The patch titled
atmel_spi throughput improvement
has been added to the -mm tree. Its filename is
atmel_spi-throughput-improvement.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: atmel_spi throughput improvement
From: Haavard Skinnemoen <hskinnemoen@xxxxxxxxx>
Don't insert (undesirable) delays between consecutive words (DLYBCT) or when
activating chipselects (DLYBS).
Removing the between-word delays improves the performance of bulk transfers
(such as mtd_dataflash, m25p80, mmc_spi) significantly. In one test, the
improvement was a factor of more than eight!
(The large DLYBCT value came from the legacy at91 SPI driver, and it's not
clear why it used such a huge value.)
Signed-off-by: Haavard Skinnemoen <hskinnemoen@xxxxxxxxx>
Signed-off-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/spi/atmel_spi.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff -puN drivers/spi/atmel_spi.c~atmel_spi-throughput-improvement drivers/spi/atmel_spi.c
--- a/drivers/spi/atmel_spi.c~atmel_spi-throughput-improvement
+++ a/drivers/spi/atmel_spi.c
@@ -490,9 +490,14 @@ static int atmel_spi_setup(struct spi_de
if (!(spi->mode & SPI_CPHA))
csr |= SPI_BIT(NCPHA);
- /* TODO: DLYBS and DLYBCT */
- csr |= SPI_BF(DLYBS, 10);
- csr |= SPI_BF(DLYBCT, 10);
+ /* DLYBS is mostly irrelevant since we manage chipselect using GPIOs.
+ *
+ * DLYBCT would add delays between words, slowing down transfers.
+ * It could potentially be useful to cope with DMA bottlenecks, but
+ * in those cases it's probably best to just use a lower bitrate.
+ */
+ csr |= SPI_BF(DLYBS, 0);
+ csr |= SPI_BF(DLYBCT, 0);
/* chipselect must have been muxed as GPIO (e.g. in board setup) */
npcs_pin = (unsigned int)spi->controller_data;
_
Patches currently in -mm which might be from hskinnemoen@xxxxxxxxx are
origin.patch
atmel_spi-labels-gpios-better.patch
atmel_spi-throughput-improvement.patch
git-avr32.patch
git-mtd.patch
read_current_time-cleanups.patch
generic-gpio-gpio_chip-support.patch
avr32-uses-gpio_chip.patch
mcp23s08-spi-gpio-expander.patch
mcp23s08-spi-gpio-expander-checkpatch-fixes.patch
sanitize-the-type-of-struct-useru_ar0.patch
add-cmpxchg_local-to-avr32.patch
atmel_spi-chains-dma-transfers.patch
-
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