Re: [bg-linux] [PATCH 6/7] [RFC] enable early TLBs for BG/P
From: Benjamin Herrenschmidt
Date: Fri May 20 2011 - 18:21:07 EST
On Fri, 2011-05-20 at 08:01 -0500, Eric Van Hensbergen wrote:
> On Thu, May 19, 2011 at 10:52 PM, Benjamin Herrenschmidt
> <benh@xxxxxxxxxxxxxxxxxxx> wrote:
> >> Unfortunately, the firmware is also required:
> >> - to configure Blue Gene Interrupt Controller(BIC)
> >> - to configure Torus DMA unit. e.g. fifo
> >> - to configure global interrupt (even we don't use, we need to disable
> >> some channel correctly)
> > Can't we just write bare metal code for that ?
> The kittyhawk code has the bare-metal equivalents for all of these.
> When I get to the drivers, I'll favor the kittyhawk versions for
> submission and then we'll see if it would be possible to adapt the HPC
> extensions to use the bare-metal versions of the drivers versus the
> firmware interface.
Ok. We can also start with using the FW and then migrate to bare metal.
> >> - to access node personality information (node id, DDR size, HZ, etc) or
> >> maybe we can directly access SRAM?
> > That should be turned into device-tree at boot, possibly from a
> > bootloader or from the zImage wrapper.
> This is the approach is used by the kittyhawk u-boot approach.
> However, it would also be just as easy to construct an in-memory
> device-tree within Linux by mapping the personality page and copying
> the relevant bits out. This has the advantage of being able to boot
> Linux directly on the nodes without an intermediary boot loader (which
> kittyhawk uses just to allow us customize which kernel boots on a
> node-to-node basis whereas the stock system boots the same kernel on
> all the nodes within a partition allocation (64-40,000 nodes)).
We can do that from the zImage wrapper... that would be nicer than doing
it from the kernel itself unless there's good reasons to do so like
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