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56 lines
1.9 KiB
Diff
56 lines
1.9 KiB
Diff
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From 586f87307e75552292cfc6c76b81cd38d5ec31e2 Mon Sep 17 00:00:00 2001
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From: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
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Date: Mon, 4 Sep 2023 10:57:47 +0100
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Subject: [PATCH] spi: spi-gpio: Implement spidelay when requested bit rate <=
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1 Mbps
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Formerly the delay was omitted as bit-banged SPI seldom achieved
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even one Mbit/s; but some modern platforms can run faster, and
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some SPI devices may need to be clocked slower.
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Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
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---
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drivers/spi/spi-gpio.c | 18 ++++++++++++------
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1 file changed, 12 insertions(+), 6 deletions(-)
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--- a/drivers/spi/spi-gpio.c
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+++ b/drivers/spi/spi-gpio.c
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@@ -11,12 +11,12 @@
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#include <linux/gpio/consumer.h>
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#include <linux/of.h>
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#include <linux/of_device.h>
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+#include <linux/delay.h>
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#include <linux/spi/spi.h>
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#include <linux/spi/spi_bitbang.h>
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#include <linux/spi/spi_gpio.h>
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-
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/*
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* This bitbanging SPI master driver should help make systems usable
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* when a native hardware SPI engine is not available, perhaps because
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@@ -111,12 +111,18 @@ static inline int getmiso(const struct s
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}
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/*
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- * NOTE: this clocks "as fast as we can". It "should" be a function of the
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- * requested device clock. Software overhead means we usually have trouble
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- * reaching even one Mbit/sec (except when we can inline bitops), so for now
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- * we'll just assume we never need additional per-bit slowdowns.
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+ * Generic bit-banged GPIO SPI might free-run at something in the range
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+ * 1Mbps ~ 10Mbps (depending on the platform), and some SPI devices may
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+ * need to be clocked at a lower rate. ndelay() is often implemented by
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+ * udelay() with rounding up, so do the delay only for nsecs >= 500
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+ * (<= 1Mbps). The conditional test adds a small overhead.
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*/
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-#define spidelay(nsecs) do {} while (0)
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+
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+static inline void spidelay(unsigned long nsecs)
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+{
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+ if (nsecs >= 500)
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+ ndelay(nsecs);
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+}
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#include "spi-bitbang-txrx.h"
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