[PATCH] mtd: rawnand: nand_base: Handle algorithm selection

[Rafał Miłecki]

On 26.01.2023 02:14, William Zhang wrote:
> On 01/21/2023 03:43 PM, Linus Walleij wrote:
>> For BRCMNAND with 1-bit BCH ECC (BCH-1) such as used on the
>> D-Link DIR-885L and DIR-890L routers, we need to explicitly
>> select the ECC like this in the device tree:
>>
>>    nand-ecc-algo = "bch";
>>    nand-ecc-strength = <1>;
>>    nand-ecc-step-size = <512>;
>>
>> This is handled by the Linux kernel but U-Boot core does
>> not respect this. Fix it up by parsing the algorithm and
>> preserve the behaviour using this property to select
>> software BCH as far as possible.
> 
> For 1 bit HW ECC, the BRCMNAND driver only uses HAMMING ECC.  The brcmnand_setup_dev function should take care of it with just these two properties in the device tress without any code changes:
>      nand-ecc-strength = <1>;
>      nand-ecc-step-size = <512>;
> unless these D-Link device has always been using software BCH-1 and wants to continue to use software BCH-1.

Please check
arch/arm/boot/dts/bcm5301x-nand-cs0-bch1.dtsi
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/bcm5301x-nand-cs0-bch1.dtsi

It's included by
arch/arm/boot/dts/bcm47094-dlink-dir-885l.dts
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/bcm47094-dlink-dir-885l.dts

I can confirm D-Link decided to use BCH-1 for some of its devices. I
didn't expect it neither and that required fixing up brcmnand driver in
Linux actually.


> BTW,  I didn't see this change from master branch of linux nand base driver. The "nand-ecc-algo" is only used by the ecc engine code(ecc.c) but this code is not in the u-boot obviously. Were you porting this from a different version of linux nand driver?

My original proposal for brcmnand looked like this:
[PATCH 3/3] mtd: brcmnand: respect ECC algorithm set by NAND subsystem
https://lore.kernel.org/lkml/1461324197-1333-3-git-send-email-zajec5@gmail.com/

It was reworked by Brian to a more backward compatible solution that got
accepted:
[PATCH] mtd: brcmnand: respect ECC algorithm set by the NAND subsystem
https://lore.kernel.org/lkml/20160426055355.GA25981@localhost/
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=666b65683dad9aa90efaa4aad24ef3710101e3aa