Implement the SPI-GPIO delay function for busses that need speed limitation.
If the special all-inline API is used, the delay is disabled at compiletime.
Otherwise it's an unlikely condition that can be disabled via max_speed_hz.
So it should have minimal or zero impact on the speed of implementations
without delay.
Signed-off-by: Michael Buesch <m...@bu3sch.de>
---
I need this delay when using a slow microcontroller attached via SPI-GPIO
to a fast embedded router device.
Index: linux-2.6/drivers/spi/spi_gpio.c
===================================================================
--- linux-2.6.orig/drivers/spi/spi_gpio.c 2009-02-15 16:27:16.000000000
+0100
+++ linux-2.6/drivers/spi/spi_gpio.c 2009-02-15 19:19:36.000000000 +0100
@@ -21,6 +21,7 @@
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/gpio.h>
+#include <linux/delay.h>
#include <linux/spi/spi.h>
#include <linux/spi/spi_bitbang.h>
@@ -69,6 +70,7 @@ struct spi_gpio {
* #define SPI_MOSI_GPIO 120
* #define SPI_SCK_GPIO 121
* #define SPI_N_CHIPSEL 4
+ * #undef NEED_SPIDELAY
* #include "spi_gpio.c"
*/
@@ -76,6 +78,7 @@ struct spi_gpio {
#define DRIVER_NAME "spi_gpio"
#define GENERIC_BITBANG /* vs tight inlines */
+#define NEED_SPIDELAY 1
/* all functions referencing these symbols must define pdata */
#define SPI_MISO_GPIO ((pdata)->miso)
@@ -120,12 +123,20 @@ static inline int getmiso(const struct s
#undef pdata
/*
- * 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
- * reaching even one Mbit/sec (except when we can inline bitops), so for now
- * we'll just assume we never need additional per-bit slowdowns.
+ * NOTE: to clock "as fast as we can", set spi_device.max_speed_hz
+ * and spi_transfer.speed_hz to 0.
+ * Otherwise this is a function of the requested device clock.
+ * Software overhead means we usually have trouble
+ * reaching even one Mbit/sec (except when we can inline bitops). So on small
+ * embedded devices with fast SPI slaves you usually don't need a delay.
*/
-#define spidelay(nsecs) do {} while (0)
+static inline void spidelay(unsigned nsecs)
+{
+#ifdef NEED_SPIDELAY
+ if (unlikely(nsecs))
+ ndelay(nsecs);
+#endif /* NEED_SPIDELAY */
+}
#define EXPAND_BITBANG_TXRX
#include <linux/spi/spi_bitbang.h>
--
Greetings, Michael.
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