dmaengine Archive on lore.kernel.org
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* [PATCH 00/10] Raspberry Pi SPI speedups
@ 2019-08-03 10:10 Lukas Wunner
  2019-08-03 10:10 ` [PATCH 01/10] dmaengine: bcm2835: Allow reusable descriptors Lukas Wunner
                   ` (15 more replies)
  0 siblings, 16 replies; 29+ messages in thread
From: Lukas Wunner @ 2019-08-03 10:10 UTC (permalink / raw)
  To: Mark Brown, Vinod Koul, Stefan Wahren, linux-spi, dmaengine,
	linux-rpi-kernel, bcm-kernel-feedback-list
  Cc: Eric Anholt, Nuno Sa, Martin Sperl, Noralf Tronnes,
	Robert Jarzmik, Florian Kauer, Florian Fainelli, Ray Jui,
	Scott Branden

So far the BCM2835 SPI driver cannot cope with TX-only and RX-only
transfers (rx_buf or tx_buf is NULL) when using DMA:  It relies on
the SPI core to convert them to full-duplex transfers by allocating
and DMA-mapping a dummy rx_buf or tx_buf.  This costs performance.

Resolve by pre-allocating reusable DMA descriptors which cyclically
clear the RX FIFO (for TX-only transfers) or zero-fill the TX FIFO
(for RX-only transfers).  Patch [07/10] provides some numbers for
the achieved latency improvement and CPU time reduction with an
SPI Ethernet controller.  SPI displays should see a similar speedup.
I've also made an effort to reduce peripheral and memory bus accesses.

The series is meant to be applied on top of broonie/for-next.
It can be applied to Linus' current tree if commit
8d8bef503658 ("spi: bcm2835: Fix 3-wire mode if DMA is enabled")
is cherry-picked from broonie's repo beforehand.

Please review and test.  Thank you.

Lukas Wunner (10):
  dmaengine: bcm2835: Allow reusable descriptors
  dmaengine: bcm2835: Allow cyclic transactions without interrupt
  spi: Guarantee cacheline alignment of driver-private data
  spi: bcm2835: Drop dma_pending flag
  spi: bcm2835: Work around DONE bit erratum
  spi: bcm2835: Cache CS register value for ->prepare_message()
  spi: bcm2835: Speed up TX-only DMA transfers by clearing RX FIFO
  dmaengine: bcm2835: Document struct bcm2835_dmadev
  dmaengine: bcm2835: Avoid accessing memory when copying zeroes
  spi: bcm2835: Speed up RX-only DMA transfers by zero-filling TX FIFO

 drivers/dma/bcm2835-dma.c |  38 +++-
 drivers/spi/spi-bcm2835.c | 408 ++++++++++++++++++++++++++++++++------
 drivers/spi/spi.c         |  18 +-
 3 files changed, 390 insertions(+), 74 deletions(-)

-- 
2.20.1


^ permalink raw reply	[flat|nested] 29+ messages in thread

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Thread overview: 29+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-03 10:10 [PATCH 00/10] Raspberry Pi SPI speedups Lukas Wunner
2019-08-03 10:10 ` [PATCH 01/10] dmaengine: bcm2835: Allow reusable descriptors Lukas Wunner
2019-08-08 12:30   ` Vinod Koul
2019-08-03 10:10 ` [PATCH 04/10] spi: bcm2835: Drop dma_pending flag Lukas Wunner
2019-08-03 10:10 ` [PATCH 05/10] spi: bcm2835: Work around DONE bit erratum Lukas Wunner
2019-08-11 19:45   ` Stefan Wahren
2019-08-11 19:57     ` Lukas Wunner
2019-08-11 20:29       ` Eric Anholt
2019-08-19 19:20       ` Stefan Wahren
2019-08-03 10:10 ` [PATCH 09/10] dmaengine: bcm2835: Avoid accessing memory when copying zeroes Lukas Wunner
2019-08-08 12:31   ` Vinod Koul
2019-08-03 10:10 ` [PATCH 07/10] spi: bcm2835: Speed up TX-only DMA transfers by clearing RX FIFO Lukas Wunner
2019-08-03 10:10 ` [PATCH 06/10] spi: bcm2835: Cache CS register value for ->prepare_message() Lukas Wunner
2019-08-03 10:10 ` [PATCH 02/10] dmaengine: bcm2835: Allow cyclic transactions without interrupt Lukas Wunner
2019-08-08 12:30   ` Vinod Koul
2019-08-03 10:10 ` [PATCH 08/10] dmaengine: bcm2835: Document struct bcm2835_dmadev Lukas Wunner
2019-08-08 12:31   ` Vinod Koul
2019-08-03 10:10 ` [PATCH 10/10] spi: bcm2835: Speed up RX-only DMA transfers by zero-filling TX FIFO Lukas Wunner
2019-08-03 10:10 ` [PATCH 03/10] spi: Guarantee cacheline alignment of driver-private data Lukas Wunner
2019-09-10 11:29   ` Mark Brown
2019-08-03 16:01 ` [PATCH 00/10] Raspberry Pi SPI speedups Noralf Trønnes
2019-08-11 19:50 ` Stefan Wahren
2019-08-11 19:52   ` Lukas Wunner
2019-08-19 19:22 ` Stefan Wahren
2019-08-21 15:21 ` kernel
2019-08-24 10:33 ` Lukas Wunner
2019-09-07  9:06 ` Lukas Wunner
2019-09-09 16:56   ` Mark Brown
2019-09-10 11:21   ` Mark Brown

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