[Letux-kernel] ECC

H. Nikolaus Schaller hns at goldelico.com
Sun Mar 19 18:43:18 CET 2017


Hi Marek,

> Am 18.03.2017 um 08:54 schrieb Belisko Marek <marek.belisko at gmail.com>:
> 
> Hi Nikolaus,
> 
> On Sat, Mar 18, 2017 at 8:44 AM, Belisko Marek <marek.belisko at gmail.com> wrote:
>> Hi Nikolaus,
>>>>> 
>>>>> There is only one remaining issue with our latest U-Boot and Kernel: the NAND
>>>>> ECC mode does not match between U-Boot and Kernel (OneNAND has no choice for that).
>>>> Probably ECC options are different between u-boot and kernel (dts)?
>>> 
>>> Yes, they disagree.
>>> 
>>> The question is how to make them agree...
>>> 
>>> AFAIR, MLO must have some specific ECC enabled while the other partitions are a
>>> little more configurable.
>>> 
>>> The main problem seems to be that the kernel does not have ECC specification for
>>> individual partitions but only for the full chip. This means there is no real
>>> flexibility if we want to load MLO from NAND.
>>> 
>>> Maybe we can look into the BeagleBoard setup?
>>> 
>>> @Marek: if you have a little time, could you help to research the settings?
>> Yes I'll look on that and get back with findings.
> OK in kernel dts we have bch8 ecc scheme selected and it's sw
> detection. AFAIK only am33xx have elm module which is used for
> HW ecc. And u-boot is using (in omap3_beagle.h inherited)
> OMAP_ECC_HAM1_CODE_HW so we should somehow align them.
> I don't have board by hand now so it's not verified but I think this
> is a problem. There is an u-boot command to switch ecc schme so I'll
> try (probably on Sunday) to test if we can access u-boot env from
> linux.

I have now looked up the DT of the BeagleBoard (not XM) which has a very similar
NAND chip. They seem to use "ham1" as the ECC mode in the device tree:

http://lxr.free-electrons.com/source/arch/arm/boot/dts/omap3-beagle.dts#L392

Unfortunately, I can't read the fw_printenv either:


And the device tree is strange. Here is the source patch:

diff --git a/arch/arm/boot/dts/omap3-gta04.dtsi b/arch/arm/boot/dts/omap3-gta04.dtsi
index 907abcf..ad6ac7d 100644
--- a/arch/arm/boot/dts/omap3-gta04.dtsi
+++ b/arch/arm/boot/dts/omap3-gta04.dtsi
@@ -636,7 +636,7 @@
                interrupts = <0 IRQ_TYPE_NONE>, /* fifoevent */
                             <1 IRQ_TYPE_NONE>; /* termcount */
                nand-bus-width = <16>;
-               ti,nand-ecc-opt = "bch8";
+               ti,nand-ecc-opt = "ham1";
 
                gpmc,sync-clk-ps = <0>;
                gpmc,cs-on-ns = <0>;

And what I get...

root at letux:~# /usr/bin/fdtdump /sys/firmware/fdt |fgrep ecc
                ti,nand-ecc-opt = "sw";
root at letux:~# 

Strange. Does U-Boot or the kernel overwrite this setting?

BR,
Nikolaus



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