From: Haavard Skinnemoen Date: Wed, 6 Feb 2008 09:38:11 +0000 (-0800) Subject: atmel_spi throughput improvement X-Git-Tag: v2.6.25-rc1~657 X-Git-Url: http://www.pilppa.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=1eed29df472a33bba013d5a2ea2f9e32f4414397;p=linux-2.6-omap-h63xx.git 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 --- 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;