--- /dev/null
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for DS-2502 One wire "Add only Memory".
+ *
+ * The chip has 4 pages of 32 bytes.
+ * In addition it has 8 out of band status bytes that are used, by software,
+ * as page redirection bytes by an algorithm described in the data sheet.
+ * This is useful since data cannot be erased once written but it can be
+ * "patched" up to four times by switching pages.
+ *
+ * So, when a read request is entirely in the first page automatically
+ * apply the page redirection bytes (which allows the device to be seen as
+ * a 32 byte PROM, writable 4 times).
+ *
+ * If the read request is outside of or larger than the first page then read
+ * the raw data (which allows the device to be seen as a 128 byte PROM,
+ * writable once).
+ *
+ * Copyright (c) 2018 Flowbird
+ * Martin Fuzzey <martin.fuzzey@flowbird.group>
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <linux/err.h>
+#include <w1-eeprom.h>
+#include <w1.h>
+
+#define DS2502_PAGE_SIZE 32
+#define DS2502_PAGE_COUNT 4
+#define DS2502_STATUS_SIZE 8
+
+#define DS2502_CMD_READ_STATUS 0xAA
+#define DS2502_CMD_READ_GEN_CRC 0xC3
+
+/* u-boot crc8() is CCITT CRC8, we need x^8 + x^5 + x^4 + 1 LSB first */
+static unsigned int ds2502_crc8(const u8 *buf, int len)
+{
+ static const u8 poly = 0x8C; /* (1 + x^4 + x^5) + x^8 */
+ u8 crc = 0;
+ int i;
+
+ for (i = 0; i < len; i++) {
+ u8 data = buf[i];
+ int j;
+
+ for (j = 0; j < 8; j++) {
+ u8 mix = (crc ^ data) & 1;
+
+ crc >>= 1;
+ if (mix)
+ crc ^= poly;
+ data >>= 1;
+ }
+ }
+ return crc;
+}
+
+static int ds2502_read(struct udevice *dev, u8 cmd,
+ int bytes_in_page, int pos,
+ u8 *buf, int bytes_for_user)
+{
+ int retry;
+ int ret = 0;
+
+ for (retry = 0; retry < 3; retry++) {
+ u8 pagebuf[DS2502_PAGE_SIZE + 1]; /* 1 byte for CRC8 */
+ u8 crc;
+ int i;
+
+ ret = w1_reset_select(dev);
+ if (ret)
+ return ret;
+
+ /* send read to end of page and generate CRC command */
+ pagebuf[0] = cmd;
+ pagebuf[1] = pos & 0xff;
+ pagebuf[2] = pos >> 8;
+ crc = ds2502_crc8(pagebuf, 3);
+ for (i = 0; i < 3; i++)
+ w1_write_byte(dev, pagebuf[i]);
+
+ /* Check command CRC */
+ ret = w1_read_byte(dev);
+ if (ret < 0) {
+ dev_dbg(dev, "Error %d reading command CRC\n", ret);
+ continue;
+ }
+
+ if (ret != crc) {
+ dev_dbg(dev,
+ "bad CRC8 for cmd %02x got=%02X exp=%02X\n",
+ cmd, ret, crc);
+ ret = -EIO;
+ continue;
+ }
+
+ /* read data and check CRC */
+ ret = w1_read_buf(dev, pagebuf, bytes_in_page + 1);
+ if (ret < 0) {
+ dev_dbg(dev, "Error %d reading data\n", ret);
+ continue;
+ }
+
+ crc = ds2502_crc8(pagebuf, bytes_in_page);
+ if (crc == pagebuf[bytes_in_page]) {
+ memcpy(buf, pagebuf, bytes_for_user);
+ ret = 0;
+ break;
+ }
+ dev_dbg(dev, "Bad CRC8 got=%02X exp=%02X pos=%04X\n",
+ pagebuf[bytes_in_page], crc, pos);
