Re: [PATCH] e500v2 36 bit large physical HID0[EN_MAS7_UPDATE]

[Scott Wood <scottwood@freescale.com>]

On Wed, Jun 16, 2010 at 09:23:38AM -0500, Timur Tabi wrote:
> I'm sorry, but Linux does depend on the boot loader,

In some ways, but we try not to do so too gratuitously.

> and U-Boot does need to know whether Linux is going to use 36-bit
> addressing.

U-Boot knows whether it puts things over 4GiB.  If Linux is going to change
the LAWs in what was previously a 32-bit physical system, it doesn't seem
unreasonable for it to set EN_MAS7_UPDATE.

> That's just the way it works.  Linux patches that repeat what U-Boot
> already does just so that you don't need to update your U-boot are going
> to be rejected.

Why'd we do cuboot then?  Or any other compatibility measure (e.g. working
with old device trees) or board-specific non-OS-specific init thing which
might be better off done in firmware (e.g. setting up I/O pins to match
what's on the board)?

Firmware is harder to upgrade than a kernel, sometimes it's not worth it.

Especially if new firmware won't boot old OSes, which could be the case with
EN_MAS7_UPDATE on a non-36-bit-aware OS (compatibility is the reason that
bit exists).

-Scott