Subject: Re: Flat device tree definitions for FLASH and MTD partitioning

From: Sergei Shtylyov <[email-masked]>
Date: Thu, 26 Apr 2007 16:36:41 +0400

Hello.

Wolfgang Grandegger wrote:

>>>>>>>> are there already some thought or even example code on how to 
>>>>>>>> define Flash memory and MTD partitions in the DTS. This would 
>>>>>>>> avoid the ackward MTD partitioning via static structure or boot 
>>>>>>>> line argument and could be done in a generic way.

>>>>>>>     See Documentation/powerpc/booting-without-of.txt and 
>>>>>>> drivers/mtd/physmap_of.c for what's been already done.

>>>>>>    I meant drivers/mtd/maps/physmap_of.c

>>>>> I had a closer look to this driver. Unfortunately, it can not 
>>>>> handle yet  multiple FLASH banks. This could be achieved with an 
>>>>> additional property "bank_count". What do you think?

>>   Please use hyphen, not underscore in property names ("device_type" 
>> seems an only exception from this rule).
 
> Yes, I know and I also wondered why an "_" is used for the device type.

   Ask the OF spec. developers. :-)
 
>>>>  I'm not sure what banks you're talking about -- note that this 
>>>> driver is equivalen in functionality to the plain 'physmap' driver 
>>>> and there's inherited "bank-width" property that handles flash banking.

>>> Yes, I know. Nevertheless the driver cannot handle flash regions 
>>> composed of more than on FLASH bank because we need to probe every 
>>> bank. Search for "BANK" in drivers/mtd/maps" to understand what I mean.

>>   Hm, from what I could see, those banks are separate maps registered 
>> to MTD subsys separately.
>> What's the point of adding a count property when we simply can define 
>> multiple "rom" devices?
 
> To complete this thread, physmap_of can map _one_ FLASH region composed 
> of one or more FLASH banks. But it currently cannot map more than _one_ 
> FLASH region.

   I wodner why?! :-O

> It would be nice to extend it for multiple FLASH 
> definitions (could code it when time permits).

   I'm seeing nothing that prevents it from working now -- it should register as much "rom" devices as you supply via the device tree.

> Wolfgang.

MBR, Sergei