scsi: core: Simplify scsi_cdl_check_cmd()

Reading the 800+ pages of SPC often leads to a brain shutdown and to less
than ideal code... This resulted in the checks of the rwcdlp and cdlp
fields in scsi_cdl_check_cmd() to have identical if-else branches.

Replace this with a comment describing the cases we are interested in and
replace the if-else code block with a simple test of the cdlp field that is
used as the function return value.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Closes: https://lore.kernel.org/r/202306221657.BJHEADkz-lkp@intel.com/
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230623073057.816199-1-dlemoal@kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index c4bf99a842f366d75c4b54c88dd49225c492af9a..d0911bc28663a8142d0fb0ae69dbad1348efa385 100644 (file)
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -586,31 +586,22 @@ static bool scsi_cdl_check_cmd(struct scsi_device *sdev, u8 opcode, u16 sa,
        if ((buf[1] & 0x03) != 0x03)
                return false;
 
-       /* See SPC-6, one command format of REPORT SUPPORTED OPERATION CODES */
+       /*
+        * See SPC-6, One_command parameter data format for
+        * REPORT SUPPORTED OPERATION CODES. We have the following cases
+        * depending on rwcdlp (buf[0] & 0x01) value:
+        *  - rwcdlp == 0: then cdlp indicates support for the A mode page when
+        *                 it is equal to 1 and for the B mode page when it is
+        *                 equal to 2.
+        *  - rwcdlp == 1: then cdlp indicates support for the T2A mode page
+        *                 when it is equal to 1 and for the T2B mode page when
+        *                 it is equal to 2.
+        * Overall, to detect support for command duration limits, we only need
+        * to check that cdlp is 1 or 2.
+        */
        cdlp = (buf[1] & 0x18) >> 3;
-       if (buf[0] & 0x01) {
-               /* rwcdlp == 1 */
-               switch (cdlp) {
-               case 0x01:
-                       /* T2A page */
-                       return true;
-               case 0x02:
-                       /* T2B page */
-                       return true;
-               }
-       } else {
-               /* rwcdlp == 0 */
-               switch (cdlp) {
-               case 0x01:
-                       /* A page */
-                       return true;
-               case 0x02:
-                       /* B page */
-                       return true;
-               }
-       }
 
-       return false;
+       return cdlp == 0x01 || cdlp == 0x02;
 }
 
 /**