linux-kernel - Re: [PATCH v6 22/22] of/platform: Defer probes of registered devices

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Message-ID: <CAAObsKAfufBe_SycibUN3ZsE3fOkBfUjZRx1SWEMwVtM6t7inQ@mail.gmail.com>
Date:	Thu, 22 Oct 2015 15:04:59 +0200
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 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, I don't see any reason why PPC wouldn't benefit from this
series.

Regards,

Tomeu

>> Any plans to fix this and make PCI hosts hotplugable? For the scanning
>> part, generally the host controller drivers are responsible for
>> scanning their bus now.
>
> Scanning from the host controller driver seems like a reasonable goal, though
>
> it'd take a bit of digging to extract whatever other things fsl_pci may
> depend on from the common PPC PCI code, in particular the various things that
>
> pcibios_resource_survey() does after all PCI buses have been scanned.
>
> There's also check_swiotlb_enabled(), another subsys_initcall, which frees
> the swiotlb memory if ppc_swiotlb_enable hasn't been set.  The PCI host
> controller probe sets ppc_swiotlb_enable if it wasn't able to create an
> inbound mapping for all RAM.  Even if we were to change that to a later
> initcall, there's nothing later than late_initcall that we could use.
>
> -Scott
>
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