitbang.c Linux 5.2-rc4 2019-06-10 18:52:53 +01:00
spi-brcmstb-qspi.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 459 2019-06-19 17:09:09 +02:00
spi-butterfly.c spi: docs: convert to ReST and add it to the kABI bookset 2019-07-31 14:13:13 -06:00
spi-cadence.c spi: cadence: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:17:07 +01:00
spi-cavium-octeon.c spi: octeon: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:17:27 +01:00
spi-cavium-thunderx.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
spi-cavium.c
…
spi-cavium.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
spi-clps711x.c spi: clps711x: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:17:36 +01:00
spi-coldfire-qspi.c spi: coldfire-qspi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:17:56 +01:00
spi-davinci.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-dln2.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 372 2019-06-05 17:37:10 +02:00
spi-dw-mid.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 288 2019-06-05 17:36:37 +02:00
spi-dw-mmio.c spi: dw-mmio: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:18:05 +01:00
spi-dw-pci.c Merge branch 'spi-5.4' into spi-next 2019-09-15 10:32:06 +01:00
spi-dw.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 288 2019-06-05 17:36:37 +02:00
spi-dw.h dw: spi: add support for Amazon's Alpine spi controller 2018-10-11 15:11:04 +01:00
spi-efm32.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-ep93xx.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-falcon.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-fsl-cpm.c spi: fsl-spi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:24:26 +01:00
spi-fsl-cpm.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
spi-fsl-dspi.c spi: spi-fsl-dspi: Fix race condition in TCFQ/EOQ interrupt 2019-09-03 12:40:05 +01:00
spi-fsl-espi.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
spi-fsl-lib.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
spi-fsl-lib.h spi: fsl: Convert to use CS GPIO descriptors 2019-08-28 14:10:41 +01:00
spi-fsl-lpspi.c spi: fsl-lpspi: Clean up fsl_lpspi_probe 2019-04-08 14:08:53 +07:00
spi-fsl-qspi.c Merge branch 'spi-5.3' into spi-5.4 2019-08-23 12:00:22 +01:00
spi-fsl-spi.c spi: fsl: Convert to use CS GPIO descriptors 2019-08-28 14:10:41 +01:00
spi-fsl-spi.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
spi-geni-qcom.c spi: spi-geni-qcom: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:18:25 +01:00
spi-gpio.c spi-gpio: Use PTR_ERR_OR_ZERO() in spi_gpio_request() 2019-09-09 11:05:39 +01:00
spi-img-spfi.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 422 2019-06-05 17:37:15 +02:00
spi-imx.c Merge branch 'spi-5.1' into spi-5.2 for stm32 2019-03-15 17:06:34 +00:00
spi-iproc-qspi.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
spi-jcore.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
spi-lantiq-ssc.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-lm70llp.c spi: docs: convert to ReST and add it to the kABI bookset 2019-07-31 14:13:13 -06:00
spi-loopback-test.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-lp8841-rtc.c spi: lp-8841: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:18:35 +01:00
spi-mem.c spi-mem: fix kernel-doc for spi_mem_dirmap_{read|write}() 2019-04-08 14:06:51 +07:00
spi-meson-spicc.c spi: meson-spicc: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:18:55 +01:00
spi-meson-spifc.c spi: spi-meson-spifc: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:19:14 +01:00
spi-mpc52xx-psc.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
spi-mpc52xx.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 428 2019-06-05 17:37:16 +02:00
spi-mpc512x-psc.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
spi-mt65xx.c spi: mediatek: support large PA 2019-09-13 10:41:10 +01:00
spi-mt7621.c spi: mt7621: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:19:34 +01:00
spi-mxic.c spi: mxic: simplify getting .driver_data 2019-03-20 17:20:29 +00:00
spi-mxs.c spi: mxs: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:19:54 +01:00
spi-npcm-fiu.c spi: npcm-fiu: remove set but not used variable 'retlen' 2019-09-05 18:19:45 +01:00
spi-npcm-pspi.c spi: npcm: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:20:03 +01:00
spi-nxp-fspi.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-oc-tiny.c spi: oc-tiny: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:20:33 +01:00
