mtd: nand: support ONFI timing mode retrieval for non-ONFI NANDs

Add an onfi_timing_mode_default field to nand_chip and nand_flash_dev in
order to support NAND timings definition for non-ONFI NAND.

NAND that support better timings mode than the default one have to define
a new entry in the nand_ids table.

The default timing mode should be deduced from timings description from
the datasheet and the ONFI specification
(www.onfi.org/~/media/ONFI/specs/onfi_3_1_spec.pdf, chapter 4.15
"Timing Parameters").
You should choose the closest mode that fit the timings requirements of
your NAND chip.
Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/nand_base.c

@@ -3594,6 +3594,8 @@ static bool find_full_id_nand(struct mtd_info *mtd, struct nand_chip *chip,
 		chip->options |= type->options;
 		chip->ecc_strength_ds = NAND_ECC_STRENGTH(type);
 		chip->ecc_step_ds = NAND_ECC_STEP(type);
+		chip->onfi_timing_mode_default =
+					type->onfi_timing_mode_default;
 
 		*busw = type->options & NAND_BUSWIDTH_16;
 

include/linux/mtd/nand.h

@@ -587,6 +587,11 @@ struct nand_buffers {
  * @ecc_step_ds:	[INTERN] ECC step required by the @ecc_strength_ds,
  *                      also from the datasheet. It is the recommended ECC step
  *			size, if known; if unknown, set to zero.
+ * @onfi_timing_mode_default: [INTERN] default ONFI timing mode. This field is
+ *			      either deduced from the datasheet if the NAND
+ *			      chip is not ONFI compliant or set to 0 if it is
+ *			      (an ONFI chip is always configured in mode 0
+ *			      after a NAND reset)
  * @numchips:		[INTERN] number of physical chips
  * @chipsize:		[INTERN] the size of one chip for multichip arrays
  * @pagemask:		[INTERN] page number mask = number of (pages / chip) - 1
@@ -671,6 +676,7 @@ struct nand_chip {
 	uint8_t bits_per_cell;
 	uint16_t ecc_strength_ds;
 	uint16_t ecc_step_ds;
+	int onfi_timing_mode_default;
 	int badblockpos;
 	int badblockbits;
 
@@ -773,6 +779,10 @@ struct nand_chip {
  *               @ecc_step_ds in nand_chip{}, also from the datasheet.
  *               For example, the "4bit ECC for each 512Byte" can be set with
  *               NAND_ECC_INFO(4, 512).
+ * @onfi_timing_mode_default: the default ONFI timing mode entered after a NAND
+ *			      reset. Should be deduced from timings described
+ *			      in the datasheet.
+ *
  */
 struct nand_flash_dev {
 	char *name;
@@ -793,6 +803,7 @@ struct nand_flash_dev {
 		uint16_t strength_ds;
 		uint16_t step_ds;
 	} ecc;
+	int onfi_timing_mode_default;
 };
 
 /**