Re: [PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings

[Laurent Pinchart <laurentp@cse-semaphore.com>]

On Wednesday 26 March 2008 15:52, Segher Boessenkool wrote:
> > +    Dedicated RAM and ROM chips are often used as storage for=20
> > temporary or
> > +    permanent data in embedded devices. Possible usage include=20
> > non-volatile
> > +    storage in battery-backed SRAM, semi-permanent storage in=20
> > dedicated SRAM
> > +    to preserve data accross reboots and firmware storage in=20
> > dedicated ROM.
> > +
> > +     - compatible : should contain the specific model of RAM/ROM=20
> > chip(s)
> > +       used, if known, followed by either "physmap-ram" or=20
> > "physmap-rom"
> > +     - reg : Address range of the RAM/ROM chip
> > +     - bank-width : Width (in bytes) of the RAM/ROM bank. Equal to the
> > +       device width times the number of interleaved chips.
> > +     - device-width : (optional) Width of a single RAM/ROM chip. If
> > +       omitted, assumed to be equal to 'bank-width'.
>=20
> Maybe I'm rehashing some old discussion here, if so, sorry; but why
> do you have bank-width and device-width here?  What useful information
> does it provide?  If this is about saying what the preferred (or only
> possible) access width is, better names are in order.

device-width isn't used so we can get rid of it. bank-width is used by the=
=20
map_ram driver for erase operations (mapram_erase in=20
drivers/mtd/chips/map_ram.c). To be honest I'm not sure why it uses such an=
=20
inefficient approach instead of memsetting the whole area.

=2D-=20
Laurent Pinchart
CSE Semaphore Belgium

Chauss=E9e de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
=46 +32 (2) 387 42 75