mtd: docg3 add protection against concurrency

As docg3 is intolerant against reentrancy, especially
because of its weird register access (ie. a register read is
performed by a first register write), each access to the
docg3 IO space must be locked.

Lock the IO space with a mutex, shared by all chips on the
same cascade, as they all share the same IO space.

Signed-off-by: Robert Jarzmik <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/devices/docg3.c

···
 	ops->retlen = 0;
 	ret = 0;
 	skip = from % DOC_LAYOUT_PAGE_SIZE;
+	mutex_lock(&docg3->cascade->lock);
 	while (!ret && (len > 0 || ooblen > 0)) {
 		calc_block_sector(from - skip, &block0, &block1, &page, &ofs,
 			docg3->reliable);
···
 		nboob = min_t(size_t, ooblen, (size_t)DOC_LAYOUT_OOB_SIZE);
 		ret = doc_read_page_prepare(docg3, block0, block1, page, ofs);
 		if (ret < 0)
-			goto err;
+			goto out;
 		ret = doc_read_page_ecc_init(docg3, DOC_ECC_BCH_TOTAL_BYTES);
 		if (ret < 0)
 			goto err_in_read;
···
 		skip = 0;
 	}
 
+out:
+	mutex_unlock(&docg3->cascade->lock);
 	return ret;
 err_in_read:
 	doc_read_page_finish(docg3);
-err:
-	return ret;
+	goto out;
 }
 
 /**
···
 	int block0, block1, page, ret, ofs = 0;
 
 	doc_dbg("doc_erase(from=%lld, len=%lld\n", info->addr, info->len);
-	doc_set_device_id(docg3, docg3->device_id);
 
 	info->state = MTD_ERASE_PENDING;
 	calc_block_sector(info->addr + info->len, &block0, &block1, &page,
···
 	ret = 0;
 	calc_block_sector(info->addr, &block0, &block1, &page, &ofs,
 			  docg3->reliable);
+	mutex_lock(&docg3->cascade->lock);
+	doc_set_device_id(docg3, docg3->device_id);
 	doc_set_reliable_mode(docg3);
 	for (len = info->len; !ret && len > 0; len -= mtd->erasesize) {
 		info->state = MTD_ERASING;
···
 		block0 += 2;
 		block1 += 2;
 	}
+	mutex_unlock(&docg3->cascade->lock);
 
 	if (ret)
 		goto reset_err;
···
 			 struct mtd_oob_ops *ops)
 {
 	struct docg3 *docg3 = mtd->priv;
-	int block0, block1, page, ret, pofs = 0, autoecc, oobdelta;
+	int ret, autoecc, oobdelta;
 	u8 *oobbuf = ops->oobbuf;
 	u8 *buf = ops->datbuf;
 	size_t len, ooblen;
···
 	if (autoecc < 0)
 		return autoecc;
 
+	mutex_lock(&docg3->cascade->lock);
 	while (!ret && len > 0) {
 		memset(oob, 0, sizeof(oob));
 		if (ofs == docg3->oob_write_ofs)
···
 		}
 		ops->retlen += DOC_LAYOUT_PAGE_SIZE;
 	}
-err:
+
 	doc_set_device_id(docg3, 0);
+	mutex_unlock(&docg3->cascade->lock);
 	return ret;
 }
 
···
 	struct docg3 *docg3 = sysfs_dev2docg3(dev, attr);
 	int dps0;
 
+	mutex_lock(&docg3->cascade->lock);
 	doc_set_device_id(docg3, docg3->device_id);
 	dps0 = doc_register_readb(docg3, DOC_DPS0_STATUS);
 	doc_set_device_id(docg3, 0);
+	mutex_unlock(&docg3->cascade->lock);
 
 	return sprintf(buf, "%d\n", !(dps0 & DOC_DPS_KEY_OK));
 }
···
 	struct docg3 *docg3 = sysfs_dev2docg3(dev, attr);
 	int dps1;
 
+	mutex_lock(&docg3->cascade->lock);
 	doc_set_device_id(docg3, docg3->device_id);
 	dps1 = doc_register_readb(docg3, DOC_DPS1_STATUS);
 	doc_set_device_id(docg3, 0);
+	mutex_unlock(&docg3->cascade->lock);
 
 	return sprintf(buf, "%d\n", !(dps1 & DOC_DPS_KEY_OK));
 }
···
 	if (count != DOC_LAYOUT_DPS_KEY_LENGTH)
 		return -EINVAL;
 
