Re: [PATCH 10/10] mtd: spi-nor: aspeed: optimize read mode

Marek Vasut
2017-04-14T22:26:15Z

On 04/15/2017 12:11 AM, Benjamin Herrenschmidt wrote:
> On Fri, 2017-04-14 at 23:51 +0200, Marek Vasut wrote:
>> On 04/14/2017 11:40 PM, Benjamin Herrenschmidt wrote:
>>>
>>> Strong disagreement here :-)
>>>
>>> DT is not *strictly* HW properties. Never was despite what some
>>> fanatics around might say :-) Its also platform properties and can
>>> include policies.
>>
>> /me grabs popcorn ... :-)
>
> Be my guest ! I only invented the bloody thing in the first place after
> all ;-) (Well, the FDT format rather, and its use in Linux, the DT
> itself dates back from Open Firmware).

:-)

>>> We put things like UART speeds in there, MAC addresses, etc...
>>
>> UART speeds or UART max/allowed speeds ? That's basically HW property
>> since flaky HW might not allow all sorts of UART speed options. MAC
>> address is a HW property.
>
> Both. The point is that there is no hard lines. Every time people come
> up with hard lines, we end up with inflexible horror shows that fail to
> solve practical issues on the field.

True

> There is no good reason to forbid passing such a simple policy argument
> that way. None. Other than ideological that is.
>
>>> it makes
>>> sense to put calibration info and in this case, request to perform
>>> SW
>>> calibration.
>>
>> That's a hard question and I don't have the right answer to this.
>
> I do, and it's fine :-)
>
>>> Module parameters are crap. They are a major pain to use, they are
>>> in
>>> practice only good for tweaking/experimenting.
>>
>> That's correct, but then turning the calibration off would probably
>> be only used in such experimental setups or during HW bringup (if at
>> all).
>> Based on the discussion thus far, my impression is that thepreferred
>> and mostly used default is calibration enabled.
>
> Probably yes. So we could reverse the problem and say that we have
> the calibration enabled by default, and an optional device-tree
> property to force a fixed speed.

That sounds like a good option, yes. And if it's just forcing fixed
speed, that's awesome, but I think there are more values that might need
to be passed ... I think that's what Cedric can answer.

> That becomes akin to what we do with Ethernet PHYs for example :)

Even better, I recall seeing some speed DT props in the SPI binding
docs, so we already have those in place.

> Cheers,
> Ben.
>
>>
>>

--
Best regards,
Marek Vasut