usb_spi: add API for reading arbitrary AP flash locations

This API will provide support to the AP RO verification
implementation. The size of data read in one transaction is limited by
SPI_HASH_CHUNK size.

BUG=b:199904580, b:200736744
TEST=tested along with AP RO verification implementation.

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Change-Id: Id4da2add2ce1202d979627dde40325b583004fc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3172254
Reviewed-by: Andrey Pronin <apronin@chromium.org>

2 files changed, 31 insertions, 0 deletions

diff --git a/board/cr50/usb_spi.c b/board/cr50/usb_spi.c
index 6876272297..4aede92f19 100644
--- a/board/cr50/usb_spi.c
+++ b/board/cr50/usb_spi.c
@@ -683,6 +683,26 @@ int usb_spi_sha256_start(struct sha256_ctx *ctx)
 	return EC_SUCCESS;
 }
 
+int usb_spi_read_buffer(void *buf, unsigned int offset,  size_t bytes)
+{
+	uint8_t *p = buf;
+
+	while (bytes) {
+		const int this_chunk = MIN(bytes, SPI_HASH_CHUNK_SIZE);
+
+		/* Read the data */
+		if (spi_read_chunk(p, offset, this_chunk) != EC_SUCCESS) {
+			CPRINTS("%s: read error at 0x%x", __func__, offset);
+			return VENDOR_RC_READ_FLASH_FAIL;
+		}
+
+		bytes -= this_chunk;
+		offset += this_chunk;
+		p += this_chunk;
+	}
+	return EC_SUCCESS;
+}
+
 int usb_spi_sha256_update(struct sha256_ctx *ctx, uint32_t offset,
 			  uint32_t size)
 {
diff --git a/board/cr50/usb_spi_board.h b/board/cr50/usb_spi_board.h
index 1c40f0814d..7549b98f7f 100644
--- a/board/cr50/usb_spi_board.h
+++ b/board/cr50/usb_spi_board.h
@@ -9,3 +9,14 @@ int usb_spi_sha256_update(struct sha256_ctx *ctx, uint32_t offset,
 			  uint32_t size);
 void usb_spi_sha256_final(struct sha256_ctx *ctx, void *digest,
 			  size_t digest_size);
+
+/**
+ * Returns the content of SPI flash
+ *
+ * @param buf Buffer to write flash contents
+ * @param offset Flash offset to start reading from
+ * @param bytes Number of bytes to read.
+ *
+ * @return EC_SUCCESS, or non-zero if any error.
+ */
+int usb_spi_read_buffer(void *buf, unsigned int offset,  size_t bytes);