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2e0733bc5a
linux/drivers/spi
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Lukas Wunner 2e0733bc5a
spi: bcm2835: Speed up FIFO access if fill level is known 
The RX and TX FIFO of the BCM2835 SPI master each accommodate 64 bytes
(16 32-bit dwords).  The CS register provides hints on their fill level:

   "Bit 19  RXR - RX FIFO needs Reading ([¾] full)
    0 = RX FIFO is less than [¾] full (or not active TA = 0).
    1 = RX FIFO is [¾] or more full. Cleared by reading sufficient
        data from the RX FIFO or setting TA to 0."

   "Bit 16  DONE - Transfer Done
    0 = Transfer is in progress (or not active TA = 0).
    1 = Transfer is complete. Cleared by writing more data to the
        TX FIFO or setting TA to 0."

   "If DONE is set [...], write up to 16 [dwords] to SPI_FIFO. [...]
    If RXR is set read 12 [dwords] data from SPI_FIFO."

   [Source: Pages 153, 154 and 158 of
    https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
    Note: The spec is missing the "¾" character, presumably due to
    copy-pasting from a different charset.  It also incorrectly
    refers to 16 and 12 "bytes" instead of 32-bit dwords.]

In short, the RXR bit indicates that 48 bytes can be read and the DONE
bit indicates 64 bytes can be written.  Leverage this knowledge to read
or write bytes blindly to the FIFO, without polling whether data can be
read or free space is available to write.  Moreover, when a transfer is
starting, the TX FIFO is known to be empty, likewise allowing a blind
write of 64 bytes.

This cuts the number of bus accesses in half if the fill level is known.
Also, the (posted) write accesses can be pipelined on the AXI bus since
they are no longer interleaved with (non-posted) reads.

