On Wed, Oct 28, 2015 at 9:40 AM, Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx> wrote: > On 22 October 2015 at 23:27, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote: >> On Thu, 2015-10-22 at 15:04 +0200, Tomeu Vizoso wrote: >>> On 22 October 2015 at 00:51, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote: >>> > On Wed, 2015-10-21 at 08:44 -0500, Rob Herring wrote: >>> > > On Wed, Oct 21, 2015 at 12:54 AM, Scott Wood <scottwood@xxxxxxxxxxxxx> >>> > > wrote: >>> > > > On Mon, 2015-09-21 at 16:03 +0200, Tomeu Vizoso wrote: >>> > > > > 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 <tomeu.vizoso@xxxxxxxxxxxxx> >>> > > > > --- >>> > > > > >>> > > > > 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)? > > If the code in pcibios_init() depends on the PCI bus device having > probed, then I would recommend making that dependency explicit by > calling of_device_probe() on the OF node of the PCI controller when > looking it up. > >>> 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? > > The problem is that a device that defers its probe is currently sent > to the back of the queue, and that's undesired in some use cases in > which there's a device that should be up as soon as possible during > boot (and boot takes a long time). So the goal is to change the order > in which devices with dependencies end up probing. > >> 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. You limited it to OF because people complained that other things >> will break. Things still broke. 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? > > Yes, given the amount of breakage that's a sensible option. But in any > case and even if this series is most likely to be dropped, I recommend > to make explicit as many implicit dependencies as possible. It is dropped for now, but I expect much of this to still integrate with Rafael's proposal. However, it will need to be opt-in it seems. That is somewhat unfortunate because things like async probe are opt-in and seem to rarely get used. As to how we can make it opt-in, I think we can make of_platform_populate() callable multiple times at the root level. This will allow a platform to skip calling it and then a late call to it can register the devices after drivers have registered. This late call will then be a nop for platforms that don't opt-in and call of_platform_populate themselves. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
