qualcommax: add spidelay patch

Copy the spidelay patch from
target/linux/bcm27xx/patches-6.18/0314-spi-spi-gpio-Implement-spidelay-when-requested-bit-r.patch
to be able to reduce the frequency of spi-gpio.

Signed-off-by: Leonard Anderweit <leonard.anderweit@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/25056
Signed-off-by: Robert Marko <robimarko@gmail.com>

target/linux/qualcommax/patches-6.18/0314-spi-spi-gpio-Implement-spidelay-when-requested-bit-r.patch

@@ -0,0 +1,49 @@
+From 175216a5eaeb474c82904eb7ec440091c87588d8 Mon Sep 17 00:00:00 2001
+From: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
+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 <nick.hollinghurst@raspberrypi.com>
+---
+ drivers/spi/spi-gpio.c | 17 ++++++++++++-----
+ 1 file changed, 12 insertions(+), 5 deletions(-)
+
+--- a/drivers/spi/spi-gpio.c
++++ b/drivers/spi/spi-gpio.c
+@@ -11,6 +11,7 @@
+ #include <linux/module.h>
+ #include <linux/platform_device.h>
+ #include <linux/property.h>
++#include <linux/delay.h>
+ 
+ #include <linux/spi/spi.h>
+ #include <linux/spi/spi_bitbang.h>
+@@ -80,12 +81,18 @@ 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"
+