[PATCH v3 3/4] powerpc: NAND: FSL UPM: document new bindings

Grant Likely grant.likely at secretlab.ca
Thu Mar 26 01:09:33 EDT 2009

On Wed, Mar 25, 2009 at 2:48 PM, Wolfgang Grandegger <wg at grandegger.com> wrote:
> Grant Likely wrote:
>> For the chip offset, it's not clear what the meaning is.  First, does
>> the UPM controller support access of multiple chips simultaneously?
> The offset drives the corresponding address lines, which are used to
> select the chip. That's how it's done on the TQM8548 board. In
> principle, the chips could also be selected through dedicated GPIO pins.
> Well, I'm not a hardware guy.

Heh.  I mean elaborate in the binding documentation.  :-)

>> If so, then can you elaborate in the description on how board design
>> translates to a chip-offset value.  If it cannot, then it might be
>> better to have multiple tuples in the 'reg' property for each discrete
>> chip.  Multiple reg tuples would also remove the need for the
>> num-chips property.
> The node still describes one device mapping all relevant control
> registers. How about using fsl,upm-chip-offsets = <0x200 0x400>. It
> would be more generic and makes num-chips obsolete as well. And the
> property would be reserved for that way of implementing the chip select
> in hardware.

It really sounds like this binding is describing multiple NAND chips
mapped to different base addresses (and looking at the fsm_upm.c
driver appears to confirm it).  So, does this work?  reg = <3 0x200 4
 3 0x400 4>;

It is true that other methods could be used for implementing the chip
select, but that is *not* what the proposed binding describes.  This
proposed binding describes NAND chips selected by address lines
(particular addresses), and in this case I think using reg is the
natural description.


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

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