[PATCH] powerpc: Create "rom" (MTD) device prpmc2800
Sergei Shtylyov
sshtylyov at ru.mvista.com
Sun Jun 3 14:59:27 EDT 2007
Segher Boessenkool wrote:
>>>>> I think "direct-mapped" as compatible is a bit too broad or vague.
>>>> It's actually not -- it means simple 1:1 address mapping (w/o
>>>> explicit
>>>> byte-swapping and such).
>>> Which has nothing to do with "compatible"; instead,
>>> it is implied by the parent node have a "ranges"
>> No! It doesn't have anything to do with "ranges" of parent (don't
>> even know why it would). :-O
> So learn about it please? "ranges" means exactly that:
> child nodes' address space is direct mapped.
Well, now we certainly need a parent node -- which would be static bus
controller? But those have multiple chips selects, so we should know which
range to use. Ugh...
>>> property. Or you can put some other property in
>>> the flash node for all I care, if that seems
>>> necessary for certain cases.
>> Erm... it's *certainly* necessary to mark this somewhere.
> Not if it's redundant information.
>>>> Note that we're matching by both "device_type" and "compatible".
>>> Which is wrong.
>> Why?
> Because that is a) not what you are supposed to do according
> to the standard (so it might very well not work with a
> "third-party" device tree that equally conforms to the standard);
> b) "device_type" describes some other information (namely, the
> OF programming model for the device node) that is completely
> unrelated to the process of driver matching; and c) it is wholly
> redundant to the information in "compatible" *ANYWAY*.
Hm, well. Than changing "compatible" prop would make sense.
>> And why then it's allowed to match by "device_type"?
> Anything is allowed, this is a free world. It is wrong though.
> Linux used to do this wrong, there are many remnants of that
> left. You also might *need* to do this for certain imperfect
> device trees. None of this is an argument to continue this
> "tradition".
>> And why you haven't complained at MPC5200 IDE driver
> Since no one paid me to review the code? Please don't try
Sigh, nobody pays me for that too. :-)
> that argument ever again, thank you very much. I think I
> do quite enough work here already, I don't need people
> demanding stuff from me.
I wasn't demanding anything. I just wanted to clear things out.
>> which does the same (well, maybe you have :-) or at PowerMac IDE
>> driver which matches wither by "name" or "device_type"? Well, quite a
>> lot of drivers are doing this...
> See before why that may be. Short answer is "history".
Well, at least that's cleared.
>>>> This would serve no purpose, as the driver that would catches
>>>> all these is signle one, drivers/mtd/maps/physmap_of.c...
>>> With the current kernel version, perhaps. Did you check
>>> out 2.6.28? Does it work with that?
>
>> For the simply mapped flashes, physmap_of will suffice, for more
>> complex cases, other driver will be needed.
> Ah, so you can predict the future of the Linux kernel!
If I could, I'd have taken measures. :-)
>> If you're hinting at the possibility that MTD subsys will be
>> substantially reworked -- I don't find that likely. If it will --
>> well, bad luck. :-)
> Which is not an acceptable outcome.
>> Anyway, reasonable suggestions on how to make MTD nodes more viable
>> are always welcome. I just haven't seen reasonable enough yet. ;-)
> I suggest you read, and try to understand, some of the base
> device tree specifications first.
Read them some months ago -- do you think I would have plunged into that
not reading anything first? :-/
> Segher
WBR, Sergei
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