+	mutex_lock(&docg3->cascade->lock);
 	doc_set_device_id(docg3, docg3->device_id);
 	for (i = 0; i < DOC_LAYOUT_DPS_KEY_LENGTH; i++)
 		doc_writeb(docg3, buf[i], DOC_DPS0_KEY);
 	doc_set_device_id(docg3, 0);
+	mutex_unlock(&docg3->cascade->lock);
 	return count;
 }
 
···
 	if (count != DOC_LAYOUT_DPS_KEY_LENGTH)
 		return -EINVAL;
 
+	mutex_lock(&docg3->cascade->lock);
 	doc_set_device_id(docg3, docg3->device_id);
 	for (i = 0; i < DOC_LAYOUT_DPS_KEY_LENGTH; i++)
 		doc_writeb(docg3, buf[i], DOC_DPS1_KEY);
 	doc_set_device_id(docg3, 0);
+	mutex_unlock(&docg3->cascade->lock);
 	return count;
 }
 
···
 	struct docg3 *docg3 = (struct docg3 *)s->private;
 
 	int pos = 0;
-	u8 fctrl = doc_register_readb(docg3, DOC_FLASHCONTROL);
+	u8 fctrl;
+
+	mutex_lock(&docg3->cascade->lock);
+	fctrl = doc_register_readb(docg3, DOC_FLASHCONTROL);
+	mutex_unlock(&docg3->cascade->lock);
 
 	pos += seq_printf(s,
 		 "FlashControl : 0x%02x (%s,CE# %s,%s,%s,flash %s)\n",
···
 {
 	struct docg3 *docg3 = (struct docg3 *)s->private;
 
-	int pos = 0;
-	int pctrl = doc_register_readb(docg3, DOC_ASICMODE);
-	int mode = pctrl & 0x03;
+	int pos = 0, pctrl, mode;
+
+	mutex_lock(&docg3->cascade->lock);
+	pctrl = doc_register_readb(docg3, DOC_ASICMODE);
+	mode = pctrl & 0x03;
+	mutex_unlock(&docg3->cascade->lock);
 
 	pos += seq_printf(s,
 			 "%04x : RAM_WE=%d,RSTIN_RESET=%d,BDETCT_RESET=%d,WRITE_ENABLE=%d,POWERDOWN=%d,MODE=%d%d (",
···
 {
 	struct docg3 *docg3 = (struct docg3 *)s->private;
 	int pos = 0;
-	int id = doc_register_readb(docg3, DOC_DEVICESELECT);
+	int id;
+
+	mutex_lock(&docg3->cascade->lock);
+	id = doc_register_readb(docg3, DOC_DEVICESELECT);
+	mutex_unlock(&docg3->cascade->lock);
 
 	pos += seq_printf(s, "DeviceId = %d\n", id);
 	return pos;
···
 	int pos = 0;
 	int protect, dps0, dps0_low, dps0_high, dps1, dps1_low, dps1_high;
 
+	mutex_lock(&docg3->cascade->lock);
 	protect = doc_register_readb(docg3, DOC_PROTECTION);
 	dps0 = doc_register_readb(docg3, DOC_DPS0_STATUS);
 	dps0_low = doc_register_readw(docg3, DOC_DPS0_ADDRLOW);
···
 	dps1 = doc_register_readb(docg3, DOC_DPS1_STATUS);
 	dps1_low = doc_register_readw(docg3, DOC_DPS1_ADDRLOW);
 	dps1_high = doc_register_readw(docg3, DOC_DPS1_ADDRHIGH);
+	mutex_unlock(&docg3->cascade->lock);
 
 	pos += seq_printf(s, "Protection = 0x%02x (",
 			 protect);
···
 	if (!cascade)
 		goto nomem1;
 	cascade->base = base;
+	mutex_init(&cascade->lock);
 	cascade->bch = init_bch(DOC_ECC_BCH_M, DOC_ECC_BCH_T,
 			     DOC_ECC_BCH_PRIMPOLY);
 	if (!cascade->bch)

drivers/mtd/devices/docg3.h

···
  * @floors: floors (ie. one physical docg3 chip is one floor)
  * @base: IO space to access all chips in the cascade
  * @bch: the BCH correcting control structure
+ * @lock: lock to protect docg3 IO space from concurrent accesses
  */
 struct docg3_cascade {
 	struct mtd_info *floors[DOC_MAX_NBFLOORS];
 	void __iomem *base;
 	struct bch_control *bch;
+	struct mutex lock;
 };
 
 /**