physmap_of and partitions (mtd concat support)

[Grant Likely]

On Tue, Mar 24, 2009 at 9:39 AM, Stefan Roese <sr at denx.de> wrote:
> On Tuesday 24 March 2009, Grant Likely wrote:
>> >> Sounds to me like a physmap_of driver bug.  I don't think there is any
>> >> advantage in changing the partition syntax since concatenated flash
>> >> will always be used as a single device.  It doesn't make any sense to
>> >> try and span partitions over two nodes.
>> >
>> > Yes, I would really love to make this possible with only one flash node.
>> > But just think about the following system configuration:
>> >
>> > One Intel Strataflash (compatible = "cfi-flash") and one non-cfi
>> > compatible flash (e.g. compatible = "jedec-flash"). And the user wants to
>> > define a partition that spans over both flash chips. How could this be
>> > described in one flash node?
>> >
>> >> Do additional properties need to be added to describe the concat layout?
>> >
>> > Not sure. If we have multiple identical devices they can currently be
>> > described in one flash node. So with some changes to the physmap_of
>> > driver this configuration will work with concat as well. But more complex
>> > is a system configuration as described above. Meaning two or more
>> > non-identical chips. I don't see how this could be described in a sane
>> > way in one flash node.
>>
>> Are there any such platforms?
>
> Yes, I know some. Even though they are currently not used with a partition
> spanning over those multiple chips (jedec and cfi).

OK

>> Is there much likelihood that such a
>> platform will be created?  Would it even be a good idea to span
>> partitions across such an arrangement given that different devices
>> will behave differently?
>
> OK, in the example above such a spanning partition is not so likely. But think
> about my original example, the Intel P30 with two different cfi compatible
> chips on one die. Here a partition spanning over both devices is very likely.

I agree.  Same thing when two or more flash chips are put on a board
in consecutive addresses.  I've worked on plenty of these arrangements
myself.

This case really does sound like a driver bug and that the existing
cfi-flash binding is sufficient to describe the hardware.  IIUC, when
all the flash chips are of the same type the physmap_of driver should
be smart enough to detect each of the flash chips within the reg
range.

If I'm wrong and it cannot do this, then it would be a simple matter
of adding an additional tuple to reg for each discrete chip.  A
simple, backwards compatible extension which doesn't require a new
binding.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.