Introduce a Kconfig option, SLOWER_SPI_GPIO, that enables a spidelay implementation of ndelay when defined.
This is based off of the patch proposed by Michael Buesch [1]. Whereas that patch required slave's set their spi_device.max_speed_hz and spi_transfer.speed_hz to 0 to obtain 'as fast as we can transfers' this patch keeps the default of 'as fast as we can' for any GPIO SPI master unless the proposed Kconfig option is enabled. Signed-off-by: Ben Gardiner <bengardi...@nanometrics.ca> Reviewed-by: Dan Sharon <dansha...@nanometrics.ca> Reviewed-by: Chris Cordahi <chriscord...@nanometrics.ca> CC: Michael Buesch <m...@bu3sch.de> [1] http://article.gmane.org/gmane.comp.embedded.openwrt.devel/2854 --- This patch was rebased to 6656b3fc8aba2eb7ca00c06c7fe4917938b0b652 of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git Testing was performed using the GPIOs of a da850evm. I registered an spi-gpio instance and a slave device with a transfer speed of 500Hz (the slowest possible speed on ARM since the udelay max is 2ms): ... static struct spi_gpio_platform_data bb_spi_gpio_pdata = { .sck = SPIG_CLK, .mosi = SPIG_SIMO, .miso = SPIG_SOMI, .num_chipselect = 1, }; static struct platform_device bb_spi_gpio = { .name = "spi_gpio", .id = 0, .dev = { .platform_data = &bb_spi_gpio_pdata, }, }; static struct spi_board_info bb_spi_devices[] = { { .modalias = "spidev", .max_speed_hz = 500, .bus_num = 0, .chip_select = 0, .mode = SPI_MODE_0, }, }; ... Without SLOWER_SPI_GPIO=y a spi transfer using 'echo a > /dev/spidev0.0' resulted in a ~700kHz SCLK signal. With SLOWER_SPI_GPIO=y a spi transfer using 'echo a > /dev/spidev0.0' resulted in a ~500Hz SCLK signal. --- drivers/spi/Kconfig | 17 +++++++++++++++++ drivers/spi/spi_gpio.c | 5 +++++ 2 files changed, 22 insertions(+), 0 deletions(-) diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig index 78f9fd0..0570dcd 100644 --- a/drivers/spi/Kconfig +++ b/drivers/spi/Kconfig @@ -143,6 +143,23 @@ config SPI_GPIO GPIO operations, you should be able to leverage that for better speed with a custom version of this driver; see the source code. +config SLOWER_SPI_GPIO + bool "Enable delays in the GPIO-based bitbanging SPI Master" + default n + depends on SPI_GPIO + help + The GPIO bitbanging SPI master driver will run without any delays if this + option is not set. This option will enable the use of delays in the + operation of the GPIO bitbanging SPI master implementation to honour the + maximum speed of very slow devices. + + To configure slow speed devices your board-specific setup logic must also + provide platform data assigning the speed for a device on a given chip + select of the GPIO bitbanging SPI master. + + If your platform requires SPI buses driven at slow speeds select yes. If + in doubt, select no. + config SPI_IMX_VER_IMX1 def_bool y if SOC_IMX1 diff --git a/drivers/spi/spi_gpio.c b/drivers/spi/spi_gpio.c index 63e51b0..b31fddd 100644 --- a/drivers/spi/spi_gpio.c +++ b/drivers/spi/spi_gpio.c @@ -19,6 +19,7 @@ */ #include <linux/kernel.h> #include <linux/init.h> +#include <linux/delay.h> #include <linux/platform_device.h> #include <linux/gpio.h> @@ -119,6 +120,9 @@ static inline int getmiso(const struct spi_device *spi) #undef pdata +#if defined(CONFIG_SLOWER_SPI_GPIO) +#define spidelay(nsecs) ndelay(nsecs) +#else /* * NOTE: this clocks "as fast as we can". It "should" be a function of the * requested device clock. Software overhead means we usually have trouble @@ -126,6 +130,7 @@ static inline int getmiso(const struct spi_device *spi) * we'll just assume we never need additional per-bit slowdowns. */ #define spidelay(nsecs) do {} while (0) +#endif #include "spi_bitbang_txrx.h" -- 1.7.0.4 ------------------------------------------------------------------------------ Beautiful is writing same markup. Internet Explorer 9 supports standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 & L3. Spend less time writing and rewriting code and more time creating great experiences on the web. Be a part of the beta today http://p.sf.net/sfu/msIE9-sfdev2dev _______________________________________________ spi-devel-general mailing list spi-devel-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spi-devel-general
