[PATCH 2/2] [POWERPC] Describe memory-mapped RAM&ROM chips of bindings
laurentp at cse-semaphore.com
Thu Mar 27 05:37:17 EDT 2008
On Wednesday 26 March 2008 15:52, Segher Boessenkool wrote:
> > + Dedicated RAM and ROM chips are often used as storage for
> > temporary or
> > + permanent data in embedded devices. Possible usage include
> > non-volatile
> > + storage in battery-backed SRAM, semi-permanent storage in
> > dedicated SRAM
> > + to preserve data accross reboots and firmware storage in
> > dedicated ROM.
> > +
> > + - compatible : should contain the specific model of RAM/ROM
> > chip(s)
> > + used, if known, followed by either "physmap-ram" or
> > "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'.
> 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
map_ram driver for erase operations (mapram_erase in
drivers/mtd/chips/map_ram.c). To be honest I'm not sure why it uses such an
inefficient approach instead of memsetting the whole area.
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