spi-omap-100k.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-omap-uwire.c
…
spi-omap2-mcspi.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-orion.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-pic32-sqi.c spi: pic32-sqi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:20:52 +01:00
spi-pic32.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-pl022.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-ppc4xx.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-pxa2xx-dma.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-pxa2xx-pci.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
spi-pxa2xx.c spi: pxa2xx: Add support for Intel Tiger Lake 2019-08-02 12:14:23 +01:00
spi-pxa2xx.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-qcom-qspi.c spi: spi-qcom-qspi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:21:12 +01:00
spi-qup.c Merge branch 'spi-5.3' into spi-next 2019-07-04 17:35:07 +01:00
spi-rb4xx.c spi: rb4xx: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:21:21 +01:00
spi-rockchip.c Linux 5.2-rc4 2019-06-10 18:52:53 +01:00
spi-rspi.c spi: rspi: Fix handling of QSPI code when transmit and receive 2019-05-02 10:38:44 +09:00
spi-s3c24xx-fiq.S treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-s3c24xx-fiq.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-s3c24xx.c spi: s3c24xx: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:21:31 +01:00
spi-s3c64xx.c spi: spi-s3c64xx: Fix system resume support 2018-05-17 13:27:08 +09:00
spi-sc18is602.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-sh-hspi.c spi: sh-hspi: Replace spi_master by spi_controller 2019-02-08 13:04:19 +00:00
spi-sh-msiof.c spi: sh-msiof: Use devm_platform_ioremap_resource() helper 2019-08-07 14:24:47 +01:00
spi-sh-sci.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-sh.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-sifive.c spi: sifive: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:21:41 +01:00
spi-sirf.c spi: sirf: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:22:00 +01:00
spi-slave-mt27xx.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-slave-system-control.c spi: slave: Fix missing break in switch 2018-10-03 16:23:10 +01:00
spi-slave-time.c spi: slave: Add SPI slave handler reporting uptime at previous message 2017-05-26 13:12:04 +01:00
spi-sprd-adi.c spi: sprd: adi: Change hwlock to be optional 2019-07-26 12:24:47 +01:00
spi-sprd.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-st-ssc4.c spi: st-ssc4: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:22:10 +01:00
spi-stm32-qspi.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-stm32.c spi: stm32: return the get_irq error 2019-05-02 10:38:41 +09:00
spi-sun4i.c spi: sun4i: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:22:29 +01:00
spi-sun6i.c spi: sun6i: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:22:49 +01:00
spi-synquacer.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-tegra20-sflash.c spi: tegra: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:22:58 +01:00
spi-tegra20-slink.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 201 2019-05-30 11:29:52 -07:00
spi-tegra114.c Linux 5.2-rc4 2019-06-10 18:52:53 +01:00
spi-test.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
spi-ti-qspi.c spi: Remove dev_err() usage after platform_get_irq() 2019-08-02 12:15:43 +01:00
spi-tle62x0.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-topcliff-pch.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 285 2019-06-05 17:36:37 +02:00
spi-txx9.c spi: spi-txx9: Add missing clock (un)prepare calls for CCF 2016-08-18 19:10:39 +01:00
spi-uniphier.c Merge branch 'spi-5.4' into spi-next 2019-09-15 10:32:06 +01:00
spi-xcomm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 149 2019-05-30 11:25:18 -07:00
spi-xilinx.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-xlp.c spi: xlp: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:23:28 +01:00
spi-xtensa-xtfpga.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
spi-zynq-qspi.c spi: zynq-qspi: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:24:07 +01:00
spi-zynqmp-gqspi.c spi: zynqmp: use devm_platform_ioremap_resource() to simplify code 2019-09-04 17:23:48 +01:00
spi.c spi: Add a PTP system timestamp to the transfer structure 2019-10-08 17:38:15 +01:00
spidev.c Linux 5.2-rc4 2019-06-10 18:52:53 +01:00