Re: [PATCH] mtd: brcmnand: set initial ECC params based on info from HW

[Florian Fainelli <f.fainelli@gmail.com>]

On 01/02/16 11:02, Brian Norris wrote:
> On Mon, Feb 01, 2016 at 10:09:28AM -0800, Florian Fainelli wrote:
>> On 01/02/16 09:53, Brian Norris wrote:
>>> Anyway, if we are really making the DT properties optional, we'd need to
>>> modify Documentation/devicetree/bindings/mtd/brcm,brcmnand.txt to
>>> reflect this.
>>
>> The Marvell PXA3XX NAND controller has a "marvell,nand-keep-config"
>> which seems to be in par with what Rafal is after here, maybe it would
>> be worth standardizing/mimicing that kind of property for the brcmnand
>> driver?
> 
> Maybe. Honestly, it's not that clear to me what the pxa3xx-nand binding
> means. But if we make that clear, that could be a possibility.

I would argue that if you were down the road of looking at the
bootloader defaults to figure out why things did not work, it's not that
much of a stretch to put the correct information in Device Tree, leading
to predictable results, so ...

> 
> (Side note: this isn't too far from what we did the Broadcom STB BSP
> previously, except that we wouldn't use device tree. We attempted a
> heuristic to detect whether the bootloader had initialized the flash
> controller properly... I didn't want to maintain that crazy logic
> upstream though. A DT flag to enable that behavior might be OK.)

Yes, I remember that part of the code, very much happy not to see it in
any upstream tree TBH.

> 
>>>> Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
>>>> ---
>>>> It took me hours to figure out how to setup NAND on my D-Link DIR-885L.
>>>> This should be very helpful for ppl adding new devices support.
>>>
>>> What if we just print out the hardware defaults when we bail out due to
>>> missing ECC DT properties? Then developers can choose to set up their DT
>>> with these properties, if those are actually proven correct. Would that
>>> save you the hours of setup you mention?
>>>
>>> Another option: maybe a commandline boot flag?
>>
>> One could argue that the bootloader is patf of the platform, and so, if
>> the bootloader is known to provide good defaults, then a DT property
>> could be appropriate. The commandline boot flag just sounds a little
>> impractical, in case you have more than one NAND controller, but how
>> common is that?
> 
> Not sure if you mean multiple *controller* or multiple *flash*. The
> former is much less common than the latter, but neither is very common
> AFAIK.

Multiple controllers, having multiple chips on a single controller is
indeed not that uncommon.

Thanks
-- 
Florian