bcm2835_spi_transfer_one_poll() switches to interrupt mode when a time
limit is exceeded by calling bcm2835_spi_transfer_one_irq().  The TX
FIFO may contain data in this case, but is known to be empty when the
function is called from bcm2835_spi_transfer_one().  Hence only blindly
fill the TX FIFO in the latter case but not the former.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Eric Anholt <eric@anholt.net>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Martin Sperl <kernel@martin.sperl.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
2018-12-04 16:51:41 +00:00
..
internals.h spi: Add an helper to flush the message queue 2018-04-23 15:48:18 +01:00
Kconfig spi: npcm: add NPCM PSPI controller driver 2018-11-13 12:01:22 -08:00
Makefile spi: npcm: add NPCM PSPI controller driver 2018-11-13 12:01:22 -08:00
spi-altera.c spi: altera: Consolidate TX/RX data register access 2017-08-16 11:53:31 +01:00
spi-armada-3700.c Merge remote-tracking branches 'spi/topic/a3700', 'spi/topic/atmel', 'spi/topic/bcm53xx', 'spi/topic/davinci' and 'spi/topic/dw' into spi-next 2018-01-26 17:57:24 +00:00
spi-at91-usart.c spi: fix spi-at91-usart.c build errors when PINCTRL is not set 2018-12-03 11:57:14 +00:00
spi-ath79.c spi: add flags parameter to txrx_word function pointers 2018-08-01 14:50:24 +01:00
spi-atmel.c spi: Do not print a message if spi_controller_{suspend,resume}() fails 2018-09-05 12:38:27 +01:00
spi-au1550.c
spi-axi-spi-engine.c spi: spi-axi: fix potential use-after-free after deregistration 2017-10-31 11:15:10 +00:00
spi-bcm63xx-hsspi.c spi/bcm63xx-hsspi: keep pll clk enabled 2018-09-18 09:16:34 -07:00
spi-bcm63xx.c spi/bcm63xx: fix error return code in bcm63xx_spi_probe() 2017-08-08 11:36:35 +01:00
spi-bcm2835.c spi: bcm2835: Speed up FIFO access if fill level is known 2018-12-04 16:51:41 +00:00
spi-bcm2835aux.c spi: bcm2835: make license text and module license match 2018-11-14 14:18:18 -08:00
spi-bcm-qspi.c spi: bcm-qspi: switch back to reading flash using smaller chunks 2018-10-11 15:00:34 +01:00
spi-bcm-qspi.h
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 spi: spi-gpio: add SPI_3WIRE support 2018-08-01 14:50:28 +01:00
spi-brcmstb-qspi.c
spi-butterfly.c spi: add flags parameter to txrx_word function pointers 2018-08-01 14:50:24 +01:00
spi-cadence.c spi: cadence: Fix missing clk_disable_unprepare() on error in cnds_runtime_resume() 2018-07-11 15:34:53 +01:00
spi-cavium-octeon.c
spi-cavium-thunderx.c
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-coldfire-qspi.c
spi-davinci.c spi: spi-davinci: Don't error when SPI_CS_WORD and cs_gpio 2018-09-18 10:40:34 -07:00
spi-dln2.c
spi-dw-mid.c spi: dw: Convert to generalized SPI controller API 2018-02-12 12:04:16 +00:00
spi-dw-mmio.c dw: spi: add support for Amazon's Alpine spi controller 2018-10-11 15:11:04 +01:00
spi-dw-pci.c
spi-dw.c dw: spi: add support for Amazon's Alpine spi controller 2018-10-11 15:11:04 +01:00
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-ep93xx.c spi: spi-ep93xx: Use dma_data_direction for ep93xx_spi_dma_{finish,prepare} 2018-10-09 00:11:28 +01:00
spi-falcon.c spi: spi-falcon: drop check of boot select 2017-09-01 11:33:22 +01:00
spi-fsl-cpm.c
spi-fsl-cpm.h
spi-fsl-dspi.c spi: spi-fsl-dspi: use IRQF_SHARED mode to request IRQ 2018-11-05 11:53:28 +00:00
spi-fsl-espi.c spi: Do not print a message if spi_controller_{suspend,resume}() fails 2018-09-05 12:38:27 +01:00
spi-fsl-lib.c
spi-fsl-lib.h
spi-fsl-lpspi.c spi: fsl-lpspi: Prevent FIFO under/overrun by default 2018-10-10 12:41:36 +01:00
spi-fsl-spi.c Merge remote-tracking branches 'spi/topic/devprop', 'spi/topic/fsl', 'spi/topic/fsl-dspi', 'spi/topic/imx' and 'spi/topic/lantiq' into spi-next 2017-04-26 15:58:04 +01:00
spi-fsl-spi.h
spi-geni-qcom.c spi: spi-geni-qcom: Simplify probe function 2018-11-05 11:53:52 +00:00
spi-gpio.c Merge branch 'spi-4.20' into spi-next 2018-10-21 17:00:14 +01:00
spi-img-spfi.c spi: img-spfi: Set device select bits for SPFI port state 2018-07-30 16:31:54 +01:00
spi-imx.c spi: imx: use PIO mode if size is small 2018-10-12 18:54:02 +02:00
spi-iproc-qspi.c
spi-jcore.c spi: jcore: disable ref_clk after getting its rate 2018-03-18 17:57:42 -07:00
spi-lantiq-ssc.c Merge remote-tracking branches 'spi/topic/devprop', 'spi/topic/fsl', 'spi/topic/fsl-dspi', 'spi/topic/imx' and 'spi/topic/lantiq' into spi-next 2017-04-26 15:58:04 +01:00
spi-lm70llp.c spi: add flags parameter to txrx_word function pointers 2018-08-01 14:50:24 +01:00
spi-loopback-test.c spi: loopback-test: implement testing with no CS 2017-07-26 13:08:56 +01:00
spi-lp8841-rtc.c
spi-mem.c spi: spi-mem: add support for octal mode I/O data transfer 2018-12-03 17:20:14 +00:00
