On Wed, May 30, 2018 at 12:44:29AM -0700, okaya at codeaurora.org wrote:

On 2018-05-30 00:37, Christoph Hellwig wrote:

quoted

On Tue, May 29, 2018 at 09:41:33PM -0700, Sinan Kaya wrote:

quoted

Bjorn and I discussed the need for such a "safe" mode feature when you
want to bring up PCI for a platform. You want to turn off everything
as
a starter and just stick to bare minimum.

Can we please make it a config option the instead of adding code
to every kernel?  Also maybe the bringup should be in the name
to make this more clear?

One other requirement was to have a runtime option rather than compile time
option.

When someone reported a problem, we wanted to be able to say "use this
option and see if system boots" without doing any bisects or recompilation.

This would be the first step in troubleshooting a system to see if
fundamental features are working.

I don't mind changing the name
Bjorn mentioned safe option. I made it safemode. I am looking at Bjorn for
suggestions at this moment.

This *was* my idea, but I'm starting to think it was a bad idea.

I don't want people to use pci= parameters as the normal way to get a
system to boot.  That would be a huge support hassle (putting things
in release notes, diagnosing problems when people forget it, etc).

But the parameters *are* useful for debugging.  If we had a
"pci=safemode" and it avoided some problem, the next step would be to
narrow it down by using the more specific flags (pci=nomsi, pci=noari,
pci=no_ext_tags, etc).  So I think 95% of the value is in the specific
flags, and a "pci=safemode" might add a little bit of value but at the
cost of a small but nagging maintenance concern and code clutter.

Bjorn