mtd: cfi: AMD/Fujitsu compatibles: add panic write support

This allows the mtdoops driver to work on flash chips using the
AMD/Fujitsu compatible command set.

As the code comments note, the locks used throughout the normal code
paths in the driver are ignored, so that the chance of writing out the
kernel's last messages are maximized.
Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/chips/cfi_cmdset_0002.c

@@ -59,6 +59,9 @@ static void cfi_amdstd_resume (struct mtd_info *);
 static int cfi_amdstd_reboot(struct notifier_block *, unsigned long, void *);
 static int cfi_amdstd_secsi_read (struct mtd_info *, loff_t, size_t, size_t *, u_char *);
 
+static int cfi_amdstd_panic_write(struct mtd_info *mtd, loff_t to, size_t len,
+				  size_t *retlen, const u_char *buf);
+
 static void cfi_amdstd_destroy(struct mtd_info *);
 
 struct mtd_info *cfi_cmdset_0002(struct map_info *, int);
@@ -443,6 +446,7 @@ struct mtd_info *cfi_cmdset_0002(struct map_info *map, int primary)
 	pr_debug("MTD %s(): write buffer size %d\n", __func__,
 			mtd->writebufsize);
 
+	mtd->panic_write = cfi_amdstd_panic_write;
 	mtd->reboot_notifier.notifier_call = cfi_amdstd_reboot;
 
 	if (cfi->cfi_mode==CFI_MODE_CFI){
@@ -1562,6 +1566,242 @@ static int cfi_amdstd_write_buffers(struct mtd_info *mtd, loff_t to, size_t len,
 	return 0;
 }
 
