[PATCH 1/9] ARM: vexpress: remove automatic errata workaround selection

On Wed, Jul 11, 2012 at 04:02:05PM +0100, Rob Herring wrote:

On 07/11/2012 08:36 AM, Pawel Moll wrote:

quoted

From: Will Deacon <redacted>

The vexpress Kconfig setup tries to be clever^Whelpful and selects some
errata workarounds for certain revisions of the Cortex-A9 and PL310,
which may be required depending on the coretile.

Since the mach-vexpress can support A5, A7 and A15 coretiles, let's
defer errata workaround selection to the user and instead propose
recommended workarounds in the defconfig. Note that the use of the
savedefconfig target removed some unrelated, redundant entries from the
file.

Most workarounds are runtime conditioned or don't have significant
impact, so why not leave them enabled? For a single kernel image, we're
going to have to basically turn on every errata work-around. Perhaps we
should only have config options if they are not runtime enabled and have
significant performance impact. I think having the settings in the
defconfig is error prone, not mention if threats from Linus to remove
all defconfigs actually happened it would be lost. In general, I don't
think end users have enough information to determine what needs to be
turned on. You need the errata list as well which is not public. Some of
the errata help text says "rXpY and all later revisions" which changes
when a new core revision comes out.

The problem I have with the current scheme for vexpress is that you can't
disable the workarounds when you know they are not needed. The Kconfig
*forces* them to be enabled -- that's certainly not right. Of the
workarounds in question, ARM_ERRATA_720789 is not runtime enabled and I
would like to deselect if when running on my A5, A7 or A15 cores. The
description clearly states it's an A9 erratum, so I don't think users will
have any difficulty knowing that they don't need it for other cores
(although I agree that it should be enabled for single zimage).

The defconfig changes were just a courtesy to reflect the change in the
Kconfig, I'm happy for them to be dropped.

Will