ARM: OMAP2+: cleaned-up DT support of various ECC schemes

OMAP NAND driver support multiple ECC scheme, which can used in different
flavours, depending on in-build Hardware engines present on SoC.

This patch updates following in DT bindings related to sectionion of ecc-schemes
- ti,elm-id: replaces elm_id (maintains backward compatibility)
- ti,nand-ecc-opts: selection of h/w or s/w implementation of an ecc-scheme
	depends on ti,elm-id. (supported values ham1, bch4, and bch8)
- maintain backward compatibility to deprecated DT bindings (sw, hw, hw-romcode)

Below table shows different flavours of ecc-schemes supported by OMAP devices
+---------------------------------------+---------------+---------------+
| ECC scheme                            |ECC calculation|Error detection|
+---------------------------------------+---------------+---------------+
|OMAP_ECC_HAM1_CODE_HW                  |H/W (GPMC)     |S/W            |
+---------------------------------------+---------------+---------------+
|OMAP_ECC_BCH8_CODE_HW_DETECTION_SW     |H/W (GPMC)     |S/W            |
|(requires CONFIG_MTD_NAND_ECC_BCH)     |               |               |
+---------------------------------------+---------------+---------------+
|OMAP_ECC_BCH8_CODE_HW                  |H/W (GPMC)     |H/W (ELM)      |
|(requires CONFIG_MTD_NAND_OMAP_BCH &&  |               |               |
| ti,elm-id in DT)                      |               |               |
+---------------------------------------+---------------+---------------+

To optimize footprint of omap2-nand driver, selection of some ECC schemes
also require enabling following Kconfigs, in addition to setting appropriate
DT bindings
- Kconfig:CONFIG_MTD_NAND_ECC_BCH        error detection done in software
- Kconfig:CONFIG_MTD_NAND_OMAP_BCH       error detection done by h/w engine

Signed-off-by: Pekon Gupta <pekon@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
index df338cb5059c..bfe07e152738 100644
--- a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
+++ b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
@@ -36,8 +36,12 @@ Optional properties:
                 "prefetch-dma"          Prefetch enabled sDMA mode
                 "prefetch-irq"          Prefetch enabled irq mode
 
- - elm_id:      Specifies elm device node. This is required to support BCH
-                error correction using ELM module.
+ - elm_id:      <deprecated> use "ti,elm-id" instead
+ - ti,elm-id:   Specifies phandle of the ELM devicetree node.
+                ELM is an on-chip hardware engine on TI SoC which is used for
+                locating ECC errors for BCHx algorithms. SoC devices which have
+                ELM hardware engines should specify this device node in .dtsi
+                Using ELM for ECC error correction frees some CPU cycles.
 
 For inline partiton table parsing (optional):