+/*
+ * Wait for the flash chip to become ready to write data
+ *
+ * This is only called during the panic_write() path. When panic_write()
+ * is called, the kernel is in the process of a panic, and will soon be
+ * dead. Therefore we don't take any locks, and attempt to get access
+ * to the chip as soon as possible.
+ */
+static int cfi_amdstd_panic_wait(struct map_info *map, struct flchip *chip,
+				 unsigned long adr)
+{
+	struct cfi_private *cfi = map->fldrv_priv;
+	int retries = 10;
+	int i;
+
+	/*
+	 * If the driver thinks the chip is idle, and no toggle bits
+	 * are changing, then the chip is actually idle for sure.
+	 */
+	if (chip->state == FL_READY && chip_ready(map, adr))
+		return 0;
+
+	/*
+	 * Try several times to reset the chip and then wait for it
+	 * to become idle. The upper limit of a few milliseconds of
+	 * delay isn't a big problem: the kernel is dying anyway. It
+	 * is more important to save the messages.
+	 */
+	while (retries > 0) {
+		const unsigned long timeo = (HZ / 1000) + 1;
+
+		/* send the reset command */
+		map_write(map, CMD(0xF0), chip->start);
+
+		/* wait for the chip to become ready */
+		for (i = 0; i < jiffies_to_usecs(timeo); i++) {
+			if (chip_ready(map, adr))
+				return 0;
+
+			udelay(1);
+		}
+	}
+
+	/* the chip never became ready */
+	return -EBUSY;
+}
+
+/*
+ * Write out one word of data to a single flash chip during a kernel panic
+ *
+ * This is only called during the panic_write() path. When panic_write()
+ * is called, the kernel is in the process of a panic, and will soon be
+ * dead. Therefore we don't take any locks, and attempt to get access
+ * to the chip as soon as possible.
+ *
+ * The implementation of this routine is intentionally similar to
+ * do_write_oneword(), in order to ease code maintenance.
+ */
+static int do_panic_write_oneword(struct map_info *map, struct flchip *chip,
+				  unsigned long adr, map_word datum)
+{
+	const unsigned long uWriteTimeout = (HZ / 1000) + 1;
+	struct cfi_private *cfi = map->fldrv_priv;
+	int retry_cnt = 0;
+	map_word oldd;
+	int ret = 0;
+	int i;
+
+	adr += chip->start;
+
+	ret = cfi_amdstd_panic_wait(map, chip, adr);
+	if (ret)
+		return ret;
+
+	pr_debug("MTD %s(): PANIC WRITE 0x%.8lx(0x%.8lx)\n",
+			__func__, adr, datum.x[0]);
+
+	/*
+	 * Check for a NOP for the case when the datum to write is already
+	 * present - it saves time and works around buggy chips that corrupt
+	 * data at other locations when 0xff is written to a location that
+	 * already contains 0xff.
+	 */
+	oldd = map_read(map, adr);
+	if (map_word_equal(map, oldd, datum)) {
+		pr_debug("MTD %s(): NOP\n", __func__);
+		goto op_done;
+	}
+
+	ENABLE_VPP(map);
+
+retry:
+	cfi_send_gen_cmd(0xAA, cfi->addr_unlock1, chip->start, map, cfi, cfi->device_type, NULL);
+	cfi_send_gen_cmd(0x55, cfi->addr_unlock2, chip->start, map, cfi, cfi->device_type, NULL);
+	cfi_send_gen_cmd(0xA0, cfi->addr_unlock1, chip->start, map, cfi, cfi->device_type, NULL);
+	map_write(map, datum, adr);
+
+	for (i = 0; i < jiffies_to_usecs(uWriteTimeout); i++) {
+		if (chip_ready(map, adr))
+			break;
+
+		udelay(1);
+	}
+
+	if (!chip_good(map, adr, datum)) {
+		/* reset on all failures. */
+		map_write(map, CMD(0xF0), chip->start);
+		/* FIXME - should have reset delay before continuing */
+
+		if (++retry_cnt <= MAX_WORD_RETRIES)
+			goto retry;
+
+		ret = -EIO;
+	}
+
+op_done:
+	DISABLE_VPP(map);
+	return ret;
+}
+
+/*
+ * Write out some data during a kernel panic
+ *
+ * This is used by the mtdoops driver to save the dying messages from a
+ * kernel which has panic'd.
+ *
+ * This routine ignores all of the locking used throughout the rest of the
+ * driver, in order to ensure that the data gets written out no matter what
+ * state this driver (and the flash chip itself) was in when the kernel crashed.
+ *
+ * The implementation of this routine is intentionally similar to
+ * cfi_amdstd_write_words(), in order to ease code maintenance.
+ */
+static int cfi_amdstd_panic_write(struct mtd_info *mtd, loff_t to, size_t len,
+				  size_t *retlen, const u_char *buf)
+{
+	struct map_info *map = mtd->priv;
+	struct cfi_private *cfi = map->fldrv_priv;
+	unsigned long ofs, chipstart;
+	int ret = 0;
+	int chipnum;
+
+	*retlen = 0;
+	if (!len)
+		return 0;
+
+	chipnum = to >> cfi->chipshift;
+	ofs = to - (chipnum << cfi->chipshift);
+	chipstart = cfi->chips[chipnum].start;
+
+	/* If it's not bus aligned, do the first byte write */
+	if (ofs & (map_bankwidth(map) - 1)) {
+		unsigned long bus_ofs = ofs & ~(map_bankwidth(map) - 1);
+		int i = ofs - bus_ofs;
+		int n = 0;
+		map_word tmp_buf;
+
+		ret = cfi_amdstd_panic_wait(map, &cfi->chips[chipnum], bus_ofs);
+		if (ret)
+			return ret;
+
+		/* Load 'tmp_buf' with old contents of flash */
+		tmp_buf = map_read(map, bus_ofs + chipstart);
+
+		/* Number of bytes to copy from buffer */
+		n = min_t(int, len, map_bankwidth(map) - i);
+
+		tmp_buf = map_word_load_partial(map, tmp_buf, buf, i, n);
+
+		ret = do_panic_write_oneword(map, &cfi->chips[chipnum],
+					     bus_ofs, tmp_buf);
+		if (ret)
+			return ret;
+
+		ofs += n;
+		buf += n;
+		(*retlen) += n;
+		len -= n;
+
+		if (ofs >> cfi->chipshift) {
+			chipnum++;
+			ofs = 0;
+			if (chipnum == cfi->numchips)
+				return 0;
+		}
+	}
+
+	/* We are now aligned, write as much as possible */
+	while (len >= map_bankwidth(map)) {
+		map_word datum;
+
+		datum = map_word_load(map, buf);
+
+		ret = do_panic_write_oneword(map, &cfi->chips[chipnum],
+					     ofs, datum);
+		if (ret)
+			return ret;
+
+		ofs += map_bankwidth(map);
+		buf += map_bankwidth(map);
+		(*retlen) += map_bankwidth(map);
+		len -= map_bankwidth(map);
+
+		if (ofs >> cfi->chipshift) {
+			chipnum++;
+			ofs = 0;
+			if (chipnum == cfi->numchips)
+				return 0;
+
+			chipstart = cfi->chips[chipnum].start;
+		}
+	}
+
+	/* Write the trailing bytes if any */
+	if (len & (map_bankwidth(map) - 1)) {
+		map_word tmp_buf;
+
+		ret = cfi_amdstd_panic_wait(map, &cfi->chips[chipnum], ofs);
+		if (ret)
+			return ret;
+
+		tmp_buf = map_read(map, ofs + chipstart);
+
+		tmp_buf = map_word_load_partial(map, tmp_buf, buf, 0, len);
+
+		ret = do_panic_write_oneword(map, &cfi->chips[chipnum],
+					     ofs, tmp_buf);
+		if (ret)
+			return ret;
+
+		(*retlen) += len;
+	}
+
+	return 0;
+}
+
 
 /*
  * Handle devices with one erase region, that only implement