Zynq-7020 SoC on-chip-memory

[Ian Lepore]

On Thu, 2015-03-19 at 13:38 -0600, Warner Losh wrote:
> > On Mar 19, 2015, at 1:19 PM, Thomas Skibo <ThomasSkibo at sbcglobal.net> wrote:
> >> Any advice on how to add this memory to my system?
> > 
> > I think it might be more trouble than it’s worth.
> 
> I do too. I tried back in the day to map Atmel’s small cache of RAM into the OS
> as well. It didn’t go well.
> 
> You likely don’t want to use this 256kB for general purpose memory anyway. You’ll
> likely want to use it for something special. For Atmel, I was looking at running interrupt
> handlers and/or ethernet packets through that memory… There were issues with doing
> either one of these that I can no longer recall...
> 
> Warner
> 

My vague plan for a long time has been to try to get L1 page descriptor
tables into this sort of ram.  Often the on-chip ram can be accessed at
the same speed as L1 cache so it would be a big win.

Sometimes when a SoC has on-chip crypto accellerator hardware, this
on-chip ram (or some portion of it) needs to be dedicated to it.

If it's described in the memory region data in FDT it'll just get handed
over to the vm subsystem as available memory, and get allocated for
who-knows-what.

-- Ian