From 1eed29df472a33bba013d5a2ea2f9e32f4414397 Mon Sep 17 00:00:00 2001 From: Haavard Skinnemoen Date: Wed, 6 Feb 2008 01:38:11 -0800 Subject: [PATCH] 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 Signed-off-by: David Brownell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/spi/atmel_spi.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c index ff10808183a3..b09d33678dd8 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; -- 2.11.0