src/drivers/spi/bitbang.c

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <console/console.h>
   4 #include <delay.h>
   5 #include <spi_bitbang.h>
   6 #include <types.h>
   7
   8 /* Set to 1 to dump all SPI transfers to the UART. */
   9 #define TRACE           0
  10 /*
  11  * In theory, this should work fine with 0 delay since the bus is fully clocked
  12  * by the master and the slave just needs to follow clock transitions whenever
  13  * they happen. We're not going to be "too fast" by bit-banging anyway. However,
  14  * if something doesn't work right, try increasing this value to slow it down.
  15  */
  16 #define HALF_CLOCK_US   0
  17
  18 int spi_bitbang_claim_bus(const struct spi_bitbang_ops *ops)
  19 {
  20         ops->set_cs(ops, 0);
  21         return 0;
  22 }
  23
  24 void spi_bitbang_release_bus(const struct spi_bitbang_ops *ops)
  25 {
  26         ops->set_cs(ops, 1);
  27 }
  28
  29 /* Implements a CPOL=0, CPH=0, MSB first 8-bit controller. */
  30 int spi_bitbang_xfer(const struct spi_bitbang_ops *ops, const void *dout,
  31                      size_t bytes_out, void *din, size_t bytes_in)
  32 {
  33         if (TRACE) {
  34                 if (bytes_in && bytes_out)
  35                         printk(BIOS_SPEW, "!");
  36                 else if (bytes_in)
  37                         printk(BIOS_SPEW, "<");
  38                 else if (bytes_out)
  39                         printk(BIOS_SPEW, ">");
  40         }
  41
  42         while (bytes_out || bytes_in) {
  43                 int i;
  44                 uint8_t in_byte = 0, out_byte = 0;
  45                 if (bytes_out) {
  46                         out_byte = *(const uint8_t *)dout++;
  47                         bytes_out--;
  48                         if (TRACE)
  49                                 printk(BIOS_SPEW, "%02x", out_byte);
  50                 }
  51                 for (i = 7; i >= 0; i--) {
  52                         ops->set_mosi(ops, !!(out_byte & (1 << i)));
  53                         if (HALF_CLOCK_US)
  54                                 udelay(HALF_CLOCK_US);
  55                         ops->set_clk(ops, 1);
  56                         in_byte |= !!ops->get_miso(ops) << i;
  57                         if (HALF_CLOCK_US)
  58                                 udelay(HALF_CLOCK_US);
  59                         ops->set_clk(ops, 0);
  60                 }
  61                 if (bytes_in) {
  62                         *(uint8_t *)din++ = in_byte;
  63                         bytes_in--;
  64                         if (TRACE)
  65                                 printk(BIOS_SPEW, "%02x", in_byte);
  66                 }
  67         }
  68
  69         if (TRACE)
  70                 printk(BIOS_SPEW, "\n");
  71         return 0;
  72 }