+ ret = -EIO;
+ }
+
+ return ret;
+}
+
+static inline int ds2502_read_status_bytes(struct udevice *dev, u8 *buf)
+{
+ return ds2502_read(dev, DS2502_CMD_READ_STATUS,
+ DS2502_STATUS_SIZE, 0,
+ buf, DS2502_STATUS_SIZE);
+}
+
+/*
+ * Status bytes (from index 1) contain 1's complement page indirection
+ * So for N writes:
+ * N=1: ff ff ff ff ff ff ff 00
+ * N=2: ff fe ff ff ff ff ff 00
+ * N=3: ff fe fd ff ff ff ff 00
+ * N=4: ff fe fd fc ff ff ff 00
+ */
+static int ds2502_indirect_page(struct udevice *dev, u8 *status, int page)
+{
+ int page_seen = 0;
+
+ do {
+ u8 sb = status[page + 1];
+
+ if (sb == 0xff)
+ break;
+
+ page = ~sb & 0xff;
+
+ if (page >= DS2502_PAGE_COUNT) {
+ dev_err(dev,
+ "Illegal page redirection status byte %02x\n",
+ sb);
+ return -EINVAL;
+ }
+
+ if (page_seen & (1 << page)) {
+ dev_err(dev, "Infinite loop in page redirection\n");
+ return -EINVAL;
+ }
+
+ page_seen |= (1 << page);
+ } while (1);
+
+ return page;
+}
+
+static int ds2502_read_buf(struct udevice *dev, unsigned int offset,
+ u8 *buf, unsigned int count)
+{
+ unsigned int min_page = offset / DS2502_PAGE_SIZE;
+ unsigned int max_page = (offset + count - 1) / DS2502_PAGE_SIZE;
+ int xfered = 0;
+ u8 status_bytes[DS2502_STATUS_SIZE];
+ int i;
+ int ret;
+
+ if (min_page >= DS2502_PAGE_COUNT || max_page >= DS2502_PAGE_COUNT)
+ return -EINVAL;
+
+ if (min_page == 0 && max_page == 0) {
+ ret = ds2502_read_status_bytes(dev, status_bytes);
+ if (ret)
+ return ret;
+ } else {
+ /* Dummy one to one page redirection */
+ memset(status_bytes, 0xff, sizeof(status_bytes));
+ }
+
+ for (i = min_page; i <= max_page; i++) {
+ int page;
+ int pos;
+ int bytes_in_page;
+ int bytes_for_user;
+
+ page = ds2502_indirect_page(dev, status_bytes, i);
+ if (page < 0)
+ return page;
+ dev_dbg(dev, "page logical %d => physical %d\n", i, page);
+
+ pos = page * DS2502_PAGE_SIZE;
+ if (i == min_page)
+ pos += offset % DS2502_PAGE_SIZE;
+
+ bytes_in_page = DS2502_PAGE_SIZE - (pos % DS2502_PAGE_SIZE);
+
+ if (i == max_page)
+ bytes_for_user = count - xfered;
+ else
+ bytes_for_user = bytes_in_page;
+
+ ret = ds2502_read(dev, DS2502_CMD_READ_GEN_CRC,
+ bytes_in_page, pos,
+ &buf[xfered], bytes_for_user);
+ if (ret < 0)
+ return ret;
+
+ xfered += bytes_for_user;
+ }
+
+ return 0;
+}
+
+static int ds2502_probe(struct udevice *dev)
+{
+ struct w1_device *w1;
+
+ w1 = dev_get_parent_platdata(dev);
+ w1->id = 0;
+ return 0;
+}
+
+static const struct w1_eeprom_ops ds2502_ops = {
+ .read_buf = ds2502_read_buf,
+};
+
+static const struct udevice_id ds2502_id[] = {
+ { .compatible = "maxim,ds2502", .data = W1_FAMILY_DS2502 },
+ { },
+};
+
+U_BOOT_DRIVER(ds2502) = {
+ .name = "ds2502",
+ .id = UCLASS_W1_EEPROM,
+ .of_match = ds2502_id,
+ .ops = &ds2502_ops,
+ .probe = ds2502_probe,
+};
projects / u-boot.git / commitdiff