mtd: nand: denali: allow to override revision number

Commit 271707b1 ("mtd: nand: denali: max_banks calculation
changed in revision 5.1") added a revision check to support the
new max_banks encoding.  Its git-log states "The encoding of
max_banks changed in Denali revision 5.1".

There are exceptional cases, for example, the revision register on
some UniPhier SoCs says the IP is 5.0 but the max_banks is encoded
in the new format.

This IP updates the resister specification from time to time (often
breaking the backward compatibility), but the revision number is not
incremented correctly.

The max_banks is not only the case that needs revision checking.
Let's allow to override an incorrect revision number.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/denali.c

@@ -419,17 +419,12 @@ static void find_valid_banks(struct denali_nand_info *denali)
 static void detect_max_banks(struct denali_nand_info *denali)
 {
 	uint32_t features = ioread32(denali->flash_reg + FEATURES);
-	/*
-	 * Read the revision register, so we can calculate the max_banks
-	 * properly: the encoding changed from rev 5.0 to 5.1
-	 */
-	u32 revision = MAKE_COMPARABLE_REVISION(
-				ioread32(denali->flash_reg + REVISION));
 
-	if (revision < REVISION_5_1)
-		denali->max_banks = 2 << (features & FEATURES__N_BANKS);
-	else
 	denali->max_banks = 1 << (features & FEATURES__N_BANKS);
+
+	/* the encoding changed from rev 5.0 to 5.1 */
+	if (denali->revision < 0x0501)
+		denali->max_banks <<= 1;
 }
 
 static uint16_t denali_nand_timing_set(struct denali_nand_info *denali)
@@ -1319,6 +1314,14 @@ static void denali_cmdfunc(struct mtd_info *mtd, unsigned int cmd, int col,
 /* Initialization code to bring the device up to a known good state */
 static void denali_hw_init(struct denali_nand_info *denali)
 {
+	/*
+	 * The REVISION register may not be reliable.  Platforms are allowed to
+	 * override it.
+	 */
+	if (!denali->revision)
+		denali->revision =
+				swab16(ioread32(denali->flash_reg + REVISION));
+
 	/*
 	 * tell driver how many bit controller will skip before
 	 * writing ECC code in OOB, this register may be already

drivers/mtd/nand/denali.h

@@ -179,8 +179,6 @@
 
 #define REVISION				0x370
 #define     REVISION__VALUE				0xffff
-#define MAKE_COMPARABLE_REVISION(x)		swab16((x) & REVISION__VALUE)
-#define REVISION_5_1				0x00000501
 
 #define ONFI_DEVICE_FEATURES			0x380
 #define     ONFI_DEVICE_FEATURES__VALUE			0x003f
@@ -343,6 +341,7 @@ struct denali_nand_info {
 	int devnum;	/* represent how many nands connected */
 	int bbtskipbytes;
 	int max_banks;
+	unsigned int revision;
 	unsigned int caps;
 };
 

drivers/mtd/nand/denali_dt.c

@@ -30,6 +30,7 @@ struct denali_dt {
 };
 
 struct denali_dt_data {
+	unsigned int revision;
 	unsigned int caps;
 };
 
@@ -60,8 +61,10 @@ static int denali_dt_probe(struct platform_device *pdev)
 	denali = &dt->denali;
 
 	data = of_device_get_match_data(&pdev->dev);
-	if (data)
+	if (data) {
+		denali->revision = data->revision;
 		denali->caps = data->caps;
+	}
 
 	denali->platform = DT;
 	denali->dev = &pdev->dev;