[PATCH 1/3] cdrom: Reset sector_size back it is not 2048.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

In v2.4.0-test2pre2 mmc_ioctl_cdrom_read_data() was extended by issuing
a MODE_SELECT opcode to change the sector size and READ_10 to perform
the actual read if the READ_CD opcode is not support.
The sector size is never changed back to the previous value of 2048
bytes which is however denoted by the comment for version 3.09 of the
cdrom.c file.

Use cdrom_switch_blocksize() to change the sector size only if the
requested size deviates from 2048. Change it back to 2048 after the read
operation if a change was mode.

Link: https://lkml.kernel.org/r/20201204164803.ovwurzs3257em2rp@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/cdrom/cdrom.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 0c271b9e3c5b7..8f0e52a714938 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -2996,13 +2996,15 @@ static noinline int mmc_ioctl_cdrom_read_data(struct cdrom_device_info *cdi,
 		 * SCSI-II devices are not required to support
 		 * READ_CD, so let's try switching block size
 		 */
-		/* FIXME: switch back again... */
-		ret = cdrom_switch_blocksize(cdi, blocksize);
-		if (ret)
-			goto out;
+		if (blocksize != CD_FRAMESIZE) {
+			ret = cdrom_switch_blocksize(cdi, blocksize);
+			if (ret)
+				goto out;
+		}
 		cgc->sshdr = NULL;
 		ret = cdrom_read_cd(cdi, cgc, lba, blocksize, 1);
-		ret |= cdrom_switch_blocksize(cdi, blocksize);
+		if (blocksize != CD_FRAMESIZE)
+			ret |= cdrom_switch_blocksize(cdi, CD_FRAMESIZE);
 	}
 	if (!ret && copy_to_user(arg, cgc->buffer, blocksize))
 		ret = -EFAULT;
-- 
2.29.2