mmc: block: copy resp[] data on err for MMC_IOC_MULTI_CMD

MMC_IOC_CMD and MMC_IOC_MULTI_CMD ioctl() code currently bails on
any eMMC errors. However, in case there is any resp[] data, we
should attempt to copy resp[] back to user space. The user app
can then determine which command(s) failed in the MMC_IOC_MULTI_CMD
case AND/OR report better diagnostics in both cases.

Gwendal Grignou provided the idea and it was previously implemented
and tested on v3.18 ChromeOS kernel:
    https://chromium-review.googlesource.com/#/c/299956

Signed-off-by: Grant Grundler <grundler@chromium.org>
Reviewed-by: Hyung Taek Ryoo <hryoo@nvidia.com>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Tested-by: David Riley <davidriley@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/card/block.c

@@ -595,7 +595,7 @@ static int mmc_blk_ioctl_cmd(struct block_device *bdev,
 	struct mmc_blk_ioc_data *idata;
 	struct mmc_blk_data *md;
 	struct mmc_card *card;
-	int err;
+	int err = 0, ioc_err = 0;
 
 	idata = mmc_blk_ioctl_copy_from_user(ic_ptr);
 	if (IS_ERR(idata))
@@ -615,19 +615,18 @@ static int mmc_blk_ioctl_cmd(struct block_device *bdev,
 
 	mmc_get_card(card);
 
-	err = __mmc_blk_ioctl_cmd(card, md, idata);
+	ioc_err = __mmc_blk_ioctl_cmd(card, md, idata);
 
 	mmc_put_card(card);
 
-	if (!err)
-		err = mmc_blk_ioctl_copy_to_user(ic_ptr, idata);
+	err = mmc_blk_ioctl_copy_to_user(ic_ptr, idata);
 
 cmd_done:
 	mmc_blk_put(md);
 cmd_err:
 	kfree(idata->buf);
 	kfree(idata);
-	return err;
+	return ioc_err ? ioc_err : err;
 }
 
 static int mmc_blk_ioctl_multi_cmd(struct block_device *bdev,
@@ -637,7 +636,7 @@ static int mmc_blk_ioctl_multi_cmd(struct block_device *bdev,
 	struct mmc_ioc_cmd __user *cmds = user->cmds;
 	struct mmc_card *card;
 	struct mmc_blk_data *md;
-	int i, err = -EFAULT;
+	int i, err = 0, ioc_err = 0;
 	__u64 num_of_cmds;
 
 	if (copy_from_user(&num_of_cmds, &user->num_of_cmds,
@@ -672,22 +671,14 @@ static int mmc_blk_ioctl_multi_cmd(struct block_device *bdev,
 
 	mmc_get_card(card);
 
-	for (i = 0; i < num_of_cmds; i++) {
-		err = __mmc_blk_ioctl_cmd(card, md, idata[i]);
-		if (err) {
-			mmc_put_card(card);
-			goto cmd_done;
-		}
-	}
+	for (i = 0; i < num_of_cmds && !ioc_err; i++)
+		ioc_err = __mmc_blk_ioctl_cmd(card, md, idata[i]);
 
 	mmc_put_card(card);
 
 	/* copy to user if data and response */
-	for (i = 0; i < num_of_cmds; i++) {
+	for (i = 0; i < num_of_cmds && !err; i++)
 		err = mmc_blk_ioctl_copy_to_user(&cmds[i], idata[i]);
-		if (err)
-			break;
-	}
 
 cmd_done:
 	mmc_blk_put(md);
@@ -697,7 +688,7 @@ static int mmc_blk_ioctl_multi_cmd(struct block_device *bdev,
 		kfree(idata[i]);
 	}
 	kfree(idata);
-	return err;
+	return ioc_err ? ioc_err : err;
 }
 
 static int mmc_blk_ioctl(struct block_device *bdev, fmode_t mode,