sw/device/lib/dif/dif_csrng_shared.c

// Copyright lowRISC contributors.
// Licensed under the Apache License, Version 2.0, see LICENSE for details.
// SPDX-License-Identifier: Apache-2.0

#include "sw/device/lib/dif/dif_csrng_shared.h"

#include "sw/device/lib/base/multibits.h"

// The application command header is not specified as a register in the
// hardware specification, so the fields are mapped here by hand. The
// command register also accepts arbitrary 32bit data.
static const bitfield_field32_t kAppCmdFieldFlag0 = {.mask = 0xf, .index = 8};
static const bitfield_field32_t kAppCmdFieldCmdId = {.mask = 0xf, .index = 0};
static const bitfield_field32_t kAppCmdFieldCmdLen = {.mask = 0xf, .index = 4};
static const bitfield_field32_t kAppCmdFieldGlen = {.mask = 0x7ffff,
                                                    .index = 12};

uint32_t csrng_cmd_header_build(
    csrng_app_cmd_id_t id, dif_csrng_entropy_src_toggle_t entropy_src_enable,
    uint32_t cmd_len, uint32_t generate_len) {
  uint32_t reg = bitfield_field32_write(0, kAppCmdFieldCmdId, id);
  reg = bitfield_field32_write(reg, kAppCmdFieldCmdLen, cmd_len);
  reg = bitfield_field32_write(
      reg, kAppCmdFieldFlag0,
      (entropy_src_enable == kDifCsrngEntropySrcToggleDisable
           ? kMultiBitBool4True
           : kMultiBitBool4False));
  reg = bitfield_field32_write(reg, kAppCmdFieldGlen, generate_len);
  return reg;
}

dif_result_t csrng_send_app_cmd(mmio_region_t base_addr, ptrdiff_t offset,
                                csrng_app_cmd_t cmd) {
  // Ensure the `seed_material` array is word-aligned, so it can be loaded to a
  // CPU register with natively aligned loads.
  if (cmd.seed_material != NULL &&
      misalignment32_of((uintptr_t)cmd.seed_material->seed_material) != 0) {
    return kDifBadArg;
  }

  uint32_t cmd_len =
      cmd.seed_material == NULL ? 0 : cmd.seed_material->seed_material_len;
  if (cmd_len & ~kAppCmdFieldCmdLen.mask) {
    return kDifBadArg;
  }

  mmio_region_write32(base_addr, offset,
                      csrng_cmd_header_build(cmd.id, cmd.entropy_src_enable,
                                             cmd_len, cmd.generate_len));
  for (size_t i = 0; i < cmd_len; ++i) {
    mmio_region_write32(base_addr, offset, cmd.seed_material->seed_material[i]);
  }
  return kDifOk;
}