mtd: rawnand: Add a helper for calculating a page index

For LUN crossing boundaries, it is handy to know what is the index of
the last page in a LUN. This helper will soon be reused. At the same
time I rename page_per_lun to ppl in the calling function to clarify the
lines.

Cc: stable@vger.kernel.org # v6.7
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240223115545.354541-3-miquel.raynal@bootlin.com

Author: miquelraynal

drivers/mtd/nand/raw/nand_base.c

@@ -1211,19 +1211,25 @@ static int nand_lp_exec_read_page_op(struct nand_chip *chip, unsigned int page,
 	return nand_exec_op(chip, &op);
 }
 
+static unsigned int rawnand_last_page_of_lun(unsigned int pages_per_lun, unsigned int lun)
+{
+	/* lun is expected to be very small */
+	return (lun * pages_per_lun) + pages_per_lun - 1;
+}
+
 static void rawnand_cap_cont_reads(struct nand_chip *chip)
 {
 	struct nand_memory_organization *memorg;
-	unsigned int pages_per_lun, first_lun, last_lun;
+	unsigned int ppl, first_lun, last_lun;
 
 	memorg = nanddev_get_memorg(&chip->base);
-	pages_per_lun = memorg->pages_per_eraseblock * memorg->eraseblocks_per_lun;
-	first_lun = chip->cont_read.first_page / pages_per_lun;
-	last_lun = chip->cont_read.last_page / pages_per_lun;
+	ppl = memorg->pages_per_eraseblock * memorg->eraseblocks_per_lun;
+	first_lun = chip->cont_read.first_page / ppl;
+	last_lun = chip->cont_read.last_page / ppl;
 
 	/* Prevent sequential cache reads across LUN boundaries */
 	if (first_lun != last_lun)
-		chip->cont_read.pause_page = first_lun * pages_per_lun + pages_per_lun - 1;
+		chip->cont_read.pause_page = rawnand_last_page_of_lun(ppl, first_lun);
 	else
 		chip->cont_read.pause_page = chip->cont_read.last_page;
 }