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- From 586f87307e75552292cfc6c76b81cd38d5ec31e2 Mon Sep 17 00:00:00 2001
- From: Nick Hollinghurst <[email protected]>
- Date: Mon, 4 Sep 2023 10:57:47 +0100
- Subject: [PATCH] spi: spi-gpio: Implement spidelay when requested bit rate <=
- 1 Mbps
- Formerly the delay was omitted as bit-banged SPI seldom achieved
- even one Mbit/s; but some modern platforms can run faster, and
- some SPI devices may need to be clocked slower.
- Signed-off-by: Nick Hollinghurst <[email protected]>
- ---
- drivers/spi/spi-gpio.c | 18 ++++++++++++------
- 1 file changed, 12 insertions(+), 6 deletions(-)
- --- a/drivers/spi/spi-gpio.c
- +++ b/drivers/spi/spi-gpio.c
- @@ -11,12 +11,12 @@
- #include <linux/gpio/consumer.h>
- #include <linux/of.h>
- #include <linux/of_device.h>
- +#include <linux/delay.h>
-
- #include <linux/spi/spi.h>
- #include <linux/spi/spi_bitbang.h>
- #include <linux/spi/spi_gpio.h>
-
- -
- /*
- * This bitbanging SPI master driver should help make systems usable
- * when a native hardware SPI engine is not available, perhaps because
- @@ -111,12 +111,18 @@ static inline int getmiso(const struct s
- }
-
- /*
- - * 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.
- + * Generic bit-banged GPIO SPI might free-run at something in the range
- + * 1Mbps ~ 10Mbps (depending on the platform), and some SPI devices may
- + * need to be clocked at a lower rate. ndelay() is often implemented by
- + * udelay() with rounding up, so do the delay only for nsecs >= 500
- + * (<= 1Mbps). The conditional test adds a small overhead.
- */
- -#define spidelay(nsecs) do {} while (0)
- +
- +static inline void spidelay(unsigned long nsecs)
- +{
- + if (nsecs >= 500)
- + ndelay(nsecs);
- +}
-
- #include "spi-bitbang-txrx.h"
-
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