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| author | Haavard Skinnemoen <hskinnemoen@atmel.com> | 2008-02-06 01:38:11 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-06 10:41:10 -0800 |
| commit | 1eed29df472a33bba013d5a2ea2f9e32f4414397 (patch) | |
| tree | 857d8c03baab8c845cd94cd601caab05e57dcb5b /drivers/spi | |
| parent | 3c72426f0539c1abce17918d1456f7a6a5a11f90 (diff) | |
| download | kernel_samsung_smdk4412-1eed29df472a33bba013d5a2ea2f9e32f4414397.tar.gz kernel_samsung_smdk4412-1eed29df472a33bba013d5a2ea2f9e32f4414397.tar.bz2 kernel_samsung_smdk4412-1eed29df472a33bba013d5a2ea2f9e32f4414397.zip | |
atmel_spi throughput improvement
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@atmel.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/atmel_spi.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c index ff10808183a..b09d33678dd 100644 --- a/drivers/spi/atmel_spi.c +++ b/drivers/spi/atmel_spi.c @@ -490,9 +490,14 @@ static int atmel_spi_setup(struct spi_device *spi) 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; |