target/linux/bcm27xx/patches-6.1/950-0901-spi-spi-gpio-Implement-spidelay-when-requested-bit-r.patch

   1 From 586f87307e75552292cfc6c76b81cd38d5ec31e2 Mon Sep 17 00:00:00 2001
   2 From: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
   3 Date: Mon, 4 Sep 2023 10:57:47 +0100
   4 Subject: [PATCH] spi: spi-gpio: Implement spidelay when requested bit rate <=
   5  1 Mbps
   6
   7 Formerly the delay was omitted as bit-banged SPI seldom achieved
   8 even one Mbit/s; but some modern platforms can run faster, and
   9 some SPI devices may need to be clocked slower.
  10
  11 Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
  12 ---
  13  drivers/spi/spi-gpio.c | 18 ++++++++++++------
  14  1 file changed, 12 insertions(+), 6 deletions(-)
  15
  16 --- a/drivers/spi/spi-gpio.c
  17 +++ b/drivers/spi/spi-gpio.c
  18 @@ -11,12 +11,12 @@
  19  #include <linux/gpio/consumer.h>
  20  #include <linux/of.h>
  21  #include <linux/of_device.h>
  22 +#include <linux/delay.h>
  23
  24  #include <linux/spi/spi.h>
  25  #include <linux/spi/spi_bitbang.h>
  26  #include <linux/spi/spi_gpio.h>
  27
  28 -
  29  /*
  30   * This bitbanging SPI master driver should help make systems usable
  31   * when a native hardware SPI engine is not available, perhaps because
  32 @@ -111,12 +111,18 @@ static inline int getmiso(const struct s
  33  }
  34
  35  /*
  36 - * NOTE:  this clocks "as fast as we can".  It "should" be a function of the
  37 - * requested device clock.  Software overhead means we usually have trouble
  38 - * reaching even one Mbit/sec (except when we can inline bitops), so for now
  39 - * we'll just assume we never need additional per-bit slowdowns.
  40 + * Generic bit-banged GPIO SPI might free-run at something in the range
  41 + * 1Mbps ~ 10Mbps (depending on the platform), and some SPI devices may
  42 + * need to be clocked at a lower rate. ndelay() is often implemented by
  43 + * udelay() with rounding up, so do the delay only for nsecs >= 500
  44 + * (<= 1Mbps). The conditional test adds a small overhead.
  45   */
  46 -#define spidelay(nsecs)        do {} while (0)
  47 +
  48 +static inline void spidelay(unsigned long nsecs)
  49 +{
  50 +       if (nsecs >= 500)
  51 +               ndelay(nsecs);
  52 +}
  53
  54  #include "spi-bitbang-txrx.h"
  55