mtd: nand: denali: avoid hard-coding ECC step, strength, bytes

This driver was originally written for the Intel MRST platform with
several platform-specific parameters hard-coded.

Currently, the ECC settings are hard-coded as follows:

  #define ECC_SECTOR_SIZE 512
  #define ECC_8BITS       14
  #define ECC_15BITS      26

Therefore, the driver can only support two cases.
 - ecc.size = 512, ecc.strength = 8    --> ecc.bytes = 14
 - ecc.size = 512, ecc.strength = 15   --> ecc.bytes = 26

However, these are actually customizable parameters, for example,
UniPhier platform supports the following:

 - ecc.size = 1024, ecc.strength = 8   --> ecc.bytes = 14
 - ecc.size = 1024, ecc.strength = 16  --> ecc.bytes = 28
 - ecc.size = 1024, ecc.strength = 24  --> ecc.bytes = 42

So, we need to handle the ECC parameters in a more generic manner.
Fortunately, the Denali User's Guide explains how to calculate the
ecc.bytes.  The formula is:

  ecc.bytes = 2 * CEIL(13 * ecc.strength / 16)  (for ecc.size = 512)
  ecc.bytes = 2 * CEIL(14 * ecc.strength / 16)  (for ecc.size = 1024)

For DT platforms, it would be reasonable to allow DT to specify ECC
strength by either "nand-ecc-strength" or "nand-ecc-maximize".  If
none of them is specified, the driver will try to meet the chip's ECC
requirement.

For PCI platforms, the max ECC strength is used to keep the original
behavior.

Newer versions of this IP need ecc.size and ecc.steps explicitly
set up via the following registers:
  CFG_DATA_BLOCK_SIZE       (0x6b0)
  CFG_LAST_DATA_BLOCK_SIZE  (0x6c0)
  CFG_NUM_DATA_BLOCKS       (0x6d0)

For older IP versions, write accesses to these registers are just
ignored.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/mtd/denali-nand.txt b/Documentation/devicetree/bindings/mtd/denali-nand.txt
index e593bbeb2115..b7742a7363ea 100644
--- a/Documentation/devicetree/bindings/mtd/denali-nand.txt
+++ b/Documentation/devicetree/bindings/mtd/denali-nand.txt
@@ -7,6 +7,13 @@ Required properties:
   - reg-names: Should contain the reg names "nand_data" and "denali_reg"
   - interrupts : The interrupt number.
 
+Optional properties:
+  - nand-ecc-step-size: see nand.txt for details.  If present, the value must be
+      512        for "altr,socfpga-denali-nand"
+  - nand-ecc-strength: see nand.txt for details.  Valid values are:
+      8, 15      for "altr,socfpga-denali-nand"
+  - nand-ecc-maximize: see nand.txt for details
+
 The device tree may optionally contain sub-nodes describing partitions of the
 address space. See partition.txt for more detail.