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Message-ID: <CAAObsKDR6pTEDK-G+jw+cr9MD-XoZqU8niqvDFHqFM0ve-+Smw@mail.gmail.com> Date: Wed, 28 Oct 2015 15:40:31 +0100 From: Tomeu Vizoso <tomeu.vizoso@...labora.com> To: Scott Wood <scottwood@...escale.com> Cc: Rob Herring <robh+dt@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Stephen Warren <swarren@...dotorg.org>, Javier Martinez Canillas <javier@....samsung.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Mark Brown <broonie@...nel.org>, Thierry Reding <thierry.reding@...il.com>, Alan Stern <stern@...land.harvard.edu>, "Rafael J. Wysocki" <rjw@...ysocki.net>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Dmitry Torokhov <dmitry.torokhov@...il.com>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, Linus Walleij <linus.walleij@...aro.org>, "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>, linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, Hu Mingkai-B21284 <Mingkai.Hu@...escale.com> Subject: Re: [PATCH v6 22/22] of/platform: Defer probes of registered devices On 22 October 2015 at 23:27, Scott Wood <scottwood@...escale.com> wrote: > On Thu, 2015-10-22 at 15:04 +0200, Tomeu Vizoso wrote: >> On 22 October 2015 at 00:51, Scott Wood <scottwood@...escale.com> 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@...escale.com> >> > > 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@...labora.com> >> > > > > --- >> > > > > >> > > > > 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. Regards, Tomeu > -Scott > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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