[sw/silicon_creator] Constrain otp_read to aligned reads

Update the signature for otp_read as a follow-up to
https://github.com/lowRISC/opentitan/pull/7000/files#r652890537

Signed-off-by: Jon Flatley <jflat@google.com>

sw/device/silicon_creator/lib/drivers/otp.c

diff --git a/sw/device/silicon_creator/lib/drivers/otp.c b/sw/device/silicon_creator/lib/drivers/otp.c
index 155e584..ebcac8e 100644
--- a/sw/device/silicon_creator/lib/drivers/otp.c
+++ b/sw/device/silicon_creator/lib/drivers/otp.c
@@ -28,18 +28,9 @@
   return value;
 }
 
-rom_error_t otp_read(uint32_t address, void *data, size_t len) {
-  // TODO Update to use alignment utility functions.
-  // https://github.com/lowRISC/opentitan/issues/6112
-  if (address % alignof(uint32_t) != 0 || len % sizeof(uint32_t) != 0) {
-    return kErrorOtpBadAlignment;
-  }
-
+void otp_read(uint32_t address, uint32_t *data, size_t num_words) {
   uint32_t reg_offset = OTP_CTRL_SW_CFG_WINDOW_REG_OFFSET + address;
-  for (size_t i = 0; i < len; i += sizeof(uint32_t)) {
-    uint32_t word = sec_mmio_read32(kBase + reg_offset + i);
-    memcpy(data + i, &word, sizeof(uint32_t));
+  for (size_t i = 0; i < num_words; ++i) {
+    data[i] = sec_mmio_read32(kBase + reg_offset + i * sizeof(uint32_t));
   }
-
-  return kErrorOk;
 }

sw/device/silicon_creator/lib/drivers/otp.h

diff --git a/sw/device/silicon_creator/lib/drivers/otp.h b/sw/device/silicon_creator/lib/drivers/otp.h
index f444c5d..8b3de4a 100644
--- a/sw/device/silicon_creator/lib/drivers/otp.h
+++ b/sw/device/silicon_creator/lib/drivers/otp.h
@@ -37,18 +37,14 @@
 uint64_t otp_read64(uint32_t address);
 
 /**
- * Perform a blocking read of `len` bytes from the memory mapped software config
- * partitions. It is required that both `address` and `address` + `len` be
- * word-aligned.
+ * Perform a blocking read of `num_words` 32-bit words from the memory mapped
+ * software config partitions.
  *
  * @param address The address to read from offset from the start of OTP memory.
- * @param data The output buffer of at least length `len`.
- * @param len The number of bytes to read from OTP.
- * @return `kErrorOtpBadAlignment` if `address` or `address` + `len` are
- * misaligned, `kErrorOk` otherwise.
+ * @param data The output buffer of at least length `num_words`.
+ * @param num_words The number of 32-bit words to read from OTP.
  */
-OTP_WARN_UNUSED_RESULT
-rom_error_t otp_read(uint32_t address, void *data, size_t len);
+void otp_read(uint32_t address, uint32_t *data, size_t num_words);
 
 #ifdef __cplusplus
 }

sw/device/silicon_creator/lib/drivers/otp_unittest.cc

diff --git a/sw/device/silicon_creator/lib/drivers/otp_unittest.cc b/sw/device/silicon_creator/lib/drivers/otp_unittest.cc
index 3f707b6..6611425 100644
--- a/sw/device/silicon_creator/lib/drivers/otp_unittest.cc
+++ b/sw/device/silicon_creator/lib/drivers/otp_unittest.cc
@@ -4,6 +4,8 @@
 
 #include "sw/device/silicon_creator/lib/drivers/otp.h"
 
+#include <array>
+
 #include "gtest/gtest.h"
 #include "sw/device/lib/base/mmio.h"
 #include "sw/device/lib/testing/mask_rom_test.h"
@@ -15,6 +17,7 @@
 
 namespace otp_unittest {
 namespace {
+using ::testing::ElementsAre;
 using ::testing::ElementsAreArray;
 
 class OtpTest : public mask_rom_test::MaskRomTest {
@@ -45,7 +48,7 @@
   EXPECT_SEC_READ32(mmio_, base_ + offset_, 0x08090A0B);
 
   uint32_t value = 0;
-  EXPECT_EQ(otp_read(0, &value, sizeof(value)), kErrorOk);
+  otp_read(0, &value, 1);
   EXPECT_EQ(value, 0x08090A0B);
 }
 
@@ -53,9 +56,9 @@
   EXPECT_SEC_READ32(mmio_, base_ + offset_, 0x0C0D0E0F);
   EXPECT_SEC_READ32(mmio_, base_ + offset_ + 4, 0x08090A0B);
 
-  uint64_t value = 0;
-  EXPECT_EQ(otp_read(0, &value, sizeof(value)), kErrorOk);
-  EXPECT_EQ(value, 0x08090A0B0C0D0E0F);
+  std::array<uint32_t, 2> buf;
+  otp_read(0, buf.data(), 2);
+  EXPECT_THAT(buf, ElementsAre(0x0C0D0E0F, 0x08090A0B));
 }
 
 TEST_F(OtpReadTest, ReadLenN) {
@@ -63,21 +66,13 @@
     EXPECT_SEC_READ32(mmio_, base_ + offset_ + val * sizeof(uint32_t), val);
   }
 
-  std::vector<uint32_t> arr(16);
-  EXPECT_EQ(otp_read(0, &arr[0], arr.size() * sizeof(uint32_t)), kErrorOk);
+  std::array<uint32_t, 16> arr;
+  otp_read(0, arr.data(), arr.size());
 
-  std::vector<uint32_t> expected(arr.size());
+  std::array<uint32_t, 16> expected;
   std::iota(expected.begin(), expected.end(), 0);
   EXPECT_THAT(arr, ElementsAreArray(expected));
 }
 
-TEST_F(OtpReadTest, ReadLenNMisaligned) {
-  std::vector<uint32_t> arr(16);
-  EXPECT_EQ(otp_read(1, &arr[0], arr.size() * sizeof(uint32_t)),
-            kErrorOtpBadAlignment);
-  EXPECT_EQ(otp_read(0, &arr[0], arr.size() * sizeof(uint32_t) - 1),
-            kErrorOtpBadAlignment);
-}
-
 }  // namespace
 }  // namespace otp_unittest