spi-meson-spicc.c spi: meson-spicc: Fix error handling in meson_spicc_probe() 2018-05-02 05:59:21 +09:00
spi-meson-spifc.c
spi-mpc52xx-psc.c
spi-mpc52xx.c spi: mpc52xx: Use gpio_is_valid() 2018-04-27 12:05:39 +01:00
spi-mpc512x-psc.c
spi-mt65xx.c spi: mediatek: add spi support for mt7629 IC 2018-11-27 14:17:20 +00:00
spi-mxic.c spi: Add MXIC controller driver 2018-11-05 11:55:06 +00:00
spi-mxs.c spi: mxs: Switch to SPDX identifier 2018-05-03 10:27:43 +09:00
spi-npcm-pspi.c spi: npcm: Fix uninitialized variable warning 2018-11-27 14:07:08 +00:00
spi-nuc900.c
spi-oc-tiny.c treewide: devm_kzalloc() -> devm_kcalloc() 2018-06-12 16:19:22 -07:00
spi-omap2-mcspi.c spi: omap2-mcspi: Add missing suspend and resume calls 2018-11-15 16:20:43 -08:00
spi-omap-100k.c
spi-omap-uwire.c
spi-orion.c spi: orion: cosmetics - alias long direct_access variables 2018-09-03 15:14:18 +01:00
spi-pic32-sqi.c spi: pic32-sqi: don't pass GFP_DMA32 to dma_alloc_coherent 2018-10-17 11:11:32 +01:00
spi-pic32.c spi: pic32: Use proper enum in dmaengine_prep_slave_rg 2018-09-20 18:11:22 -07:00
spi-pl022.c spi: pl022: Handle cs_change for last transfer 2018-11-13 10:05:49 -08:00
spi-ppc4xx.c
spi-pxa2xx-dma.c spi: pxa2xx: Use core message processing loop 2018-04-17 17:11:30 +01:00
spi-pxa2xx-pci.c spi: pca2xx-pci: Allow MSI 2017-01-23 18:09:37 +00:00
spi-pxa2xx.c spi: pxa2xx: Fix '"CONFIG_OF" is not defined' warning 2018-11-16 19:06:24 -08:00
spi-pxa2xx.h spi: pxa2xx: Add ready signal 2018-11-13 10:02:09 -08:00
spi-qcom-qspi.c spi: Introduce new driver for Qualcomm QuadSPI controller 2018-10-11 15:11:09 +01:00
spi-qup.c spi: qup: fix 64-bit build warning 2017-08-10 15:50:23 +01:00
spi-rb4xx.c spi: rb4xx: Use SPI_BPW_MASK to set bits_per_word_mask 2018-10-10 12:48:06 +01:00
spi-rockchip.c spi: rockchip: support lsb-first mode 2018-11-05 11:42:43 +00:00
spi-rspi.c spi: spi-rspi: simplify getting .driver_data 2018-11-05 11:54:50 +00:00
spi-s3c24xx-fiq.h
spi-s3c24xx-fiq.S
spi-s3c24xx.c
spi-s3c64xx.c spi: spi-s3c64xx: Fix system resume support 2018-05-17 13:27:08 +09:00
spi-sc18is602.c spi: sc18is602: Add OF device ID table 2017-02-22 10:50:09 -08:00
spi-sh-hspi.c spi: use SPDX identifier for Renesas drivers 2018-08-28 20:32:00 +01:00
spi-sh-msiof.c spi: spi-sh-msiof: simplify getting .driver_data 2018-11-05 11:54:20 +00:00
spi-sh-sci.c spi: add flags parameter to txrx_word function pointers 2018-08-01 14:50:24 +01:00
spi-sh.c spi: use SPDX identifier for Renesas drivers 2018-08-28 20:32:00 +01:00
spi-sirf.c spi: sirf: account for const type of of_device_id.data 2018-01-03 11:38:46 +00:00
spi-slave-mt27xx.c spi: mediatek: add spi slave for Mediatek MT2712 2018-09-28 14:29:14 +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: Change to use devm_hwspin_lock_request_specific() 2018-06-26 13:52:27 -07:00
spi-sprd.c spi: sprd: don't mark remove function as __exit 2018-09-27 23:26:43 +01:00
spi-st-ssc4.c spi: st-ssc4: whitespace cleanup 2017-05-26 12:41:07 +01:00
spi-stm32-qspi.c spi: spi-mem: add stm32 qspi controller 2018-10-19 13:32:56 +01:00
spi-stm32.c spi: stm32: Fix error handling in stm32_spi_probe() 2018-04-17 11:46:23 +01:00
spi-sun4i.c spi: sun4i: disable clocks in the remove function 2017-12-07 11:59:15 +00:00
spi-sun6i.c spi: sun6i: disable/unprepare clocks on remove 2017-12-07 17:45:17 +00:00
spi-tegra20-sflash.c spi: tegra20-sflash: explicitly request exclusive reset control 2017-07-19 17:06:31 +01:00
spi-tegra20-slink.c spi: tegra20-slink: explicitly enable/disable clock 2018-09-03 12:23:41 +01:00
spi-tegra114.c spi: tegra114: correct register name in definition 2017-10-09 10:16:38 +01:00
spi-test.h spi: loopback-test: add elapsed time check 2017-03-17 21:54:08 +00:00
spi-ti-qspi.c spi: ti-qspi: Make sure res_mmap != NULL before dereferencing it 2018-05-17 13:36:00 +09:00
spi-tle62x0.c
spi-topcliff-pch.c spi/topcliff-pch: Delete an error message for a failed memory allocation in pch_spi_set_tx() 2017-01-17 18:38:02 +00:00
spi-txx9.c
spi-uniphier.c spi: uniphier: remove unnecessary include headers 2018-08-02 11:08:06 +01:00
spi-xcomm.c
spi-xilinx.c spi: xilinx: Add support for xlnx,axi-quad-spi-1.00.a 2017-11-27 16:31:20 +00:00
spi-xlp.c spi: xlp: fix error return code in xlp_spi_probe() 2017-08-08 11:36:07 +01:00
spi-xtensa-xtfpga.c spi: add flags parameter to txrx_word function pointers 2018-08-01 14:50:24 +01:00
spi-zynqmp-gqspi.c spi: spi-zynqmp-gqspi: simplify getting .driver_data 2018-11-05 11:54:35 +00:00
spi.c spi: add support for octal mode I/O data transfer 2018-12-03 17:14:53 +00:00
spidev.c spi: spidev: Fix OF tree warning logic 2018-10-10 13:46:54 +01:00