omap_gpmc: add support for hw assisted BCH8

The kernel states:

---8<---
The OMAP3 GPMC hardware BCH engine computes remainder polynomials, it does not
provide automatic error location and correction: this step is implemented using
the BCH library.
--->8---

And we do so in u-boot.

This implementation uses the same layout for BCH8 but it is fix. The current
provided layout does only work with 64 Byte OOB.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
Cc: Tom Rini <trini@ti.com>
Cc: Ilya Yanok <ilya.yanok@cogentembedded.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Mansoor Ahamed <mansoor.ahamed@ti.com>
Cc: Thomas Weber <thomas.weber.linux@googlemail.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/doc/README.omap3 b/doc/README.omap3
index 0a37de0..1fbe79d 100644
--- a/doc/README.omap3
+++ b/doc/README.omap3
@@ -145,6 +145,34 @@ int omap3_dma_wait_for_transfer(uint32_t chan)
 int omap3_dma_get_revision(uint32_t *minor, uint32_t *major)
 	Read silicon Revision of the DMA module
 
+NAND
+====
+
+There are some OMAP3 devices out there with NAND attached. Due to the fact that
+OMAP3 ROM code can only handle 1-bit hamming ECC for accessing first page
+(place where SPL lives) we require this setup for u-boot at least when reading
+the second progam within SPL.  A lot of newer NAND chips however require more
+than 1-bit ECC for the pages, some can live with 1-bit for the first page. To
+handle this we can switch to another ECC algorithm after reading the payload
+within SPL.
+
+BCH8
+----
+
+To enable hardware assisted BCH8 (8-bit BCH [Bose, Chaudhuri, Hocquenghem]) on
+OMAP3 devices we can use the BCH library in lib/bch.c. To do so add CONFIG_BCH
+to enable the library and CONFIG_NAND_OMAP_BCH8 to to enable hardware assisted
+syndrom generation to your board config.
+The NAND OOB layout is the same as in linux kernel, if the linux kernel BCH8
+implementation for OMAP3 works for you so the u-boot version should also.
+When you require the SPL to read with BCH8 there are two more configs to
+change:
+
+ * CONFIG_SYS_NAND_ECCPOS (must be the same as .eccpos in
+   GPMC_NAND_HW_BCH8_ECC_LAYOUT defined in
+   arch/arm/include/asm/arch-omap3/omap_gpmc.h)
+ * CONFIG_SYS_NAND_ECCSIZE must be 512
+ * CONFIG_SYS_NAND_ECCBYTES must be 13 for this BCH8 setup
 
 Acknowledgements
 ================