On Thursday, October 22, 2015 04:27:10 PM Scott Wood wrote:

On Thu, 2015-10-22 at 15:04 +0200, Tomeu Vizoso wrote:

quoted

On 22 October 2015 at 00:51, Scott Wood [off-list ref] wrote:

quoted

On Wed, 2015-10-21 at 08:44 -0500, Rob Herring wrote:

quoted

On Wed, Oct 21, 2015 at 12:54 AM, Scott Wood [off-list ref]
wrote:

quoted

On Mon, 2015-09-21 at 16:03 +0200, Tomeu Vizoso wrote:

quoted

Instead of trying to match and probe platform and AMBA devices right
after each is registered, delay their probes until 
device_initcall_sync.

This means that devices will start probing once all built-in drivers
have registered, and after all platform and AMBA devices from the DT
have been registered already.

This allows us to prevent deferred probes by probing dependencies on
demand.

Signed-off-by: Tomeu Vizoso <redacted>
---

Changes in v4:
- Also defer probes of AMBA devices registered from the DT as they 
can
  also request resources.

 drivers/of/platform.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

This breaks arch/powerpc/sysdev/fsl_pci.c.  The PCI bus is an OF 
platform
device, and it must be probed before pcibios_init() which is a
subsys_initcall(), or else the PCI bus never gets scanned.

Thanks for the report. This is probably getting dropped, but it could
be disabled for PPC.

I don't think that adding another arbitrary arch difference would be the
right solution.

I think Rob meant temporarily disable it while things get fixed. At
least, 

So, what is the permanent fix for the swiotlb issue (or more generally, the 
inability to have a late_initcall that runs after non-module, non-hotplug 
platform devices have been probed)?

quoted

I don't see any reason why PPC wouldn't benefit from this
series.

It's not clear to me what the benefit of this is at all, much less for PPC.   
What is the fundamental problem with deferred probes?  In the cover letter 
you say this change saves 2.3 seconds, but where is that time being consumed? 
 Are the drivers taking too long in their probe function trying to initialize 
and then deferring, rather than checking for dependencies up front?  Or are 
there really so many devices and such a pessimal ordering that most of the 
time is spent iterating through and reordering the list, with each defer 
happening quickly?

Even if something different does need to be done at this level, forcing all 
OF platform devices to be probed at the late_initcall level seems quite 
intrusive.

Totally agreed.

You limited it to OF because people complained that other things 
will break.

Right.

And I'm not sure why that was regarded as a good enough reason to do it.

Things still broke.

Yes, they did.

Surely there's a better way to address the 
problem.  Can't the delay be requested by drivers that might otherwise need 
to defer (which could be done incrementally, focusing on the worst 
performance problems), rather than enabling it for everything?

Well, I was suggesting to use an opt-in flag there, but I'm not sure if Tomeu
took that into consideration.

In any case, probing is just one aspect of a deeper issue, which is that
we have no way to represent functional dependencies between devices.

Thanks,
Rafael